Mechanized Memory and Logic — What Electronics Can Do, J. H. Felker 201
Use of Transistor in New Military Telephone System, H.C. Fleming 4 207 :
The Speakerphone, W. Clemency 208
Ultrasonic Delay Lines, J. b. May, Jr. 212
Improved Key Handle for PBX Switchboards, H. J. Smith 217 :
Arcing at Telephone Relay Contacts, I’. Kisliuk 218
Repeaters Military Telephone, Jr. 227
4 The 1956 A. & Stockholders Meeting

at Murray Hill Laboratory 234
THE COVER: Mrs, R. A. MacAllister of the Outside Plant EDITORIAL BOARD
Development Department conducts sea water bleaching tests
on jute protective covering used in submarine cable. F. J. Singer, Chairman
A. Hornbeck
F. A. Korn
E, T. Mottram
The BELL LABORATORIES RECORD is published monthly by Bell Telephone R. J. Nossaman
Laboratories, Incorporated, 463 West Street, New York 14, N. Y., M. J. KELLY, W. E. Reichle
President; M. B. LONG, Seeretcry and Treasurer. Subscriptions: $2.00 per A. H. White
year; Foreign, $2.60 per year, Checks should be made payable to Bell Labora-
tories Record and addressed to the Circulation Manager. Printed in U. 8. A. EDITORIAL STAFF
© Bell Telephone Laboratories, Incorporated, 1956. A D. Tebo, Editor

G. E. Schindler, Jr., Assistant Editor, Murray Hill
R. C, Sanford, Assistant Editor

who are familiar only with present-day telephone equipment. Despite its
seeming complexity, however, electronic switching promises a wholesale sim-
plification of telephony. Laboratories engineers believe that in the future
it will be a faster and more economical way to provide telephone service.

In many magazines and newspapers you may see
claims about the “magic” of electronics. As tele-
phere people, we are not interested in magic, but
we are interested in the capabilities of electronics,
because electronics will penetrate into areas of the
telephone business that either have never been
mechanized before or have been mechanized by
other means. Perhaps we can sharpen our apprecia-
tion of the part electronics can play by first examin-
ing the characteristics that cause people to associate
words like “magic” with it.

Looking for fundamentals, we may inquire,
“What puts the magic into modern electronics?”
The answer comes in two parts: (1) the ability to
develop tremendous but stable amplification, and
(2) the ability to perform complex operations in
millionths of a second. The first of these is familiar
to telephone people, for it is the basis of our mod-
ern telephone transmission plant. Electronic ampli-

fiers are the muscles of our transmission system.
The second is being applied extensively in new
switching systems now under development.

The automatic tracking radars developed at Bell
Laboratories and manufactured by Western Elec-
tric are a splendid example of these two abilities
of electronics. The Nike guided missile system,
Figure 1, naturally excites a writer to the use of
words like “magic” and “giant brain” when he
attempts to describe its performance, Without the
magic of almost unlimited amplification, the radar
would never be able to hear the radio echo which
bounces off an airplane many miles away and
spreads out into space, because only an extremely
small fraction of the energy returns to the radar
antenna. This small echo is amplified billions and
billions of times and is strengthened to where it
can drive motors which cause the radar antenna to
follow the enemy plane as it goes across the sky.

At the proper instant a missile is launched by the
Nike system, and here the system shows its brain
power. By exploiting the ability of electronics to
perform complex operations in microseconds, an
electronic computer guides the missile toward the
target. Even if the target should attempt to evade
the missile, the very high speed computer takes

account of the evasion, and the missile proceeds
inexorably to the interception.

Since the telephone plant is not a radar system
and since telephone customers do not need to be
connected together in microseconds, how shall the
second magic-giving characteristic of electronics
be exploited in the telephone plant? The answer is,
“Through time sharing”. Now, time sharing is just
another way of describing the common-control
operations that we introduced into the telephone
plant with the dial system many years ago, With
common control, one expensive piece of equipment
performs in sequence the same function for a num-
ber of different customers. We are limited in time-
sharing electromechanical devices because of their
limited speed. When we go to electronics, however,
we can design complex equipment which completes
a function in a few millionths of a second and is
then ready to do something else. To appreciate the
full power of such electronic speeds, consider a
machine that can complete an operation every
millionth of a second. Assume also that a man may
take a minute to perform the same operation, At

these speeds the machine could perform as many
operations in a minute as a man could by working
night and day for an entire lifetime. Such speed
results in great economic advantages for electronics.

We can develop some insight into the fundamen-
tals of time sharing by analyzing the case of the
chessmaster, who sometimes plays and wins as
many as 30 games of chess simultaneously. Now he
doesn't really make the individual moves of these
games simultaneously. He moves quickly from
board to board and takes on each opponent in turn.
He has memorized the positions of the pieces and
the previous history of each game, and all he has
to do is detect the new move made by an opponent.
He rapidly decides upon his next move, executes
the move, and then goes to the next board. Note
what this chessmaster has been doing, First of all,
the whole secret of his success is his ability to
remember a tremendous amount of information. In
fact, he carries around with him a memory of all
the games. The other ingredient in his success is
the ability to make decisions very rapidly. As a
result, his 30 opponents are, in effect, engaged con-
tinuously. We can do this kind of time sharing in
telephony with modern electronics.

Imagine now a central office which has a built-in
“chessmaster”, This electronic wizard plays a game
with each telephone customer who wants service.
His goal is to meet the service needs of each cus-
tomer, The “boards” the “telephone-master” uses
are the lines of 10,000 or so telephones that come
into the office. The “telephone-master” continu-
ously scans these lines to determine if service is
requested, He remembers what progress he has
made in carrying out the wishes of each of the
customers, and he makes decisions on what his next
move with each customer should be. He does all
these things so rapidly that every telephone user
thinks he has the undivided attention of the central
office equipment.

The chessmaster used both memory and logic,
and it is primarily because memory and logic have
been mechanized in modern electronic computers
that people compare these machines to the human
brain, Since mechanized memory and logic will
be at the center of future telephone switching
systems, it is important to understand their funda-
mentals and applications.

We may call to mind one example of mechanized
memory from the folklore of the wild West. Every
time a gun-fighter killed a man he cut a notch on
the stock of his gun, Any time he wanted to refresh
his memory he could go to the “mechanized mem-

ory” on the gun stock and run his finger down it.
This may seem like a rather trivial example, but it
illustrates some of the fundamental principles of
mechanized memory systems. A modern counter-
part of the notched gun stock is the punched card
used in modern accounting machines. This card
has holes punched in it, and the positions of these
holes represent information. A punched card can,
for example, remember a man’s social security num-
ber or it can remember his rate of pay.

To understand the ideas behind electronic mem-
ory it is well to keep in mind the idea of a notch, or
a hole, or some other physical modification as the
basis for mechanized memory. Other key ideas will
be explained with reference to Table | in which
are listed some of the words and phrases used in de-
scribing electronic memory systems.

A very basic word is Brr—a_ contraction of
BINARY bicrr. A Bir is the elementary unit of infor-
mation. It is the yes or no answer to a question, The
power of such answers is indicated by the familiar
game of 20 questions. As you know, by asking no

more than 20 questions it is generally possible to
find out which object out of all the objects in the
world a person has in mind. The following example
shows how yes-no answers can be used to repre-
sent numbers. Suppose someone has a number
between zero and 31 in mind and we ask this person
in succession the following questions and get the
answers indicated.

“Is the number greater than 15?” “Yes.” “Is the
number greater than 23?” “Yes.” “Is the number
greater than 27?” “No.” “Is the number greater than
25?” “No.” “Is the number greater than 24?” “Yes,”
Now from this pattern of answers — Yes, Yes, No,
No. Yes — we know that the decimal number is 25.
We can write the number twenty-five in binary no-
tation by saying that “yes” corresponds to the digit
one and a “no” corresponds to the digit zero. Thus
the binary number twenty-five is written 11001. By
asking five questions we have determined the magni-
tude of a number between zero and thirty-one. By
asking ten questions we could have identified any

number between zero and a thousand. By asking
20 questions we could have identified any number
between zero and a million. Thus any number be-
tween zero and a million could be written as a 20-
digit binary number.

Why bother with binary representation of num-
bers? The reason is that a binary digit is something
like a notch on a gun or a hole in a paper card. It
is very definite. There is either a hole in a card or
there isn't. Similarly a binary digit is either a one
or it isn’t. Binary digits can be convenie ntly repre-
sented by a variety of components. For example,
a relay is either operated or not operated, We can
say that the operate condition represents a one
and the unoperated condition represents a zero.
Similarly, a transistor can be allowed to represent
a one when it conducts or a zero when it is not con-
ducting. A capacitor can represent a one when it
contains stored electrical energy, whereas an un-
charged capacitor can be used to represent a zero.
A magnet can be magnetized in such a way that the
north pole is at the top or it can be magnetized
so that the north pole is at the bottom. Thus the
number twenty-five might be represented as a row
of magnets that are magnetized North-North-South-
South-North.

In addition to the problem of providing the indi-
vidual memory cells, the designer of a mechanized
memory system must provide many other features
indicated by some of the words in Table 1, These
functions will be explained with reference to Figure
2, which shows a pigeonhole memory system. As-
sume each pigeonhole has a card in it, Figure 2 (a),
and that information or remembered
on each card. Going to the memory and selecting a
particular card is the access operation. The neap
operation is simply the operation of looking at the
card, Clearly, the access operation must precede
the reap operation. Similarly, to wrrre into the
memory involves an access operation, because we

A “pigeonhole
in holes and access to address D3;
holes and binary digits 11001 registered in Row 4,

must first find the card we are interested in. To
gain access to information systematically, it is cus-
tomary to provide addresses which give instructions
on how to get to each pigeonhole. appress ps, for
example, says go out to the p column and then pro-

ceed down to the third row to information cell ps.
With the aid of such a pigeonhole memory system,
we have developed the fundamental ideas of mech-
anizvd memory — the idea of appress, the problem
of access, the concept of Binary picrrs and BIT OF
INFORMATION, the warre operation and, finally, the
READ operation.

An electronic system, however, could not be
based on a man running around writing on cards,
so a more suitable record is needed to put in
the pigeonholes. Earlier, when developing the ide:
of bits of information, it was pointed out that a
capacitor could be used to store information, To
develop a memory system, we can obtain lots of
‘apacitors and put one in each pigeonhole, Figure
2(b). Suppose you want to write the binary num-
ber 11001 into the memory. First of all, at what
address will the information be written? Assume
that it is to be written in Row 4, Proceed down to
Row 4. The first digit is a one, so charge the first
capacitor, Since the second digit is also a one,
charge the second capacrror. Since the third and
fourth digits are zeros, leave the third and fourth
capacirors uncharged, The fifth digit is one, so
charge the fifth caracrrorn, Other numbers might
be stored in other rows. To read the number at
Address 4 at a later time we would short circuit the
capacrrors in Row 4; whenever we got a spark we
would know that a one had been stored.

This leads to another basic idea. After the infor-
mation has been read, where has the information
gone? It has been destroyed because short circuiting
‘apacitors Was DESTRUCTIVE READING process.
Memory designers must design REGENERATION into
memory systems in which reading is destructive.
If you want to read information from the capacitor-
memory and still leave the information ready to be
read again at a later time, you must put energy
back into the capacitor if it was storing a one. This

An electronic system with capacitors in the
pigeonholes is not complete because someone has
to walk around charging and discharging the
capacitors, To see how the access problem can be
solved with electronics, consider the ordinary tele-
vision set. As you know, the picture is drawn by a
spot of light that chases back and forth across the
face of the picture tube. This spot of light is a kind
of electronic pencil that is time-shared to draw the
TV picture. Imagine the face of the picture tube
divided into pigeonholes as in Figure 3. The spot
of light on the picture tube can be deflected by
voltages to any desired address in a millionth of a
second, This rapid deflection of an electron beam
provides almost instantaneous access to any one of
a group of pigeonholes.

How can information be stored on the screen of
a cathode ray tube? Physicists have developed a
new kind of tube called a BARRIER-GRID MEMORY
ruBe. This tube is like a TV picture tube except
that it has literally thousands of tiny capacitors
deposited on the screen. The electron beam in this
tube can charge or discharge capacitors. Thus, in
the memory tube, Figure 4, we have a means of
gaining access not to just 25 but to over 16,000

Fig. 4 W. W. Baldwin welding leads to contacts
on glass envelope of barrier-grid memory tube.

pigeonholes. The memory tube then has a memory
capacity of 16,000 bits. To get an equivalent mem-
ory capacity with relays would require 16,000
relays. A memory tube is a splendid example of
the compactness that can be achieved through
electronics. It has, in addition, the tremendous ad-
vantage that reading and writing into the tube
requires only a few millionths of a second.

Fig. 5 — Magnetic-core memory: direction of magnetism
of selected cores is reversed by currents in wires.

magnetic memory. This is another important method
of storing large amounts of information in a small
space. It would be cumbersome if conventional
magnets were used, but physicists have discovered
ways of making up a ceramic-like magnetic material
(ferrite) into little doughnuts called “cores”. In a
magnetic-core memory, Figure 5, electrical con-
ductors run through the holes of numbers of these
doughnuts mounted in an array. Currents passing
through certain of the wires will magnetize or de-
magnetize selected cores.

The chief advantages of magnetic-core memories
are that the ferrite cores can be mass produced
very cheaply, and that we can easily gain access to
the stored information through transistorized cir-
cuits. At present, there is a competition between
magnetic-core memories and memory tubes. Many
of our telephone engineers believe that the me mory
tube is a little faster and a little cheaper than the
core memory, but they recognize that as further
improvements are made in the art the situation may
be likely to change.

Having seen how electronic memory systems will
store thousands and even millions of bits of in-
formation, it is appropriate to consider mechanized
logic. We have had logie circuits in the telephone
plant for years — they are the circuits that deduce
the logical results of the inputs to the circuits. As
an example of logic, consider the plight of a fellow
named Joe who belongs to a riding group. Every
third day it’s Joe’s turn to drive to work. But things
don't often work out that way because somebody
is always having to take someone else's turn for one
reason or another. Suppose that Joe comes home
from work some evening and his wife says: “Honey,
did you ask the fellows if one of them could drive
for you tomorrow?”

Joe says, “Sure I asked them. When I asked Pete
if he’d take my turn, he was just leaving for Phila-
delphia but he said he'd be glad to drive tomorrow
if he didn't have to stay over in Philadelphia and
his wife didn’t need their car. Anyway, Oscar will
probably be able to drive, because his wife has
been staying home lately and he will drive her
car, if she doesn't go to work. He also said that
since his own car is due back from the garage
tomorrow, he can drive it even if his wife does
use hers provided the garage gets the car back to
him. But if this cold of mine gets any worse Um
going to stay home even if those guys have to walk
to work and you'd certainly have the car if 1 am
going to be home.”

To simplify all this, Joe might draw a logical
block diagram like Figure 6 for his wife. The block
diagram has an output, a signal present, whenever
Joe will drive, It has signal inputs on the left. We
have a signal present on the first lead, for ex-
ample, if Peter's wife needs their car. The “or”
circuit is called an “or” circuit because it will have
an output whenever there is a signal on the top on
bottom lead, The “and” circuit will have an output
if there is a signal on its top ANp its bottom lead.
The third type of circuit, called an iNeuerror cir-
cuit, will have an output if there is a signal on the
top lead, unless there is a signal on the bottom lead.
Note that if Joe’s cold is worse, the inuiBrron
functions and regardless of the signal on the top
lead there will be no output because Joe just isn't
going to drive if his cold is worse.

Joe could mechanize the circuit with either relays
or transistors. With the use of transistors, the
circuit could determine its output in a millionth
of a second, In our telephone plant of the future,
there will be an extensive use of transistors for the
kind of logic functions that have in the past been

performed with relays. Since the transistor can be
made to operate in a millionth of a second, we can
time-share these circuits and, like the chessmaster,
reach very fast decisions.

So far we have explored the characteristics that
put the magic in electronics. You have seen how
we can mechanize functions which lead people to
refer to electronic machines as electronic brains.
By analogy with the chessmaster you saw how we
might, through time sharing, build a new type of
electronic switching plant. It is appropriate now to
be more specific about the use of mechanized mem-
ory and logic in building this plant.

In new electronic switching systems which Bell
Telephone Laboratories engineers are now plan-
ning, mechanized memory and logic circuits are
time-shared to control a high-speed switching net-
work, Extensive memory will be used in such
switching systems. Information is stored in both
temporary and permanent memories. The kind of
information which might be stored in the tem-
porary memory can be determined by going back
to the chessmaster or telephone-master analogy.
The telephone-master would store in the memory
tube certain information regarding the lines coming
into the office. Suppose the office is a 10,000 line
office. The machine would look at each line and
observe whether or not the receiver was off the
hook and would then store in the memory a binary
digit which answers the question, “Does the line
corresponding to this memory cell want service or
doesn't it?” The machine would also store for each
line the answer to the question, “Is the line getting
service?” If the answer is “yes” the machine would
not worry about the line. If the answer is “no” the
machine would then prepare to give the line service.
If dial pulses are coming in over the line the
machine will store in its memory the number of
dial pulses received, Note that relay registers might

J. H. Feixer attended Washington University in St, Louis, Missouri, and
received the B.S. degree in Electrical Engineering in 1941. Mr. Felker served
in the U, S. Army from 1942 to 1945, first as a radar maintenance officer and
later as an Army publications officer. He joined the Laboratories in 1945,
where, in the Military Systems Engineering Department, he was in charge of
the development of the Tradic transistor digital computer. In 1955, Mr. Felker
was appointed Director of the Special Systems Engineering II Department,
where he is responsible for long range planning in data processing and trans-
mission. He is a member of the Institute of Radio Engineers, and is past Chair-
man of that organization's Professional Group on Electronic Computers.

have been provided to store the dial pulses. Instead,
the memory is provided wholesale in a big economi-
cal memory system where the dial pulse information
is stored along with the other information.
Because of these new system concepts and new
apparatus such as the transistor and electronic
memories, we can expect to see electronics as the
basis of telephone switching as well as transmission.
Because all functions are achieved by sequences of
logic and memory operations, we expect our equip-
ment to become more flexible. In the future the
same equipment used to set up telephone calls may

AND | INHIBITOR 2)
L OUTPUT:
OSCAR'S CAR IS NOT | WHEN SIGNAL
BACK FROM GARAGE | AND IS PRESENT

“JOE'S COLD 1S WORSE
Fig. 6 — Block diagram illustrating logic behind
answer to question, “Will Joe drive?”

also be used to perform billing and accounting func-
tions, to prepare service orders, and to do circuit
layout engineering. At some stage in the future, we
may have a telephone plant in which the boundaries
between separate functions are not very distinct
because the same machinery is carrying out all of
our operations. Many engineers are confident that
this is the way to simplify and to make cheaper
the cost of doing the telephone job.

A point-contact transistor plays a unique role in
the new military telephone system recently designed
for the Signal Corps.* With this system, twelve
speech channels are transmitted simultaneously over
four conductors twisted into what is termed “spiral-
four” cable. To amplify the signals along the cable
run, electronic repeaters are spaced at intervals of
about 5% miles; many of these repeaters do not re-
quire attendance by operating personnel.

At these unattended repeaters, however, installa-
tion and maintenance tests are sometimes required,
which means that occasionally someone must visit
the site of the repeater and talk to attendants at
other points along the system. A portable test set in
combination with a field telephone is used for this
purpose, The test set includes a transistor which is
used in an oscillator circuit that permits the line-
man performing the tests to signal attended re-
peaters or terminals along the line.

To establish a talking circuit to these points, the
lineman connects the portable field telephone to the
test set. This telephone includes a hand generator
which, when rotated, produces an alternating vol-

tage of low frequency (about 20 cycles per second ).
Such a signal normally suffices for signaling over
the field wire used for other types of military tele-
phone connections. However, the circuit arrange-
ments of the new system do not permit the trans-
mission of these low frequencies, and the receiving-
signaling circuits will not respond to them.

The test set is therefore provided with circuits
(Figure 1) that rectify the 20 cps signal and apply
the resulting de potential to a point-contact tran-
sistor, arranged to oscillate at 1,600 cps. This tone is
transmitted by the cable and is of the correct fre-
quency to cause a response by the receiving-signal-
ing circuits at the attended points. The reception of
the signal is indicated by a lamp and buzzer.

The special characteristics of transistors are used
to great advantage in this circuit. In contrast with
a circuit using electron tubes, the oscillator requires
no warm-up time. Rotating the hand generator
crank less than two turns is sufficient to produce
lamp and buzzer indications at the attended points.
Also, since the small amount of power necessary to
initiate the signal is easily obtained from the hand
generator, no battery power is required, Further,
because of the size advantage of transistors, the
signaling circuit adds little to the volume and weight
of the complete test set. Without the transistor,
signaling could have been accomplished only with
much bulkier and more complex circuits.

TELEPHONE TRANSISTOR
SET
RECTIFIER
“ai | 20% ANO
—_ LIMITER
CIRCUITS --
1600,
HAND TO SPIRAL-
GENERATOR FOUR CABLE

Fig. 1 — Porta-
ble telephone
and test set sig-
naling arrange-
ment, Transistor
circuit’ supplies
1,600 cps tone to
cable,

As the telephone has become a more and more valuable part of normal
American life, the need for many new services has increased. Part of the
Laboratories’ responsibility, acting on the advice of the A.T.&T. Co., is to
anticipate these needs and design the instruments and systems to fulfill them.
One good example of this work is the Speakerphone designed to provide
“hands-free” telephone service under most conditions,

Ever since the invention of the telephone, the
trend of design has been to increase the ease with
which a customer can carry on his telephone con-
versation, Following this trend a new telephone
set, the Speakerphone, that provides hands-free
telephony has recently been introduced for Bell
System use, The customer, using the Speakerphone,
talks into a transmitter about eighteen inches from
his mouth, and listens to a loudspeaker about the
same distance away. The customer can now readily
write notes or refer to charts, reference books, and
correspondence during a telephone call. He con-
verses with the distant caller as if the latter were
seated across the desk from him; this gives the user
considerable freedom of movement. The Speaker-
phone also provides for group participation. During
a call, a number of people seated closely around
a desk can talk freely —the transmitter picks up
the conversation and the replies are heard from the
loudspeaker. This hands-free set is also of consid-
erable value to the physically handicapped.

The location of the acoustic instruments at a
greater distance away from the user as required
for a hands-free telephone set makes the perform-
ance of the Speakerphone more dependent on
room acoustics and room noise than that of a
handset telephone, The handset is used at such
close distances, about one inch for the transmitter
and directly on the ear for the receiver, that the
ordinary environmental acoustic conditions have
little influence. As the distance between the user
and the telephone instruments is increased, how-

ever, room reverberation ansl room noise become
important. Hence the quieter and less reverberant
the room, the better the Speakerphone performance.

A typical desk arrangement for the components
of the Speakerphone is shown in the headpiece of
this article. The housing, similar in appearance to
the 500-type telephone set, contains the transmitter,
on and orF buttons, and the loudspeaker volume
control, in addition to the handset and other usual
components of the 500-type set. The loudspeaker
is located in the small plastic housing shown in the
upper center of the headpiece. The circuit of the
Speakerphone permits independent use of either
the handset or the Speakerphone.

The Speakerphone is easy to use. To place a
call, it is only necessary to momentarily press the
on button which lights up when the set is con-
nected to the line. Then, when dial tone is heard
from the loudspeaker, the number is dialed in the
normal manner. When answering a call, the on
button is momentarily pressed, again causing it to
light up, and the conversation can start. The
transmitter picks up the voice of the user, and the
other person is heard on the loudspeaker. The
volume of the incoming speech is adjusted by
turning the small knob of the volume control. At
the end of the call, the orr button is pressed, dis-
connecting the set from the line.

If privacy is desired during a call with the Speak-
erphone, or if some transmission difficulty is encoun-
tered, lifting the handset automatically transfers
the call to the handset, and turns off the Speaker-

phone. If the handset is being used, and it is
desired to transfer to the Speakerphone, the on
button is depressed while the handset is being
returned to the cradle. The Speakerphone is de-
signed for a talking distance of ten to thirty inches.
The loudspeaker is placed about three feet from
the transmitter and so located that the normal
seated position of the user is midway between the
two instruments.

In addition to the two desk instruments shown
in the headpiece, an apparatus box containing
amplifiers, power supply, and associated circuitry
is part of the Speakerphone. The interior of this
apparatus box is shown in Figure 1. This box is
mounted following usual Bell System practices.

Two amplifiers, each having approximately 50-db
maximum gain, are required, one for the transmitter
and one for the loudspeaker. These two amplifiers
are assembled on a_ printed circuit card which
plugs into a socket in the apparatus box as shown
in Figure 1. When these amplifiers require servicing,
the printed circuit amplifier card can be quickly
replaced. The power supply of the Speakerphone
is energized from a 115-volt, 60-cps power outlet
and consumes 8 watts when the Speakerphone is
in use and 0.6 watt when it is in standby condi-
tion. The handset of the Speakerphone operates
independently of the power supply and will per-
form in its normal manner in case of power line
failure. The other components in the apparatus box
are a relay, a hybrid coil, and input and output
transformers. The instruments shown in the head-
piece and the apparatus box shown in Figure 1,
which together constitute the Speakerphone, are
coded as the 595-type telephone set.

The basic circuit of the Speakerphone is shown
in Figure 2. The hybrid coil, which is a form of
Wheatstone bridge, couples the two-way telephone
line to the output of the one-way transmitting
amplifier and to the input of the one-way receiving
amplifier, and introduces a loss between them (the
output of the transmiting amplifier and the input of
the receiving amplifier). As indicated in Figure 2,
the unavoidable acoustical coupling through the
air path between the loudspeaker and the trans-
mitter forms a closed loop with the rest of the
circuit, This closed loop, when there is power gain
in it, acts as an oscillator causing the loudspeaker
to produce a sustained tone called “singing”. Be-
cause of this, there is an upper limit on the total
permissible gain which can be used in the trans-
mitting and receiving amplifiers.

impedance and the balancing network impedance
determines the loss introduced by the hybrid coil
between the output of the transmitting amplifier
and the input of the receiving amplifier. If a perfect
balance could be obtained at all frequencies, this
loss would be infinite, and singing could not occur.
The impedance of telephone lines varies consider-
ably, however. It may be resistive, capacitive, or
inductive depending on the length of loop to the
central office, the length and type of trunk between
central offices, and in the case of short connections,

also somewhat on the length of loop to the distant
party. This is especially true for a line on a PBX
which, on internal calls, may have a short loop, but
on calls to an external telephone may have a long
loop to a central office. There is, fortunately, a
rough correlation between loop impedance and
loop direct current. The balancing network is de-
signed to be adjusted by this loop direct current,
which produces a voltage across the terminals of
the network. A varistor in the network varies its
resistance in response to this voltage and regulates
the impedance of the network. The network is
designed to produce a better balance on long loop
connections where more loudspeaker gain is re-
quired and singing becomes a limiting factor. Be-
cause both the transmitting and receiving amplifiers
are in the singing loop, it is important that the
gains in these amplifiers be properly apportioned.
The gain of the transmitting amplifier is adjusted
at the factory so that the Speakerphone transmitting
level at a talking distance of eighteen inches is

somewhat below the transmitting level of the 500
set with its transmitter at about one inch from the
user's lips. The loudspeaker volume control, ad-
justable by the user, regulates the gain in the
loudspeaker amplifier circuit. With the fixed gain
in the transmitting circuit, the permissible gain in
the loudspeaker amplifier before singing occurs

is determined by the balance of the hybrid coil
circuit, and the acoustical coupling between the
transmitter and the loudspeaker. As shown in Fig-
ure 3, an increase in distance between the trans-
mitter and the loudspeaker allows more gain to be
used in the loudspeaker circuit. However, beyond a
certain separation, further increase in the distance
between the instruments moves the loudspeaker
further from the listener and hence causes a de-
crease in the signal at his ears for the same loud-
speaker circuit gain. The optimum practical ar-
rangement is to have the user seated approximately
midway between the instruments which are sepa-
rated by about three feet on the desk top.

Figure 3 also indicates that the acoustical prop-
erties of the room influence the acoustical coupling
between the transmitter and the loudspeaker, In
reverberant rooms having very little sound absorp-
tion, the permissible gain in the loudspeaker cir-
cuit before singing occurs is less than that in a room
with sound absorption resulting from acoustical
treatment on the ceiling, carpet on the floors, and
perhaps window drapes. The acoustical properties
of the room also influence the transmitting quality
of the Speakerphone.

Because the transmitter of the Speakerphone is
eighteen inches from the lips instead of one inch
as with the handset transmitter, the ratio of direct
speech to reverberant speech, caused by reflections
from the walls and other solid surfaces in the room,

is less with the Speakerphone than with the handset.
In a room having little sound absorption, these room
echoes are a disturbing influence to the listener at
the other end of the line. In direct person-to-person
conversation, the binaural effect resulting from our
having two ears reduces the effect of such room
echoes. In rooms having good sound absorption, the
echoes are reduced and Speakerphone transmission
is relatively free of this reverberant quality. Further-
more, if the loudspeaker received signal is high,
it is picked up by the transmitter and returned to
the distant talker as a delayed sidetone of his
speech. This effect, caused by the transmitter-to-
loudspeaker acoustical coupling, is small in rooms
having good acoustical properties. To minimize
this delayed sidetone at the called customer's tele-
phone, the loudspeaker volume should not be
greater than is required for comfortable listening.

A thermistor is used in the loudspeaker ampli-
fier to limit the volume of the sound from the loud-
speaker, and to limit the voltage applied to the tele-
phone line if the Speakerphone should sing because
the volume control is advanced too high. The ther-
mistor, designed especially for this application, is
used as a variable resistance shunt across the loud-
speaker transformer as shown in Figure 2. As the
alternating voltage developed by the amplifier in-
creases, the thermistor decreases in resistance and

Fig. 3— Permitted loudspeaker gain versus sep-
aration between loudspeaker and transmitter,

acts to limit the voltage. This action reduces the
singing tone from a disturbing how] to a soft audible
tone, and also limits the voltage applied to the line
to that of the transmitted speech level. In addition,
by acting as a volume limiter on received loud-
speaker signals, the thermistor reduces the magni-
tude of the delayed sidetone at the distant telephone.

The transmitting and receiving frequency char-
acteristics of the Speakerphone are illustrated in
Figure 4. By experiment these response curves have
been found to be good compromises for speech
quality, for the reduction of the effects of room
echoes, and for the control of the singing char-

acteristics of the set. The decrease of receiving
response at the higher frequencies produces a more
pleasant quality for speech received from a con-
nected handset telephone over short lines without
producing a serious degradation of articulation on
long lines. This is due to the fact that the higher
frequencies are augmented by the reflection of
sound waves at the listener’s head so that the re-
sponse in terms of ear canal sound pressure actually
rises at frequencies between 1,500 and 3,000 cycles
per second. These reflections do not occur with the
regular telephone receiver held close to the ear. -
Ambient room noise influences the performance of
the Speakerphone to a greater extent than it does
the performance of the handset. This results from
the greater talking distance of the Speakerphone
transmitter, and the fact that the loudspeaker is

-“ONE MICROBAR SOUND
PRESSURE IN FREE FIELD J
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TRANSMITTER <a-25
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frequency characteris set | Vinw | ARTIFICIAL
tics; top, transmitting, 4 —
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Measurement details are MAXIMUM VOLUME as
CONTROL POSITION 58
given at the left.
22
SOUND PRESSURE _ om
MEASURED AT
THIS POSITION
Se, $e -15
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18” LOUDSPEAKER -20
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heard through an open air path. With a handset,
the receiver cap, when pressed against the ear,
attenuates the ambient noise considerably. With
the Speakerphone, the ambient room noise enters
the ear with the received speech from the loud-
speaker and may interfere with reception.

Greater appreciation of quietness, and the use of
modern sound absorptive materials in office and
home construction have made rooms having good
acoustical properties quite prevalent. A recent field
survey, in a business area, shows that a high per-
centage of Speakerphone installations are in private
offices having good acoustical properties. In these
offices, the Speakerphone generally provides satis-
factory telephone service with the benefits of hands-
free telephony and permits a small group to par-
ticipate in the conversation.

W. F. CLemency joined the Research Department of the Western Electric
Company in 1923. He was engaged in studies of transmitter carbon and in the
development of improved methods of manufacturing this carbon. Since the
incorporation of the Laboratories, he has been a member of the Apparatus
Development Department and has worked on the development of telephone
transmitters, receivers, and other electro-acoustical devices. He is now engaged
in the application and development of loudspeaking telephone sets. Mr.
Clemency received a degree in Electrical Engineering from Brooklyn Poly-
technic Institute in 1934,

As modern electronic equipment is called upon to perform increasingly intri-
cate operations, electrical signals must frequently be delayed within a circuit.
Since electromagnetic waves travel at a speed of more than 186,000 miles
per second, most methods of providing such delay require considerable
space or equipment, Recently, however, Bell Laboratories has been develop-
ing ultrasonic delay lines which occupy a relatively small space, and can
provide time intervals ranging from a fraction of a microsecond to several

Time delay of electrical signals is useful in many
Bell System communication circuits, Such delay is
needed, for example, to produce series of pulses
accurately spaced in time for various coding sys-
tems. Another general field of application is in
storage devices wherein an electrical signal is
stored for use at a later time, as in electronic
computers,

It has been found that ultrasonic delay lines pro-
vide a convenient method of providing these delays
in a relatively small space. In such a device, time
delay is achieved by converting an electrical signal
into an acoustical wave, which is propagated along
a suitable path and then reconverted to an electrical
signal, These delays can range from a fraction of a
microsecond to several thousand microseconds, and
for these, bandwidths of from three to six mega-
cycles are easily obtainable. Since frequencies in
the megacycle range are usually employed, the
name “ultrasonic” is applied to these devices,

Ultrasonic delay lines were developed during
World War II for use in radar systems, and H. J.
McSkimin of the Laboratories’ Mathematical Re-
search Department has made valuable contributions
to their theory and design, Because of their inherent
accuracy and wide-band characteristics, these ultra-

sonic delay lines provided a convenient means of
producing series of accurately spaced pulses for
radar range calibrations. Long delay lines of this
type were also essential to the development of
moving target indicators for radar systems, and
short lines are now being used in various coding
systems for assuring communication privacy.

Other methods of delaying an electrical signal
involve transmitting an electromagnetic wave in a
coaxial cable or an electrical network and hence
require much more space. A video delay of 10
microseconds, for example, would require 6,480
feet of ordinary coaxial-cable, 16 feet of specially
constructed ‘delay cable,” or an electrical network
occupying 56 cubic inches. The same delay with
equivalent bandwidth can be provided by an ultra-
sonic delay line only 1.48 inches long. Acoustic
waves travel some 100,000 times slower than electro-
magnetic waves, and therein lies the space advan-
tage over electrical delay lines.

A simple delay line consisting of two transducers
and a delay medium is illustrated in Figure 1(a).
The transducers in this device convert electrical
signals into mechanical stresses, or vice versa, by
the piezoelectric effect. The mechanical stress ap-
plied to the delay medium travels through a pre-

A single-ended delay line is a simple rod with
a transducer on one end. The signal travels the
length of the rod, is reflected, and travels back to
the transducer where it produces a delayed pulse.
Some of the energy is reflected at the transducer,
however, and again travels twice the length of the
rod before producing a second output pulse. Thus,
in response to a single input pulse, a series of
equally spaced pulses are produced which can be
used for time calibration purposes. In a double-
ended delay line with two transducers, as in Figure
l(a), the signal travels the length of the rod only
once and produces only one output pulse de layed
in time with respect to the input pulse. Any signals
arising from reflections at the transducers are, in
this case, unwanted responses, and efforts are made
to suppress them. To conserve space for longer
delays, the transmission path can be folded so that
the ultrasonic wave hits one or more reflecting
faces before arriving at the output transducer.
Delay lines of this kind are called multiple reflec-
tion types.

The transducers are most efficient over a fre-
quency band near their resonant frequency, and
bandwidths of about 30 percent of the center fre-
quency can be realized. To provide sufficient band-
width for delaying video signals, this center fre-
quency must be 10 me or higher. A carrier fre-
quency, equal to the transducer resonant frequency,
is modulated by the video signal to be delayed, This
modulated carrier signal is applied to the input trans-

Fig. 1 — Typical simple delay line configurations:
(a) rod type; (b) single reflection type; (c) triple
reflection type.

ducer of the delay line, and the signal appearing at
the delay line output can be demodulated to re-
cover the original video information.

The transducers can be either crystalline materials
having intrinsic piezoelectric properties such as
quartz crystals, or non-crystalline materials made
to have these properties by a polarization process,
as in the case of barium titanate ceramic. For delay
line applications, a solid medium is preferred to a
liquid because of its mechanical stability and sim-
plicity. The solid used almost exclusively because
of its low attenuation, is vitreous silica, an optical
grade of fused quartz. Vitreous silica has a tem-
perature coefficient of delay amounting to about
100 parts per million per degree centigrade, and
hence for some applications the delay line must be
temperature controlled,

waves or transverse waves. In longitudinal waves
the particle motion is along the direction of propa-
This is the type of wave transmitted by

Fig. 2 The three units at
the left correspond to the type illustrated in Fig.
l(a), the unit being held corresponds to the type
shown in Fig. 1(b), and the unit at the right cor-

gases and liquids which gives rise to the sensation of
sound, Solid materials, however, can transmit not
only longitudinal waves but also transverse waves
—waves which the particle motion is perpen-
dicular to the direction of propagation. Transverse
waves are similar to light waves in that they can
be polarized; that is, they can be arranged so that
all particle displacements lie in the same plane. In
general, when either a longitudinal or transverse
wave is reflected at a solid-air interface, the re-
flected wave has two components, one longitudinal
and the other transverse
of reflection.

each with a different angle
For the special case of transverse
waves polarized perpendicular to the plane of

FREQUENCY IN MEGACYCLES PER SECOND
Fig. 3— Frequency response of a 25-microsecond

delay line using barium titanate transducers ter-
minated in a 62 ohm load. The spurious response
in this unit is 20 db below the main response.

Fig. 5 — Configuration of a 990-microsecond delay
line containing 30 reflection paths,

cidence, the incident wave is totally retlected as a
transverse wave with the angle of reflection equal
to the angle of incidence. Hence, this type wave is
used for delay lines that require many reflections.

clusively up to the present time, can be so oriented
as to produce either longitudinal or transverse
waves. Delay lines constructed with quartz crystal
transducers are characterized by a relatively low
capacitance and a high characteristic impedance,
hundreds to thousands of ohms. Because of the low
coupling of quartz crystals, such a delay line must
be terminated in a low impedance in order to obtain
a 30 per cent bandwidth, This results in a delay
line of high loss, some 30 to 50 db. The recently
developed barium titanate ceramic transducer, how-
ever, has a much higher coupling, which enables
the construction of delay lines of 30 per cent band-
width with much lower loss. The loss ranges from
6 to 20 db when the line is terminated near its
characteristic impedance, which is a low value of
30 to 100 ohms. The transducer capacitance is high,
400 to 800 micromicrofarads. For practical reasons,
the barium titanate ceramic transducers cannot be
polarized readily for generation of transverse waves,
and their use is therefore limited to designs based on
the use of longitudinal waves.

From the preceding discussion, it might appear
that it would be desirable to use polarized trans-
verse waves in all designs because of their simple
reflecting properties. However, for low-loss appli-
ations it is of great advantage to use barium titanate
ceramic transducers because of their high coupling,
and for this reason longitudinal wave types are used
wherever possible. The performance of designs
using longitudinal waves is good, provided the angle
of reflection and the number of reflections are kept
small. Hence, the designs illustrated in Figures 1(b)
and l(c), while feasible for transverse waves, are
also good designs for longitudinal waves, and the
low-loss barium titanate transducers can be used
in this application.

Some typical short delay lines are shown in Fig-
ure 2. At the left are three variations of the single
rod type with transducers on both ends as dia-
grammed in Figure l(a), One of the transducers
can be seen as a light disk soldered to the end-face
on each of these units. The solder is allowed to
flow over the entire end-face to act as an absorber
for end-to-end reflections. The other transducers
are mounted on the opposite end-faces not visible
in Figure 2. The light areas on the other faces of
the second, third, and fourth units from the left are

fired silver electrodes for the electrical ground con-
nections. They are insulated from each other by the
uncoated area appearing as a dark grey band passing
around the rod, as in the second unit. The other
electrical connection is made to the electrode on
the exposed face of the transducer.

Single-rod type designs are useful for delays in
the 1 to 5 microsecond range. For the 5 to 25 micro-
second range the single reflection pattern of Figure
l(b) is used. In these units, the transducers are
mounted on faces making equal angles with the far
end so that an input at one transducer is reflected
at the far end and arrives at the output end on a
path perpendicular to the output transducer, An
example of this type is shown in Figure 2. Here
both transducers are visible on adjacent faces. The
grey strips in the light silver coated areas are again
uncoated areas to isolate the grounding electrodes,
For still longer delays, up to about 100 microsec-
onds, the three reflection pattern of Figure 1(c) is
used. Here both transducers are located on the
same face, and the beam is reflected from a tilted
face at the opposite end back to the center of the
transducer face. From there the path is symmetrical,
going to another tilted face and then to the output
transducer. A delay line of this type is shown at
the right in Figure 2. On this unit, solder has been
added to the silvered electrode areas to act as an
absorber for energy striking the major faces.

Typical delay-line performance is shown by the
bandwidth curve in Figure 3 for units with delays
up to about 25 microseconds, This design has a 4.8-
mec bandwidth centered at 14.8 me with a mid-band
loss of 5.5 db. Spurious responses, due to end-to-end

Mrs. M. S. Libby engaged in bonding a
transducer to an ultrasonic delay line.

reflections or reflections from the sidewalls, are kept
at least 20 db below the main response. For units
of this design using longitudinal waves, the path
length is 0.235 inches per microsecond of delay,
and for the rod type the cross section can be as
small as % inch in diameter.

For delays greater than 100 microseconds, pat-
terns containing many reflections are necessary to
save space. Properly polarized transverse waves are
used in these applications because of their afore-
mentioned reflecting properties, and because of
their lower velocity. The path length is 0.148 inches
per microsecond of delay, The “double-wedge” re-
Hection pattern of a 500 microsecond delay line is
shown in Figure 4. In this design, a beam is re-
flected back and forth between the two faces that
form a wedge until it is finally reflected back on
itself and returns to the input end. There, it strikes
a turning face that sends it into another wedge at
right angles to the first. Part of the ultrasonic beam
actually spreads beyond the geometric path out-
lined by the shaded areas in Figure 4, This part of
the beam follows undesired paths through the delay
line, some of which terminate at the output trans-
ducer. These give rise to unwanted signals occurring
at times other than the designed delay value. How-
ever, with 20-mc transducers, the geometry of the
double wedge, having a relatively open pattern near

the transducers, produces good unwanted response
performance of 40 db below the main response for
the 500 microsecond size.

A more compact design used for a 990-microsec-
ond delay line is shown in Figure 5, where 30 re-
flections are used to fold twelve feet of path into
a polygon 5% inches in diameter. Starting at trans-

line using quartz crystal transducers terminated in
a 500 ohm load. The unwanted spurious response
in this unit is 34 db below the main response.

ducer X, the beam tollows the reflection pattern in
numerical order and finally arrives at the output
transducer on path 31. This is one of the most com-
pact designs consistent with good unwanted re-
sponse, about 34 db in this case. A typical band-
width curve for this design using quartz crystal
transducers is shown in Figure 8. Such a delay line
would be packaged in a hermetically sealed con-
tainer, which would result in a total weight of 5
pounds, 10 ounces.

By suitably scaling up the dimensions of the
polygon, longer delays can be attained—up to
3,300 microseconds. This limit is established by
the largest available disk of vitreous silica, which is
17 inches in diameter. Recently, some experimental
2,000-microsecond units have been built.° Although
the loss and bandwidth are similar to those in the
990-microsecond design, the unwanted response is
improved to 38 db, due in part to the larger re-
flecting surfaces.

* The photograph at the head of this article shows the
author testing an experimental 2,000 microsecond unit.

May, Jn., received the B.A. degree in physics from Wesleyan Uni-
Navy, where he was engaged

in the deve ‘lopment of radio-controlle d aircraft and sidtiome radar, followed by
two years at the Naval Research Laboratory, Boston Field Station, in the devel-
opment of ultrasonic delay lines, He received the M.A. degree in physics from
Tufts College in 1949 and in 1952 received his Ph.D. degree in physics from

Yale University, publishing a thesis on nuclear physics research with the Yale
cyclotron, Mr, May became a member of Bell Telephone Laboratories in Octo-
ber r, 1952, where he has been concerned with fundamental studies of ultrasonic
delay lines, He is a member of Sigma Xi, Sigma Pi Sigma, the Institute of Radio

Dr. Claude E. Shannon, research mathematician
in charge of Communication Theory, Discrete Sys-
tems and Special Research at the Laboratories, was
elected a member of the National Academy of Sci-
ences at its 93rd annual meeting held in W ashing-
ton, D. C., on April 24. Dr. Shannon, serving now
as a visiting professor of electrical communications
at Massachusetts Institute of Technology, has been

The National Academy of Sciences is a private,
non-profit organization that is restricted to 600 mem-
bers. Other members from Bell Laboratories in-
clude President M. J. Kelly, Executive Vice Presi-
dent J. B. Fisk, and J. R. Pierce, Director of Re-
search, Electrical Communications.

Some years ago, the 555 PBX switchboard® was
developed to fill the particular requirements of a
number of telephone customers. The design was
pointed toward flexibility of equipment, ease of
maintenance, adequate range for trunk and station
facilities, and low power consumption. One feature
of the switchboard was the replacement of lever-
action keys by push buttons for ringing and less con-
ventional “push or turn” keys for the usual PBX
functions. All cords, lamps, and ringing push but-
tons are mounted on a sloping shelf, leaving the op-
erator’s desk free for writing or other work. The
“push or turn” answering keys are mounted on the
vertical face of the board, below the sloping shelf.

To answer a call, the operator turns the key
handle to the right where a detent holds it in posi-
tion until it is restored to the normal vertical posi-
tion. For a “through-dial” or night connection, the
key is pushed in toward the face of the board where
it is also held by a detent. Locks are provided so
that when the handle is turned, it cannot be pushed
in, and when pushed in, it cannot be turned.

Experience indicated that some modifications of
the key handle would add to the operator's comfort
and to her efficiency. Suggestions were made to (1)
remove the slight projection at the end of the handle
since this projection partially masks the white ref-
erence line, making it difficult to see, and also offers
some discomfort to the fingers when operating the
key; (2) enlarge the “pushing” area and increase
the radius around the edge; and (3) provide a suit-
able indicator for the “in” and “out” positions, since
the black handle against the black key-shelf makes
the position difficult to determine.

These comments were taken into consideration
when the new handle was designed. Figure 1 shows
the original handle along with the new version.

The projection, indicated on the original handle by
the pencil, has been removed and all edges are
rounded. The lever part of the handle is longer,
offering a better grip, and blends into the pushing
area so as to provide a large smooth surface, The
white reference line is longer and wider for in-
creased visibility, and is no longer masked by the
projection. The pushing area is larger, tapering
toward the back to provide a grip for pulling when
the pushed-in key is restored to normal.

Alternate black-and-white stripes at the back of
the handle serve as a “flag” to indicate the position
of the key. When the lines are visible in front of the
key-shelf, the handle is free to turn. When it is
pushed in for “through-dial” service, the lines dis-
appear, indicating that it cannot be turned. These
handles are being regularly supplied on new switch-
boards and are available separately for replacement
in existing switchboards.

Not only is Bell Telephone Laboratories concerned with developing new sys-
tems and devices for improving telephone service, but it is also constantly
endeavoring to improve components in the existing equipment, One im-
portant aspect of this work deals with fundamental research aimed at ex-
tending the useful lifetimes of relay contacts. The many millions of such
contacts used in telephone central offices throughout the country make them
a significant item in the maintenance costs of the Bell System.

Telephone switching systems depend upon the
reliable operation of a large number of relay con-
tacts. Many of these carry relatively large currents
~about one-half ampere — and operate relatively
frequently. They are subject to an erosion of the
contact metal, which severely limits their useful
lifetimes, This erosion is primarily due to electrical
arcing, and hence satisfactory contact lifetimes can-
not be achieved unless the energy dissipated in ares
on make and break is limited to a small fraction
(about one ten-thousandth) of the energy stored
in the inductance of the usual relay loads.

From work on electrical breakdown in gases it
was believed about ten years ago that there can be
no electrical breakdown, and therefore no arc, unless
the potential difference between electrodes is above
a certain “minimum sparking potential” which is
roughly 300 volts for air. Very early work per-
formed about 1901 gave evidence to the contrary,
but this had apparently not been incorporated into
recent literature. Thus, until a few years ago, one
expected that there might be arcs at the breaking
of contacts in an inductive circuit, but that there
could be no discharge at all on closure with po-
tential differences less than 300 volts. Neverthe-
less, experimenters in the field of contact erosion
were aware that arcing occasionally takes place on

the closure of contacts when the potential difference
between them is only 48 volts. This was explained
by assuming that small projections on the surface
touch first and that the resulting current evaporates
the points of contact with explosive violence, initi-
ating an arc in the hot vapor.

Oscilloscopic studies at Bell Telephone Labora-
tories revealed no evidence to indicate that con-
tacts touch preceding arcs on closure, and one is
led to conclude, in agreement with the very early
work, that arcs occur before there is any metallic
contact. Furthermore, consideration of the proc-
esses expected to take place when contacts close
at voltages considerably above the ionization po-
tential of the atoms of contact metal (around
10 volts), but below the minimum sparking poten-
tial for air, indicates that a new type of breakdown
process will take place. Even for a very low poten-
tial difference, the electric field between approach-
ing contacts necessarily becomes extremely high.
When the field at the negative electrode, or cathode,
becomes great enough, in the neighborhood of ten
million volts per centimeter, both theory and experi-
ment show that appreciable current must flow from
the cathode. This “field emission” current is not
in itself a “breakdown,” but is the first step in the
breakdown process.

Field emission current is extremely sensitive to
small changes in the field, so that small regions of
the cathode surface, where the field is somewhat
above average, will deliver nearly all the current.
Because no metal surface can be perfectly smooth,
projections on the cathode provide such regions of
increased field. The flow of the field emission cur-
rent, through the resistance offered by the small
points, heats the projections from which the current
is drawn. A slightly larger region of the positive
electrode, or anode, is heated also, in this case by
electron bombardment.* When the heated region —
either of the anode or of the cathode — reaches the
boiling point of the contact metal, the density of
atoms and molecules in the gap is increased, so that
each electron now experiences a greater number of
collisions in crossing the gap. If the electron energy
is above the minimum ionization energy of the
atoms in the gap, ionization will take place, creating
ions and new electrons. These electrons are quickly
drawn out of the gap, leaving behind the relatively
massive and slow-moving positive ions. The pres-
ence of these ions increases the electric field at the
cathode surface, which results in greater field emis-
sion current. The increase in electron current in-
creases the amount of ionization, and the process
rapidly builds up to a “breakdown”; that is, the
current increases until it is limited only by external
circuit elements. From an analysis of this process
it has been shown that a number of ions equal to

* The electrons do not spread a great deal in crossing the
contact gap, because in the range of voltage under consid-
eration the distance at which appreciable field emission
appears is less than 10°* cm. Each electron experiences only
one or two collisions with gas molecules in this distance.

(1) (2)
Anode Cathode
Ares Ares
1. Anode Appearance Hole Nothing
(Fig, 2, left) (or shallow hole)
2. Cathode Appearance Roughened Scratches

3. Occurrence:
voltage above 400 Never Always
voltage below 300 Sometimes Sometimes
4. Weld Frequently Never
5. Are voltage about 11 about 16
volts volts

only a few percent of the number of field emission
electrons is more than sufficient to cause break-
down, and that the elapsed time from the first
measurable currents to the completion of the break-
down is too short to be detected by oscilloscopic
observations.

Detailed experimental confirmation of the break-
down process just outlined is difficult in air, because
one does not expect this process to be effective
above the minimum sparking potential (approxi-
mately 300 volts), and at lower voltages the times,

Fig. 1 — (a) Oscillogram of a sustained are on
break followed by an open circuit, Starting from
the left, the contacts are closed at first and the
trace is a horizontal line at zero voltage. The con-
tacts then open into an are at 15 volts which lasts
for about 300 microseconds, When the are goes out,
the voltage jumps to a new value, then charges up
more slowly because of the current from the ex-
ternal source. (b) “Showering” on break followed
by a glow discharge. After the portion of the trace
at zero voltage, there is a region of rapid charge-ups
and breakdowns lasting for about 30 microseconds.
This is followed by a steady glow discharge at 300
volts lasting for about 70 microseconds, When the
glow discharge goes out, the voltage begins to fall
as the capacitance discharges through the power
source, which supplies only 50 volts.

spacings, and pre-breakdown currents are extremely
small, Furthermore, the effects of dirt and oxide
films are difficult to estimate. Each step in the pro-
posed process, however, is also operative in a
vacuum, Experiments have been carried out in high
vacuum, and the evidence gathered confirms the
theory of breakdown caused by field emission en-
hanced by ionic space charge.

Breakdowns of this type may take place either on
closure or break of telephone contacts. Depending
upon the circuit and the condition of the metal sur-
faces the arcs which follow breakdown may last
for many microseconds and be easily observable on
an oscilloscope, or they may be so brief as to be
unresolvable, leading to many rapid cycles of charg-
ing up and breaking down of local capacitance. This
latter condition is called “showering.” It is during
these periods of either continuous arcing or show-
ering that most of the damage to relay contacts
takes place. Typical oscilloscope traces of the volt-
age across electrical contacts in these two forms of
discharge are reproduced in Figure 1.

Knowing thé conditions which lead to arcs on
make and break is a promising start in the predic-
tion of the useful life of relay contacts. However,
attempts to understand quantitatively the amount
of metal transferred by arcing at contacts have fre-
quently been frustrated in the past by inconsistent
and contradictory experimental results. A consid-
erable step toward understanding erosion was made
by discovering, in experiments performed on palla-

Typical cathode mark due to a single
“cathode” arc. There is frequently no mark at all

dium contacts, that there are two distinct types of
arcs. One type, called the “anode” arc, leaves a
melted crater on the anode surface and a roughened
cathode spot. The other, called a “cathode” arc,
leaves many tiny melted spots on the cathode, usu-
ally along scratch lines when the cathode is a pol-
ished surface, and little or no mark on the anode.
Photomicrographs of the damage done to anode
and cathode surfaces in single typical arcs of the
two types are shown in Figures 2-4. One might
expect, from examination of these photographs, that
an anode arc transfers metal from anode to cathode,
and a cathode are from cathode to anode. These

- (Left) Photomicrograph of a typical anode pit due to a single “anode” arc. Magnification

2000 diameters, (Right) typical cathode mark due toa single “anode” arc. Magnification 2000 diameters.

Fig. 4— Electron micrograph of a portion of the
cathode mark due to a single “cathode” arc. Magni-
fication 47,000 diameters,

expectations have been confirmed both by deter-
mining the transfer occurring in single arcs of each
type by radioactive tracer methods, and by weigh-
ing on a microbalance after many closures under
circumstances known to produce predominantly one
or the other type of are.

To understand contact erosion and to predict con-
tact lifetimes, it is thus necessary to understand the
factors affecting the occurrence of the two types of
arc. In general, for striking voltages above 400
volts, only cathode arcs occur, and the probability
of occurrence of anode ares increases as the voltage
is lowered, Cleanliness of the cathode surface favors
Fig. 5 — Oscillograms of arcs on closure discharg-
ing 200 feet of 50 ohm cable charged to 200 volts.
Trace length is 0.8 microseconds, (a) Are followed
by a “weld”. (b) Are followed by an open circuit.
There is also a trace at zero voltage.

It is now believed that, on clean surfaces, a
cathode are follows a breakdown initiated by the
evaporation of a small projection on the cathode
by resistive heating. An anode are occurs when the
cathode projection is so large that the anode reaches
the boiling point before the cathode projection. In
the cathode arc, metal vapor necessary for the are

Photomicrograph of an anode pit due to
discharging a cable where the are has gone out and
has been re-ignited. This is to be compared with
the left part of Figure 2, where the are did not
strike a second time.

is supplied by the cathode, but in the anode arc it
is supplied by both electrodes with the larger frac-
tion coming from the anode. Some of the distin-
guishing characteristics of the two types of arcs are
shown in Table 1.

A further complication in the prediction of con-
tact erosion is due to the occurrence of “welds.”
Anode arcs are frequently terminated before the
circuit is discharged, by short-circuiting the con-
tacts by molten metal from the anode spot. Oscil-
loscope traces of arcs which do and do not termi-

nate in welds are shown in Figure 5. When welding
occurs, the erosion depends upon the time of weld-
ing as well as upon the relative numbers of the two
types of are,

The problem of time of welding should properly
be considered together with other phenomena that
occur at the termination of the arc. In general,
neither type of arc can persist when the current
falls to indefinitely small values. Observed “mini-
mum are currents” are of the order of 0.3 to 1.0
ampere for both types of are on clean metals. The
reasons for this minimum are poorly understood for
cathode ares, but for anode arcs it appears that the
anode spot grows with time, and thus the power
necessary to maintain the surface at the boiling
point also increases. When the current is no longer
sufficient to supply this power, the arc goes out.
Since the size of the anode spot depends on the
course of the current up to the time of extinction,
the minimum arc current is a function of the his-
tory of the arc up to that point. When an arc is
extinguished, the electric field at the anode, which
was very small during the arc, is suddenly increased
and the pool of molten metal is pulled toward the
cathode. Thus, welds occur most frequently at the

end of the growth of one of the anode spots when
the are is extinguished. If the circuit is still capable
of delivering considerable current, however, the
weld may be blown up and the are reignited. The
nature of an anode pit when a second arc strikes
in discharging a cable is shown in Figure 6. If the
pool of metal in the anode spot is either too small
or cools too quickly, the anode metal may not be
sufficient to bridge the gap, and the anode arc may
end in an open circuit, just as do all cathode ares.
Although the results of many tests are under-
stood as described, it is not possible to predict con-
tact life with great reliability. In view of the ob-
served dependence of the erosion upon atmospheric
conditions, upon the previous history of the con-
tacts, and upon small changes in circuitry, it is dif-
ficult to believe that operating conditions can ever
be sufficiently well specified in a reasonably concise
manner to make such predictions possible. Never-
theless, certain conditions favorable to long lifetimes
are understood. They involve, among other things,
avoidance, where possible, of the injurious organic
vapors, prevention of the discharge of any consid-
erable capacitance on closure, and keeping the
energy stored in the load inductance to a minimum.

Paut Kisiiuk received a B.S. degree in chemistry from Queens College,
New York City, in 1943. After three years in the armed forces, during which
he was engaged in maintenance of repeater and carrier telephone equipment
for the Signal Corps overseas, he resumed his education at Columbia Univer-
sity. He received an M.A. degree in physics in 1947 and a Ph.D. degree, also
in physics, in 1952. Mr. Kisliuk joined the staff of Bell Telephone Laboratories
in 1952, and is a member of the Physical Research Department, where he
has been engaged in research in contact physics. He is a member of the
American Physical Society and of Sigma Xi.

A. G. Jensen, Laboratories Director of Television
Research, was recently elected a Fellow of the
British Television Society in recognition of his out-
standing contributions to the development of tele-
vision. The Television Society, founded in 1927,
is “the first society in the world for the furtherance
of research in television and allied problems.”

Mr. Jensen has received a number of other honors
for his work in television research including the
David Sarnoff Gold Medal from the Society of
Motion Picture and Television Engineers, and the
G. A. Hagemann Gold Medal for Industrial Re-
search from the Royal Technical College in Copen-
hagen, Denmark.

The Centralized Automatic Message Accounting system serves many local

telephone offices by recording information on calls outside the customer's
local dialing area. In a CAMA installation, trunks from the local offices are

periodically tested by a circuit which helps insure service that is free of inter-
ruption or other difficulty. Operation is automatic and does not require
assistance from maintenance personnel in the local offices.

The Centralized Automatic Message Accounting
system has required the development of several
new circuits and the adaptation of many earlier
units.* This equipment is installed in a centralized
location (a crossbar tandem office), so that it can
serve a large number of surrounding local offices.
With the CAMA feature, customers can dial many
extended-area and long-distance calls even though
the cost of installing separate Automatic Message
Accounting equipment in each local office is pro-
hibitive. The service is much like the previously
developed AMA operation, except that after the
customer has dialed his number, a special CAMA
operator asks for the originating telephone number.
Otherwise, the recording of information relative
to the telephone call is entirely automatic.

Between the crossbar tandem office and the sur-
rounding local offices there are a large number of
pairs of wires which are used for the transmission
of telephone conversations, and which are usually
referred to as “trunks.” More exactly, however, a

“trunk” consists of the pair of wires plus the relay
circuits at each end. At the tandem office, such a
trunk relay circuit must perform many functions:
it must work with other parts of the crossbar switch-
ing system to set up the connection to the called
telephone office, and it must later take charge of
the connection and maintain it until appropriate
In the CAMA
system it must also perform several tasks in asso-
ciation with the AMA recording equipment.

Described here is an automatic test circuit that
tests all the operations of the trunk relay equip-
ment connected to a cable pair on a call coming
in from a local office. The wide variety of tests
performed, and the rapidity of operation, make
this test circuit a very valuable part of the com-
plete CAMA installation. As will be seen later,
much of this value derives from the fact that, in the
tandem office, maintenance personnel do not need
to ask for assistance of the various local offices in
arranging for or conducting the tests.

In Figure 1, the automatic test circuit is repre-
sented in the shaded portion of the block diagram,
and the other units are those parts of the CAMA

system and the crossbar tandem office with which
the test circuit is concerned, The trunk relay equip-
ment to be tested is represented in the upper left
corner of the diagram, What happens on a regular
service call is briefly this: the originating customer
at the left is connected through the crossbar tan-
dem office via the incoming trunk relay equipment,
and during the progress of the call this trunk cir-
cuit performs the tasks that have been mentioned.
The function of the test circuit is simply to simu-
late, in as exact a manner as possible, an actual
service call as dialed by a customer, and to observe
whether the trunk circuit is performing properly.
Conditions applied to the trunk circuit during the
simulated call are more severe than those usually
encountered in service. The test circuit, however,
does not automatically test transmission (that is,
the transmission characteristics of the voice path),
nor does it request the services of the CAMA
special operator.

Local offices send called-number pulses in sev-
eral different ways, termed Panel Call Indicator
(PCI), Dial (DP), and Multifrequency (MF)

pulsing. At the present time, the test circuit simu-
lates the panel call indicator and dial pulse types
of calls, and the multifrequency type is to be added
later. The test circuit recognizes the type of trunk
circuit it is to test, and alters the test procedure
accordingly. It contains generators for producing
both the panel call indicator and dial pulses.

In terms of the called-number pulses and other
types of signals, the test circuit is thus a simulated
originating office. It is also a simulated terminating
office because the outgoing or destination trunk
used is actually a “return test line,” which has as
its destination the test circuit. Signals that the ter-
minating office sends back to the tandem office are
by this means also simulated, and the effects on the
incoming trunk circuit observed.

Certain tests are made as the trunk circuit re-
sponds to the normal sequence of events of a simu-
lated telephone call. The test circuit tests the ef-
fects of “answer” and “disconnect” signals as they
are normally received from the terminating office.
The effects of “seizure” and “disconnect” signals
from the originating office are also tested. In addi-

ORIGINATING | |
OFFICE l CROSSBAR TANDEM OFFICE | TERMINATING OFFICE
|
| yest | — | + +—
LINK | SENDER MARKER | EQUIPMENT
|
--
| H INDE XER
\
LINE
| CONNECTOR ANO |
| ; ;
INCOMING |
TRUNK RESERVE TRUNK |
| OUTPULSING
vast CIRCUITS |
| SEQUENCE |
| CONTROL
TESTS |
SEM! ~AU TOMATIC
| Tests: |
| THROUGH |
AUTOMATIC TRANSMISSION
TR K TEST
—
| INDICATOR
| DISPLAY |
Fig. 1. — Block diagram showing the automatic trunk-test circuit and its association with CAMA crossbar

tandem equipment; test circuit acts as a simulated originating and terminating office.

corder circuit at the time the entries are made.
The test call places a special non-billable entry on
the AMA paper tape.

All these operations are performed in testing a
single incoming trunk circuit. If no trouble is found,
another trunk will be selected automatically, and
the test circuit will proceed in this manner through
all the incoming trunk circuits in the office. Trunk
circuits that are busy with actual telephone calls
may be passed by and tested later when they are
idle. If trouble is encountered, te sting will stop
and an alarm will sound. An array of lighted lamps
indicates the point at which the test was blocked,
which is evidence of the nature of the trouble.

Potomac Telephone Company at trunk-test circuit
connector frame in Washington, D. C., installation.
ROM
TOMER
—
tion, extra tests are inserted between these normal Panera heme
events. For example, the way the trunk responds to ET AES
a busy signal is tested while the trunk is waiting ee eee
for the simulated call to be “answered.” il
TANOEM TRUNK FA Ties
Several additional tests performed by this circuit Ba !
SWITCHES NG, ar - —
should also be mentioned. Under certain circum- &
stances, when a first attempt to establish a tele- i; -- rauNe
phone connection is unsuccessful, a second trial Tare Bu57 /

The test circuit determines whether the trunk cir-
cuit properly handles such requests for a second (b) OF TRUNK USING "MAKE BUSY" CIRCUIT

trial. It also checks that there are no trouble con- Fig. 3— Two types of trunk connections between

ditions on the outgoing leads of the trunk circuit,
and connects other leads into the trunk circuit to
observe the performance of individual relays. Cer-
tain relays must operate and release within speci-
fied time intervals, and the test circuit checks such
timing characteristics. Also, the test circuit deter-
mines whether the incoming trunk circuit is able
to cause the proper recording of entries on the paper
tape of the Automatic Message Accounting equip-
ment. This is done by a test connection to the re-

local and tandem offices; both are transferred
without assistance from the local telephone office.

ful in checking some of the office wiring which pro-
vides information necessary for routing the call and
determining the charges.

Some of the interesting aspects of the new cir-
cuit are the features associated with the transfer of
When a trunk

must be made that customers will not be denied
service by having their calls run into a “dead end.”
This is commonly done by making the trunk appear
busy; that is, personnel at the originating local of-
fice arrange the originating trunk circuit on that
end of the cable pair to appear busy to all calls.
In this way, calls are diverted to other trunks dur-
ing the test procedure. Such manual “make-busy”
arrangements at the originating end are not prac-
tical when an automatic test circuit is located at
the tandem office.

This problem is solved in two different ways, as
illustrated in Figure 3. The first method has to do
with originating offices (crossbar or panel) that
use the PCI type of out-pulsing. As seen in Fig-
ure 3(a), the incoming telephone call is in this case
diverted to a “spare” or reserve trunk circuit, the
transfer being accomplished automatically at the
crossbar tandem end of the connection. The re-
serve trunk circuit is a duplicate of the incoming
trunk circuit; it is associated with test circuit identi-
fication circuits which provide the same rate-class
(charging) and class-of-service (routing) informa-
tion as with a regular trunk circuit normally serving
a particular cable pair. Arrangements are also
made that if the testing of the regular trunk circuit
ends before the end of the customer’s call, the trans-
fer condition is maintained as long as the reserve
trunk is busy. Under this management the customer's
call will not be interrupted if the test being con-
ducted ends before he is finished.

A second method of diverting customer calls is
applied when the originating local office (step-by-
step switching equipment) uses the DP type of
outpulsing. This is illustrated in Figure 3(b).
Here, outgoing trunk circuits in the originating
step-by-step offices are arranged so that the test cir-

cuit in the crossbar tandem office can make them
appear busy. Calls are therefore diverted to other
trunk circuits in the originating office, and no re-
serve trunk circuits in the crossbar tandem office
are needed in this case. As with the previous method
of transfer, the arrangement here permits automatic
control by the test circuit in the crossbar tandem
office, and thus eliminates the need for manual as-
sistance in the originating office.

As mentioned earlier, the test circuit proceeds
methodically through the incoming trunk circuits
in the crossbar tandem office. Now, if a faulty trunk
circuit is detected, a feature is provided to hold
it out of service for subsequent maintenance action.
On the key and lamp panel of the test circuit, there
are a number of trunk-hold-busy (THB) keys.
With these keys faulty trunks detected by the test
circuit can be held out of service pending mainte-
nance action, meanwhile permitting the test cir-
cuit to test other trunks. A THB key is associated
with the trunks of one AMA recorder. Operation
of the key after one of the trunks has been seized
by the test circuit will lock that trunk to the key.
The test circuit busy test insures that only idle
trunks can be thus taken out of service. If further
testing of the transferred trunk is required, the test
cire*t can automatically scan all trunks associated
wit . a particular THB key and locate the trans-
ferred trunk. The trunk may be released from its
locked-in condition at any time merely by restoring
the associated THB key.

The test circuit can automatically test 2,000 in-
coming trunk circuits, a capacity that is an im-
portant factor in the economical maintenance of
continuous service to customers. A significant part
of the economy is derived from the elimination of
the need for manual make-busy arrangements.

in 1948, and he joined the Laboratories in the same year as a student in the
Communications Devleopment Training Program. Rotational work assignments
performed as part of that program included duties in the Switching Apparatus
Development Department and in the Transmission Development Department.
Since 1949 he has been in the Switching Development Department where he
has worked on switching circuit design, first for the Automatic Message
Accounting Center and then for the Tandem Office CAMA project. Later he
worked on the design of a portable traffic usage recording circuit and recently
has joined the group assigned to the toll office CAMA project. Mr. Dusenberry
is an Associate Member of the American Institute of Electrical Engineers and
is a member of Tau Beta Pi and Phi Beta Kappa.

Tactical military communication has recently been much improved by the
Laboratories’ development of a light-weight system for transmitting twelve
telephone conversations over a single four-conductor cable. Two types of
repeaters have been developed to restore signal strength and permit the
terminals to be placed as much as 200 miles apart.

As a part of the development of a twelve-channel
cable carrier telephone system for the military,°
two types of repeaters were designed. The first of
these is officially designated Telephone Repeater
AN/TCC-11;, it operates without attendance by per-
sonnel. The other is an attended repeater, officially
designated Telephone Repeater AN/TCC-8. Both
units, like all the equipment used in the complete
system, were designed to achieve a minimum in
weight and a maximum in performance. The equip-
ment thus represents a great improvement over
previous tactical military carrier telephone com-
munication systems. The unattended repeater in par-
ticular contains some interesting and unique fea-
tures, and a description of these will comprise most
of this article. The attended repeater is more con-
ventional in design and will be described in some-
what less detail.

A photograph of the unattended repeater is shown
in Figure 1. These repeaters are normally spaced at
5&-mile intervals along the cable to amplify signals
in the frequency range from 12 ke to 99 ke. The gain
or amplification of the repeater is equalized to com-
pensate for the attenuation of a 5%-mile cable span
at all frequencies in the 12 to 68 ke (message and
pilot) range. In addition, the repeater gain is auto-
matically regulated to compensate for changes in

cable loss resulting from temperature variations. The
12- to 99-ke band includes twelve telephone message
channels occupying the 12-ke to 60-ke range, a pilot
or controlling frequency of 68 ke, and tones used for
test purposes at 83, 91, and 99 ke. When a field tele-
phone set (EE-8) and a portable test set (TS-712)
are connected to the repeater, personnel may ring
the attended points of the system and converse over
a voice-frequency order-wire circuit. Voice fre-
quencies are not amplified in the unattended re-
peater, however.

A block diagram of the repeater is shown in Fig-
ure 2. Power from a constant-current 0.1 ampere de
supply is sent along the cable from an attended
point, and is delivered to the two amplifiers used for
the two directions of transmission. As indicated in
the diagram, the tube heater elements are wired in
series. Current from the power supply flows through
the heaters, and the resulting voltage drop is used
as plate voltage for the tubes. One power supply can
power as many as three repeaters. The power Loop.
ING switcH in the center of the diagram permits
connecting the de power path so that the current
either flows through the tube heaters and along the
next length of cable to the succeeding repeater, or,
if the repeater is the last of a series of three, “loops
back” and returns to the low side of the power sup-
ply. This arrangement requires good electrical in-

AN/TCC-11
peater on a pole, This repeater unit can also be
placed on the ground along the cable run.

sulation between the circuit “grounds” and the out-
side case, since the potential of the circuit “grounds”
relative to earth ground may be as high as 450 volts.

Of course, prime requisites for tactical military
equipment are that it be portable, rugged, and
reliable. This repeater is designed especially for an
exposed environment so that it may lie on the
ground or be strapped to a pole (see Figure 1) with-
out shelter, in either arctic or tropic climates. The
electrical apparatus is shock-mounted inside a
waterproof cylindrical aluminum case 28%” long and
10” in diameter, The complete assembly weighs only

83 Ibs. Removable covers over ports at each end
provide access to cable connectors and test points.
The power looping switch and a three-position
REPEATER SWITCH (discussed later) are also reached
through covered ports on the end sections. The ease
of installing and removing the repeater merely by
connecting the ends of the cable sections to the
mating conductors on the case simplifies the main-
tenance of the system.

It is beyond the scope of this article to describe
the component parts of the repeater in detail, but a
few facts and figures deserve mention. The gain of
the amplifiers at the pilot frequency (68 kc) is ap-
proximately 22.4 db at a temperature of 45°F, the
assumed average temperature. Equalization is built
into the amplifiers so that at average temperature,
the shape of the loss vs frequency characteristic of
5% miles of cable is compensated within + 0.06 db at
all frequencies in the message band. Regulation of
the gain characteristic of each amplifier is accom-
plished by means of an ambient temperature-sensi-
tive thermistor, which controls the loss characteristic
of a network associated with the amplifier. If the
thermistor temperature follows the cable tempera-
ture, compensation for the cable loss variations will
be obtained. This compensation is only approximate,
of course, since the temperature of the cable and the
temperature of the thermistor will seldom be iden-
tical. However, errors in the transmission character-
istic will accumulate to only a moderate amount
between attended points (2.4 db at 68 ke at the end
of a 6-repeater span for a 20°F difference in cable
and thermistor temperature at each repeater ). More-

FILTERS f TERS
LOW VOICE FREQUENCY ORDER w f LOW
PASS PASS |
al bo
ae |! ,
PASS DELAY BA PASS |
| REPEATER
SWITCH
TUBE HEATER ELEMENTS THERM
‘
ver | WER
' LOOP PING
TER
ER LOOPIN Fig. 2— Block
J
gram of AN/TCC-11
THERMIS
6 unattended repeater.
FILTERS | EQUALIZER! FILTERS
BA LAY HIGH
LOW
FREQUENCY ORDER WIRE PAT pace
>

over, at the attended points additional equalization,
both manual and automatic, is supplied to com-
pensate for the accumulated error.

Figure 4(a) shows the predicted transmission
characteristics of a 200-mile system under the condi-
tion that the repeater and cable temperatures are
equal at 45°F, and under the further conditions that
the repeater temperature is 20° above or below the
cable temperature. The closeness of the three curves
is an indication of the regulator performance, and
the rather modest departure from uniform gain over
the frequency band shows the extent to which the
system transmission is equalized. Figure 4(b) shows
the variation of the same 200-mile system character-
istic when the ambient temperature varies + 30°F

from an initial temperature of 125°. Equally good
performance is obtained when the initial tempera-
ture is —30°F.

An interesting and important feature of the
AN/TCC-11 repeaters is the built-in fault-locating
apparatus, Each repeater contains a tunable band-
pass filter ( called a “looping filter” in the right hand
part of Figure 2) bridged across the two directions
of transmission. This filter provides a tuned coupling
path between the two directions of transmission at
83 ke, 91 ke, or 99 ke. A three-position REPEATER
switcH selects the proper pass band, which depends
upon whether the repeater is the first, second, or
third from the attended point at which power is
supplied. If a repeater fails, the attendants at the
nearest attended point can apply the $3-, 91-, and

3
‘ CABLE 20°F
COLDER THAN
AMPLIFIERS >
=~ AMPLIFIERS CABLE 20°F
_— AND CABLE WARMER THAN
AT 45°F AMPLIFIERS
4
-2
VU
w-3
ra)
z 3
125° F + 30°F =155°F
> }
<
1
0
~ |
125°F —30°F = 95°F
~3
10 5S 20 25 30 35 40 45 50 55 60 65 70
FREQUENCY IN KILOCYCLES PER SECOND
Fig. 4 (a) Gain-frequency characteristics of 200-

mile system, showing changes when cable is colder
or warmer than amplifiers; (b) characteristics for

99-ke test tones to the line and measure the signal
returned in the opposite direction of transmission.
The faulty repeater will not return the applied tone.

Cable breaks in general produce power alarm
indications at attended points and can be located
by resistance measurements of the line. If power
fails, relays in the repeaters release and connect
100,000-ohm resistors across the line. If, then, a
break has occurred between the first and second
repeater, a resistance measurement will indicate a
resistance of about 100,000 ohms. If the break is
between the second and third repeater, the resist-
ance will be about 50,000 ohms, and so on.

At intervals up to 40 miles along the cable,
the attended AN/TCC-S5 repeater is inserted in the
transmission path, This repeater is shown in Figure
3, Like the AN/TCC-11, it amplifies, equalizes, and
regulates signals in the 12- to 68-ke range (a block-
ing filter stops incoming high-frequency test signals
before amplification ). In addition, this repeater in-
cludes voice-frequency order-wire amplification,
equalization, and signaling circuits; a test set is also
provided which enables measurements to be made
at various test points in the power and transmission
circuits. A 200-volt power supply delivers de power
to the attended equipment, and two 600-volt, 0.1-
ampere constant-current supplies deliver power over
the cable to as many as three unattended repeaters
in each direction of transmission.

CABLE CABLE
| “BUILDING "BUILDING
pass Out” WW OuT"
FILTER gh at DEVIATION
NETWORK LA) LSLOPE) (DELAY) (BULGE) | BASIC EQUALIZER NETWORK
i
SPIRAL-
FOUR
CABLE
REGULATING
aan PASS BUILDING AND = = = BUILDING
EQUALIZER ULGE} |DELAY| |sLopEe} | FLAT NETWORK

Figure 5 is a simplified diagram of the components
in the carrier frequency transmission path. Man-
ually adjustable equalizers permit accurate compen-
sation for manufacturing or other variations in the
cable and repeater characteristics, Equalizers with
the same loss characteristics as various lengths of
cable are provided so that short lengths of cable,
which may precede or follow the attended point in
a given direction of transmission, can be “built out”
to the nominal 5%-mile length. The regulating system
at the attended point operates under the control of
the 68-ke pilot transmitted from the terminal, The
68-ke pilot is picked off at the output of the at-
tended station amplifier through a narrow-band
filter, then amplified and rectified. The rectified
voltage is used to control the loss of the regulating
network by varying a thermistor element. The reg-
ulator network, like that in the unattended repeater,
has a loss-frequency characteristic that compensates
for the cable attenuation variations. This shape also
matches the transmission deviations not compen-
sated for by the unattended repeater. These devia-
tions are “mopped up” at the attended points. Reg-
ulators operate over a + 5-db input variation to
produce less than a + 0.5-db output variation.

Block diagram of the carrier frequency transmission paths of the AN/TCC-8 telephone repeater.

Again, the military requirements of portability,
reliability, and ruggedness were important con-
siderations from the standpoint of equipment de-
sign. The attended stations will always be provided
with some sort of shelter, so waterproof containers
are not essential. However, with the covers latched
in place, these containers are rainproof and are suit-
able without added protection for storage and trans-
portation over long distances in all climates. As
shown in the photograph (Figure 3), the complete
repeater consists of five boxes. The heaviest (the
one containing the repeater panel) weighs 118 Ibs.,
and the total weight of the complete repeater is 511
lbs. The boxes have specially notched edges so that
the individual units can be stacked as shown in the
figure. Inter-unit cables and cable connectors are
used to interconnect the various circuits quickly
and easily.

The Signal Corps has conducted trials of both
repeaters. They were subjected to severe vibration,
shock, “bounce,” heat, and humidity tests, and elec-
trical tests were made on the units in an experi-
mental cable system. These trials furnished data for
final adjustments in design so that, as produced, the
repeaters give excellent performance in all respects.

Joun M. Barstow, Jn. received his degree of B.S. in Electrical Engineering
from the University of Kentucky in 1949. He joined the technical staff of Bell
Telephone Laboratories in February of that year and enrolled in the Labora-
tories Communications Development Training Program. In 1950 he joined the
Transmissions Systems Development Department where he was engaged in the
development of military carrier systems and in the development of the trans-
atlantic submarine cable system. Prior to his resignation from the Laboratories
in January 1956, he was associated with military communication systems studies,

The Laboratories will institute a program of fel-
lowship awards to allow a few outstanding students
in the Communications Development Training Pro-
gram to acquire their Ph.D. degrees while continu-
ing as regular Laboratories employees. Awards will
normally be made at the end of the students’ first
year in C. D. T. A small number will be made
each year, depending upon the size of the C. D. T.
class and the merit of the candidates. This year one
or two additional awards will be made to candi-
dates who completed their first year in C. D. T.
prior to this year. First selections will be made
later this year.

Nominations for fellowships will be made by the
Department of Education and Training, and awards
will be made by the C. D. T. Policy Committee,
consisting of E. I. Green, Chairman, H. W. Bode,
R. R. Hough, A. D. Knowlton, F. D. Leamer, M. B.
McDavitt, and S. B. Ingram, Secretary.

Fellows will be selected from the upper scholastic
level of C. D. T. with consideration being given
to performance on rotational assignments, poten-
tial as Laboratories employees, and promise of bene-
fit from advanced academic training. The fellow-
ship program is expected to strengthen the
Laboratories staff by the further academic devel-
opment of outstanding Communications Develop-
ment Training students.

Choice of institution will be made jointly by the
fellow and the C. D. T. Policy Committee, with
proximity to the Laboratories being one considera-
tion. Fellows will continue as Laboratories em-
ployees, drawing full salary and receiving regular
employee benefits. Allowances will be made for
tuition, books, and certain other expenses, During
academic vacations, Fellows will return to the
Laboratories where they will work on projects in
various technical departments.

A wind tunnel, normally employed in aerody-
namic studies, was recently used by the Labora-
tories to simulate the effect of hurricane conditions
on some telephone apparatus. Acting on a request
by the A.T.&T. Co., members of the Outside Plant
Development and General Staff Departments at the
Point Breeze Laboratory conducted a series of tests
to determine what effect hurricane winds would
have on a “Ready-Access” cable terminal. This
terminal is a device used to provide entrance from

D. Gross, Director of the Univ. of Maryland wind tunnel,
center, with P. P. Kaliss, left, and W. J. Fullerton of BTL
in the test room of the Univ. of Maryland wind tunnel.

To perform these tests, arrangements were made
with the University of Maryland to use the wind
tunnel on their campus at College Park, Maryland.
Cable terminals were set up in this wind tunnel
and subjected to various wind velocities up to and
including 200 miles per hour. The terminals sur
vived the tests without damage.

“Ready-Access” cable terminal after it was sub-
jected to 200-mile-per-hour winds.

Cleo F. Craig, President of the A.T.&T, Company,
greeted share owners at the 1956 Annual Meeting.

Bell Companies will spend more than $2 billion
for new construction this year, Cleo F. Craig, presi-
dent of the American Telephone and Telegraph
Company, told share owners at the company’s 7st
annual meeting in New York City, Such an amount
for growth and improvement in any one year is the
largest on record for the System. It is also the
largest ever planned for a single year’s expendi-
ture by any American business.

“So far this year new orders are considerably
ahead of 1955,” Mr. Craig reported to the share
owners. Barring unforeseen developments, the Bell
System should be celebrating 50 million telephones
in service when the share owners meet in 1957.
This compares with about 47 million today,

“Long distance business also continues to show a
good healthy growth,” Mr. Craig said. This is only
partly due to the increase in telephones, although
that is an important factor, We increase long dis-
tance usage by going out and selling it, Mr. Craig
pointed out, and we also promote service by making
it more attractive and convenient to use. Mr.
Craig cited direct distance dialing as a powerful
incentive for our customers to use long distance.
All this growth and improvement is the reason for
the slightly more than $2 billion in new construc-
tion by the Bell System companies in 1956.

“For most of their new equipment,” Mr. Craig
said, “the companies rely on Western Electric, the
manufacturing and supply organization of the Sys-

tem.” “Last year,” as the Annual Report pointed out,
“Western Electric did a remarkable job of increas-
ing production. This year they are turning out even
more cable, dial equipment and various types of
telephone instruments.”

The share owners met in a new location — the
sixth floor at 50 Varick Street in downtown New
York. A.T.&T. purchased the building in 1953 to
provide more room for sections of the Treasury
and the Comptroller's departments, Earlier this
year the Company completed a three-floor addition,
and space on the sixth floor can be used from time
to time for meetings of this kind.

In answer to questions from the floor concerning
the 1955 Annual Report, Mr. Craig replied that
last year’s advertising expense was less than one
per cent of operating expenses; that the recent anti-
trust suit consent decree would not disturb the
relationship among Bell Telephone Laboratories,
Western Electric and the Associated Bell Com-
panies; and that profits from work done for the
Department of Defense average about four per cent.

Share owners re-elected each of the 19 incum-
bent A.T.&T. directors, with votes in excess of
41,000,000. They also re-elected the firm of Lybrand,

Fred R. Kappel, President of the Western Electric
Company, introduced a motion picture about
Western Electric at the: stockholders meeting.

Ross Brothers & Montgomery, auditors. During the
discussion following nominations for directors, Mr.
Craig announced that last year the directors them-
selves had decided to establish a retirement age
of 72, to be fully effective by 1960. While ballots
for directors and auditors were being counted,
Fred R. Kappel, president of the Western Electric
Company, introduced a color film which dramatic-
ally told of the important role played by Western
Electric in serving both the Bell System and na-
tional defense.

During the meeting, more than a score of the
share owners present used the microphones pro-
vided to ask questions or make comments. In the
general discussion period at the end of the meeting,
attention centered on earnings and dividends, and
of whether the stock should be split.

Mr. Craig stated the present position of the Board.
He said in part: “We have made very careful studies
to find out what happens to companies when they
split their stock. Where there is an announcement
of a stock split, the price of stock goes up. There
is a flurry in the stock market and a rise in the
price of the stock.

“But if there is no substantial dividend increase
at the time of the stock split, or shortly thereafter,
that stock goes down in the market. In almost
every case it goes down below where it was before.
There is a spurt, and then a feeling of quite acute
disappointment. The stock winds up in a poorer
place, financially, after the split than before the split,
if the trend of the market is taken into account.

“If the telephone company were to split without a
dividend increase,” Mr. Craig continued, “the price
of the stock would go up on the market tempo-
rarily. That would benefit some people who bought
the stock on a short-term basis. It would not bene-
fit the people who want to keep the stock as a per-
manent investment,” Mr, Craig stated. “A stock split
without any increase in dividends to share owners
would be a very short-sighted and damaging step
for the company to take. Unless there is a divi-
dend increase at the same time there is a stock split,
the speculators may be able to make a profit on the
rise and fall in the market. The Board of Directors
is not going to take action with respect to the stock
merely to push the price up and down on the
market.”

In discussing the question of a dividend increase,
Mr. Craig pointed out that American Telephone and
Telegraph stock bought on the market today brings
a 4.9 per cent return on the money invested. The
company, however, has been able to put only a lim-

ited amount per share into undistributed earnings.
Six years ago there were 25 million shares out-
standing and today there are 55 million shares out-
standing. On the average, about five million shares
have been added each year. In 1949 there was
$14.23 in undistributed earnings per share
a year and a half's dividend protection, There has
to be a certain amount of undistributed
to protect the whole financial situation.
The company has expanded by nearly 30 million
shares. In that period undistributed earnings per
share have risen from $14.23 to $19.99. This means
not only that nearly $6 per share has been added
to undistributed earnings, it means the business has
earned enough to put into surplus for each new
share an amount equivalent to the surplus per share
that existed before those new shares were issued.
Mr. Craig pointed out that in 1955
started with $18.19 in undistributed
share.

the company
earnings per
Roughly, six million shares were added. So
for each of the six million shares, the company had
to earn, in addition to the dividend payable on
those shares, $15.19 for surplus in order to protect
all the previous shares outstanding. What was left
after that could be added to the surplus per share,
and $1.80 per share was added last year.

Last year the company, for the first time in a
long time, paid out only 69 per cent of earnings in
dividends. The Board of Directors is trying to take
whatever is left over and put it back into the busi-
ness, and make that earn for the share owners.

Dr. Mervin J. Kelly declared to engineering edu-
cators last month that our nation is engaged in a
technological race for strength, and urged that we
. move ahead as fast as we can.

Speaking at a conference of more than 300 mem-
bers of the American Society for Engineering Edu-
cation, Dr, Kelly described the nation’s expanding
need for scientists and engineers and emphasized
the need for more and better training of both re-
: search and development people. He also suggested
‘ that educators consider establishing a fifth year for
the basic engineering course and then recommend
it to all planning a career in research and develop-
ment so that these students would receive more
engineering fundamentals. He also urged that many
more students continue their training to the doc-
torate level. The conference was the Spring Meet- for a Career in Industry.” Dr. Kelly's keynote ad-
ing of the A.S.E.E. Middle Atlantic Section, held dress was entitled “Preparation for a Career in De-
May 12 at Bell Telephone Laboratories, Murray velopment and Research.”

Hill, N. J. In stressing the need for more and better engi-
: Concerned with the critical shortage of engineer- neering training, Dr. Kelly pointed out that the four-
Ae ing graduates, the all-day conference had as its year engineering graduate generally lacks sufficient
theme the “Preparation of Engineering Students training. He showed how Bell Laboratories’ belief
in more education is exemplified in the Communi-
cations Development Training program, established
in 1948 as a three-year course for newly employed
engineers with bachelor’s and master’s degrees.

In suggesting a five-year engineering course, Dr.
Kelly explained that it could be arranged so that
students could stop at the end of four years or con-
tinue for the fifth year. This fifth year would be
advisable, he said, regardless of whether the stu-
dent went on for a doctor's degree. Dr. Kelly also
urged industry to place greater emphasis on basic
research and recommended that research activities
be separated from development and design activities.

Dr. Kelly described the successful experiment of
Bell Laboratories which 20 years ago separated re-
search from the development and design functions
within the company. He explained that the Labora-
tories worked to create an environment of freedom
comparable to that found on university campuses —
Members of the American Society for Engineering Educa- freedom in research, freedom to publish, and free-
tion attended morning meeting in the Arnold Auditorium dom to intermingle with scientific people through-
at the Murray Hill laboratory. out the world. “The results of the work done in this

Dr. M. J. Kelly addresses the spring meeting of
Middle-Atlantic Section of the American Society
for Engineering Education at Murray Hill.

area of basic research have created a reservoir of
knowledge which, for a long time, will contribute
to improvements in communications,” he said, Dr.
Kelly also insisted in his address that the research
scientists must have “the freedom to wander into
the area of tomorrow.”

In urging that the nation move ahead technolog-
ically as fast as it can, Dr. Kelly told of experiences
related to him by a professor of aGerman Technische
Hochschule. The professor had been forced to
work in Russia, and his evidence indicated that top
Russian engineering students are more advanced
than their counterparts in America.

Dr. Kelly was introduced by R. Karl Honaman,
Director of Publication. In welcoming members of
the society to Murray Hill, Mr. Honaman expressed
the belief that “the community of interest between
industry and education is stronger in the field of
engineering than in any other area of professionals
and their educators. Through common member-
ships in professional societies and as individuals in
contact with each other in both groups, this com-
munity of interest is strengthened.”

Important problems in the field of engineering
education were discussed at three afternoon meet-
ings, as follows: “Preparation of Engineering Grad-
uates for Industry” — Chairman; Sydney B. Ingram,
Director of Education and Training at Bell Labora-
tories. Speakers: Morris D. Hooven, Public Service
Electric & Gas Company and President of the
A.I.E.E.; Henry N. Meixner, General Assistant Di-

rector, Mechanical Development Laboratory, E. 1.
du Pont de Nemours & Company, Inc.; and Frank
W. Miller, Vice President — Manufacturing, Yarn-
all-Waring Company, Philadelphia.

“Preparation of Secondary School Graduates for
Engineering” — Chairman; Elmer C. Easton, Dean
of Engineering, Rutgers University. Speakers; Lynn
L.. Merrill, Dean of the Faculty, Stevens Institute of
Technology; Harold K. Work, Director of the Re-
search Division, College of Engineering, New York
University; and Ablett H. Flury, Assistant Commis-
sioner of Education for the State of New Jersey,
who delivered a paper by Frederick Raubinger,
Commissioner of Education.

“Current Engineering Manpower Needs in Indus-
try and the Colleges” — Chairman: Donald S. Bridg-
man, Director of College Relations, American Tele-
phone and Telegraph Company. Speakers: William
T. Cavanaugh, Executive Secretary, Engineering
Manpower Commission of the Engineers Joint Coun-
cil; and Robert W. van Houten, President, Newark
College of Engineering.

Projects, Western Electric Company, gave a re-
cently declassified account of construction of the
Distant Early Warning Line which guards our Are-
tic continental approaches,

Arrangements for the conference were made by a
Laboratories committee headed by Frank D. Lea-
mer, Personnel Director.

Dr. M. J. Kelly was elected a director of The
Economic Club of New York at a meeting in New
York City April 16. His term of office is for three
years beginning June 1, 1956,

The Economic Club is an association whose ob-
jectives are: “to contribute toward building a
stronger business leadership in America; to provide
a platform for discussing those problems that af-
fect the business community, and to develop an
informed opinion among all citizens as to the aims
and achievements of our economic system.”

Dr. Kelly also recently accepted a post on the
New York City Board of Education's Advisory
Committee on Science Manpower. In this capacity,
he is chairman of a subcommittee on the Role of
Industry and Colleges.

The first field trial of a rural telephone system
making use of transistors and the Bell Solar Bat-
tery, held in Americus, Georgia, has been con-
cluded with satisfactory results. The Bell Solar
Battery was installed on a part of this trial system
in October, 1955, as an experimental substitute for
ordinary batteries, the conventional source of elec-
trical power for such a system where power lines
are not readily available. Power engineers report
that the Bell Solar Battery, first device to change
sunlight directly and efficiently into useful amounts
of electricity, has lived up to expectations.

Bell System engineers have ascertained from the
Georgia tests that, from the standpoint of reli-
ability and effective operation, the Bell Solar Bat-
tery mounted on a pole can be used to furnish elec-
tricity for rural telephone equipment. The favorable
operation report on the Solar Battery, however, does
not mean that regular commercial use of the device
is as yet practical. Until the ultra-pure silicon used
in the device becomes less expensive, it will be
more economical to use conventional power sources
for telephone systems. Hence, no further trials of the
Bell Solar Battery are planned immediately.

Of more significance for telephone customers
and electronics engineers is the future indicated
for the transistor, The Georgia tests have justified
the confidence placed in the transistor as a key to the
planning of future telephone systems.

About 275 transistors were used in the Americus
trial. The short-haul, rural telephone system that

was tried out derives its economy largely from the
use of transistors instead of electron tubes which
should help make it possible to provide improved
telephone service in thinly populated rural areas.

Another device, used for the first time in the
experimental system, made transistor use practical.
This is a lightning protector which affords the low-
power transistor special protection against elec-
trical surges. This new device — called a “silicon
aluminum junction diode” —in conjunction with
standard protectors will protect transistors from
ordinary lightning damage. This lightning pro-
tector evolved from the same basic research as the
transistor itself and belongs to the same general
family of semiconductor devices.

San Diego First Large City Added to
Nationwide Customer Dialing Network

The recent cutover of the University Crossbar
Tandem Office in San Diego, California, marked
another major step along the road toward nation-
wide direct distance dialing. This was the first oc-
casion in which an entire large multi-office city,
served by the Bell System, was arranged for direct
distance dialing. (In 1950, San Diego had a popula-
tion of about 435,000, and in 1953, it had about
130,000 telephone customers. )

The San Diego cutover also marked the first oc-
casion in which a city served by step-by-step cen-
tral offices was included in the nationwide dialing

The May, 1956, issue of The Bell System
Technical Journal contains the following:

Chemical Interactions Among Defects in
Germanium and Silicon by H. Reiss, C. S.
Fuller and F. J. Morin.

Single Crystals of Exceptional Perfection |
and Uniformity by Zone Leveling by D.C. |
Bennett and B. Sawyer.

A Laboratory Model Magnetic Drum Trans-
lator for Toll Switching Offices by F. J.
_ Buhrendorf, H. A. Henning and O. J. Murphy.
Tables of Phase of a Semi-Infinite Unit At-
| tenuation Slope by D. E. Thomas.

plan. This was made possible by new centralized
automatic message accounting and toll features in
the crossbar tandem switching system which will
ultimately provide service for 10,000,000 customers
in about 100 step-by-step cities.

The University Tandem office serves 31 local
central offices in the San Diego area, It is a pri-
mary outlet in the nationwide dialing plan.

The Laboratories, at the request of the National
Academy of Sciences, presented a number of dem-
onstrations at the annual meeting of the Academy
held in Washington, D. C., recently. Among these
were demonstrations that showed the applications
of new ferroelectric memory devices.

One of these was a ferroelectric shift register—
a device in which stored binary digits can be simul-
taneously moved from one cell to another without
interfering with each other. This apparatus can
perform a number of basic operations that make
it useful for data processing applications, such as
digital computing and automatic switching. These
include; data storage; pulse counting; the ability
to transfer information between devices with widely
different pulse rates; and the ability to accept pulses
one-at-a-time, store them until the sequence is com-
pleted, and then transfer them all-at-once.

To permit definite planning to meet the Labora-
tories’ needs for more working space, the Board of
Directors has authorized the preparation of plans
and specifications for major building facilities to
be constructed on the Laboratories’ property at
Holmdel, New Jersey.

Presently authorized construction, including the
proposed office building and the single-story ware-
house-type building at Murray Hill and additional
space at Western Electric locations, are expected to
provide for space needs through 1958, The Labora-
tories is now authorized to prepare detailed plans
and specifications for a building unit at Hoimdel
to be started within the next year to provide for
Laboratories space needs for a reasonable period
beyond 1958, It is expected that this first unit
would provide space for about 1,500 people. Also
authorized is the preparation of an over-all building
layout for Holmdel so that if future Laboratories
space needs justify it Holmdel could be built up

J. Reid Anderson, of the Laboratories Switching Research
Department, demonstrates a ferroelectric shift register at
the annual meeting of the National Academy of Sciences.

under an orderly and efficient plan to become a
major location about the size of Murray Hill.

Preliminary studies indicate that Holmdel is a
highly desirable location for Laboratories purposes.
This location is near enough New York, Murray
Hill and Whippany for necessary inter-location
travel, yet sufficiently separated to avoid overcon-
centration in any one area. It is believed undesir-
able to expand sizably beyond present plans at
either Murray Hill or Whippany. Similarly, there
appears to be good reason for not enlarging the
New York location. Transportation, concentration,
availability of suitable manpower, recruiting of pro-
fessional people, accessibility of residential areas,
and many other factors have been we ighed in the
decision to enlarge at Holmdel.

Holmdel, where there are now about 130 Labora-
tories employees, is about 25 miles from Murray
Hill and about 45 minutes in time by automobile
on the Garden State Parkway. It is only a little
farther from Whippany and about an hour from
New York. There is also rail and bus transportation
from New York. The Laboratories now owns about
450 acres at this site.

The authorization given by the Board of Di
rectors includes funds for: surveying, engineer-
ing and architectural services necessary to plan the
long-term, over-all program; engineering and archi-
tectural services to produce complete drawings
and specifications for the first building unit; and
drilling of wells at Holmdel required to prove the
adequacy of the water supply to meet the needs of
the program. It is expected that the planning can
be completed in time to start construction of the
first step in the project late in 1957 or early 1955.

Patents Issued to Members of Bell Telephone
Laboratories During March

Brooks, C, E., McGuigan, J. H., and Murphy, O. J. — Mag-
netic Drum Dial Pulse Recording and Storage Registers
2,738,382.

Fox, A. G. — Wave-guide Impedance Elements
Grisdale, R. O., and Sauer, H. A.
Conducting Coils — 2,739,371.
Holden, W. H. T. — Station Number Identifier
Houtz, C. C., and McLean, D. A.
trolytic Capacitors — 2,739,275,
Hunt, L. F., and Schafer, 5. P. Method and Apparatus
for Detecting and Correcting Amplitude Distortion

Newby, N. D. — Magnetic Scanning Arrangement Providing
Compensation for Battery Variation and Variation of
Other Components — 2,739,183.

Newby, N. D. — Rotational Use of Register Circuits in Tele-
phone Switching Systems — 2,740,003.

Wallace, R. L., Jr. — Transistor Amplifiers and Circuit Ar-
rangements Therefor — 2,739,190.

Following is a list of the authors, titles, and place of publication
of recent papers published by members of the Laboratories.

Ahearn, A. J., and Law, J. T., Russell Effect in Silicon and
Germanium, |, Chem, Phys., Letter to the Editor, 24,

Bashkow, T. R., DC Graphical Analysis of Junction Tran-
sistor Flip-Flops, Comm, and Elec., 23, pp. 1-6, Mar.,
1956,

Bennett, W. R., Synthesis of Active Networks, Proc, Symp,
Modern Network Synthesis, MRI Symposia Series, 5,
pp. 45-61, 1956,

Bennett, W. R., Electrical Noise. Il — Noise Generating
Equipment, Electronics, 29, pp. 134-137, Apr., 1956.
Bommel, H. E., Mason, W. P., and Wainer, A. W., Dislo-
cations, Relaxations and Anelasticity of Crystal Quartz,

Bozorth, RK. M., Quelques Propriétés Magnétiques, Elec-
trioques Et Optiques Des Films Obtenus Par Electrolyse
Et Par Evaporation Thermique, Le |. De Physique Et
Le Radium, 17, pp. 256-262, Mar., 1956.

Clogston, A. M., Suhl, H., Walker, L. R., and Anderson,
?. W., Possible Source of Line Width in Ferromagnetic
Resonance, Phys. Rev,, Letter to the Editor, 101, pp.
903-905, Jan. 15, 1956.

De Leeuw, K., Moore, E. F., Shannon, C, E., and Shapiro,
N., Computability by Probabilistic Machines, Automata
Studies, Princeton Univ. Press, pp. 183-212, Apr. 1956,

Haynes, J. R., and Westphal, W. C., Radiation Resulting
from Recombination of Holes and Electrons in Silicon,
Phys. Rev., 101, pp. 1676-1678, Mar. 15, 1956.

Law, J. T., and Francois, E. E., Adsorption of Gases on
Silicon Surface, J. Chem. Phys., 60, pp. 353-358, Mar.,
1956,

Lloyd, S. P., and McMillan, B., Linear Least Squares Fil-
tering and Prediction of Sampled Signals, Proc. Symp.,
P.1.B., 5, pp. 221-247, Apr. 1955.

Moore, E. F., Gedanken-Experiments on Sequential Ma-
chines, Automata Studies, Princeton Univ.
129-153, Apr., 1956.

Remeika, J. P., and Merz, W. ]., Guanidine Vanadium
Sulfate Hexahydrate: A New Ferroelectric Material, Phys.
Rev., Letter to the Editor, 102, p. 295, Apr. 1, 1956,

Sullivan, M. V., and Eigler, J. H., Five Metal Hydrides
as Alloying Agents on Silicon, |. Electrochem, Soc., 103,
pp. 218-220, Apr., 1956.

Turner, D. R., The Anode Behavior of Germanium in Aque-
ous Solutions, |. Electrochem. Soc., 103, pp. 252-256,
Apr., 1956.

Uhlir, A., Jr., High-Frequency Shot Noise in PN Junctions,
Proc, LR.E., Correspondence, 44, pp. 557-558, Apr., 1956.

Van Haste, W., Statistical Techniques for a Transmission
System, Comm. and Elec., 23, pp. 50-54, Mar., 1956,

Van Haste, W., Component Reliability in a Transmission
System, Elec. Engg., 75, p. 413, May, 1956.

Van Roosbroeck, W., Theory of the Photomagnetoelectric
Effect in Semiconductors, Phys. Rev., 101, pp. 1713-1724,
Mar. 15, 1956.

Wahl, A. J., and Kleimack, |. J., Factors Affecting Relia-
bility of Alloy Junction Transistors, Proc. LR.E., 44, pp.
194-502, Apr., 1956,

Weisbaum, C., and Boyet, H., A Double-Slab Ferrite Field
Displacement Isolator at 11 KMC, Proc, LBRLE., 44, pp.
554-555, Apr., 1956.

During April, a number of Laboratories people gave talks before professional and
educational groups. Following is a list of speakers, titles, and places of presentation.

Biondi, F. J., Status of Semiconductor Technology.
Guldner, W. G., see Thurmond, C. D.

Haynes, J. R., Radiation Resulting from the Recombination
of Holes and Electrons in Silicon.

Law, J. T., The High Temperature Oxidation of Germanium,
Smith, K. D., see Veloric, H. S.

Thurmond, C. D., The Distribution of Copper Between Ger-
manium and Ternary Melts Saturated with Germanium,
Thurmond, C. D, Guldner, W. G., and Beach, A. L., Mydro-
gen and Oxygen in Single Crystal Germanium as Deter

Anderson, J. R., Ferroelectric Devices and Some Circuit Ap-
plications, R.C.A. Research Laboratories, Princeton, N. J.

Anderson, O. L., The Structure of Inorganic Glass in View
of Recent Measurements on Volume Flow, Brooklyn Poly-
technic Institute, Chemistry Symposium, New York City.

Anderson, P. W., and Suhl, H., Nonlinearities in Ferromag-
netic Resonance at High Power, Armour Research Founda-
tion, Relaxation Phenomena in Ferromagnetic Materials
Symposium, Chicago, Il.

Baker, W. O., Materials for Future Electronics, New Eng-
land Radio-Electronics Meeting, Boston, Mass.

Bangert, J. T., The Transistor as a Network Element,
A.LE.E. — LR.E., Lehigh University, Bethlehem, Pa.

Biggs, B. S., Effect of Air Pollution on Elastomeric Products
in the Telephone Plant, Detroit Rubber and Plastics Group,
Detroit, Mich.

Budlong, A. H., Mechanized Intelligence, Montclair Society
of Engineers, Upper Montclair, N. J.

Cioffi, P. P., Rectilinearity of Electron Beam Focusing Fields
from Transverse Component Determinations, A.LE.E.,
Great Lakes District Meeting, Fort Wayne, Ind.

Clogston, A. M., Disorder Scattering of Spin Waves, Armour
Research Foundation, Relaxation Phenomena in Ferromag-
netic Materials Symposium, Chicago, IIL.

Dillon, J. F., Jr., Motion of Single Domain Walls in Man-
ganese Ferrite, American Physical Society, Washington.

Fay, C. E., Ferrite-Tuned Resonant Cavities, Microwave
Properties and Applications of Ferrites Symposium, Har-
vard University, Cambridge, Mass.

Ferrell, E. B., The Control Chart — Modifications and Ex
tensions, American Society for Quality Control, Montreal
Section, Canada.

Finch, T. R., Science and Tomorrow's Communications, lowa
State Science Fair, Cedar Falls, lowa.

Foster, F. G., Preparation Methods for Materials Microscopy,
Metropolitan Microchemical Soc iety, American Museum
of Natural History, New York City.

Frost, G. R., Logic of Switching Circuits, Queens College,
Physics Club, Flushing, N. Y.; and Columbia University,
New York City,

Fthenakis, E., A Voltage Regulator Using High Speed of
Response Magnetic Amplifiers with Transistor Driver,
A.LE.E LR.E.—LS.A., Special Technical Conference
on Magnetic Amplifiers, Syracuse, N. Y.

Galt, J. K., Ferromagnetic Domain Wall Motion, Physics
Colloquium, New York University, New York City.

Geballe, T. H., Thermomagnetic Effects in Germanium, Uni-
versity of Pennsylvania, Philadelphia.

Gilleo, M. A., Magnetism in the Perowskite Structure System,
Solid State Physics Seminar, Physics Department, Uni
versity of Pennsylvania, Philadelphia.

Goldstein, H. L., and Lowell, RK. J., Magnetic Amplifier Con-
trolled Regulated Rectifiers, AA.E.E. — LBB. — LS.A,,
Special Technical Conference on Magnetic Amplifiers,
Syracuse, N. Y.

Gordon, J. P., The Maser, LR.E. Long Island Section, Garden
City, L. L; and Union of Radio Scientific Internationale
Convention, Washington, D. C

Hagelbarger, D. W., SEER—A Sequence Extrapolating
Robot, Seminar on Digital Computers, Joint Student
Branch, A.LE.E, — LBLE., Polytechnic Institute of Brook
lyn, New York City; and A.LE.E. — LBLE., Joint Student

Hamming, R. W., and Rhodes, Mrs. Ida, General Use of
Digital Computers, General Services Administration Audi-
torium, Washington, D. C.

Hardy, F., Lubricants and How to Use Them, A.LE.E. New
York Section, New Jersey Division, Newark,

Haynes, J. K., Radiation Resulting from the Recombination
of Holes and Electrons in Silicon, Massachusetts Institute
of Technology, Physics Department Colloquium, Cam-
bridge, Mass.

B Sample; Picking the Best of K Binomial Processes; and
Comparison of Two Univariate Distributions, Army Chem-
ical Center, Edgewood, Md.

Kock, W. E., Undergraduate Honors — Precursors to Suc-
cess, 50th Anniversary Celebration of Cooperative Engi-
neering, Honorary Fraternities, University of Cincinnati,
Ohio; and Polarized Sound Waves, Physics Colloquium,
Brown University, Providence, R. 1.

Kudlich, R. A., TRADIC — A Transistor Digital Computer,
LR.E., Akron Chapter, Ohio.

Landgren, C. R., Transistors — Their Development and Ap-
plications, John Ericsson Society, Engineer's Club, New
York City,

Lewis, W. D., and Vaughan, H. E., Electronic Switching and
€ Data Transmission, American Management Association,
Integrated Data Processing Seminar, New York City.

phone Company, New York City.
Logie, J. R., Jr, NIKE 1 — A Guided Missile System for AA
Defense, —1.R.E., Student Activities Day, East-
erm District Papers Competition, Rutgers University, New
Brunswick, N.J.

Long, T. R., The Elastic Constants of Magnesium and Mag-
nesium Alloys, National Bureau of Standards, American
Physical Society Meeting, Washington, D.C.

Mattson, R. H., Properties of Junction Transistors, IRE,
Boston Section, Mass.

McDonald, H. S., Signal Theory Applied to Speech Proces-
sing, Johns Hopkins University, Electrical Engineering
Seminar, Baltimore, Md.

McKay, K. G., The Interaction Between Research and De-
velopment at Bell Telephone Laboratories, A.AE.E.
Pittsburgh Section, Pa,

Mealy, G. H., Deterministic and Probabilistic Prediction
Their Relation to the Theory of Automata, Columbia Uni-
versity, Discrete Sequence Transducers Seminar, New
York City,

Monro, S., Design of Experiments, Lehigh University, Grad-
uate Seminar, Bethlehem, Pa.

Morgan, S. P., Control of Spurious Modes in Multimode
Waveguides by Use of Foam Dielectric Inserts, Union of
Radio Scientific Internationale Meeting, Washington, D.C.

Paul, C. E., NIKE I — A Guided Missile for AA Defense, Sea
Explorer Scouts, Ship 20, Livingston, N. J.

Read, W. T., Jr., Dislocation Theory, Maryland Institute of
Metals, Baltimore; and Solid State, Conference on New
Developments in Engineering, University of Pennsylvania,
Philadelphia,

Reiss, H., Chemical Interactions Among Defects in German-
ium and Silicon, General Electric Company, Knolls Labora-
tory, Schenectady, N.Y.

Riesz, R. P., Mr. Meticulous, A.L.E.E. New York Section,
Communications Divisions, New York City.

Rowe, H. E., and Manley, J. M., General Energy Relations in
Non-Linear Inductors and Capacitors, Non-Linear Circuit
Analysis Symposium, Brooklyn Polytechnic Institute, New
York City,

Schroeder, M. R., Information Theory and Speech, Siemens
und Halske Zentrallaboratorium, Munich, Germany.

Seidel, H., Anomalous Propagation in Ferrite-Loaded Wave-
guide, Ferrite Symposium, Harvard University, Cambridge,
Mass.

Sharp, W. O., Submarine Cable Tube, Royal Arch Masons,
Corinthian Chapter, Westfield, N. J.

Shive, J. N., The Bell Solar Battery, Council of Agricultural
and Chemurgic Research, Chicago, Il; and Transistors
and Solar Batteries, New York Telephone Company, New
York City.

Sparks, M., Chemistry in Modern Communications, Waynes-
boro, Sweet Briar, Va; Greensboro, Wake Forest, Kinston,
Charlotte, N. C.; Ashville, Columbia, 8. C.; and Tallahas-
see, Lakeland, Gainesville, Fla.

Suhl, H., Non-Linear Behavior of Ferrites Under High Peak
Powers, Microwave Properties and Applications of Ferrites
Symposium, Harvard University, Cambridge, Mass.; and
Spin-Wave Effects in Ferromagnetic Resonance, Physics
Colloquium, Columbia University, New York City.

Tukey, J. W., Mathematics, Statistics and Computers, Amer-
ican Statistical Society, Pennsylvania State Chapter, Penn-
sylvania State University; and Society for Industrial and
Applied Mathematics, Central Pennsylvania Section.

VanUitert, L. G., The Dielectric Properties of and Conduc-
tivity in Ferrites, Microwave Properties and Applications
of Ferrites Symposium, Harvard University, Cambridge,
Mass.

Waltz, M. C., The Time Behavior of Transistors in Useful
Circuits, A.1.E.E., Winston-Salem, N. C.

Warner, R. M., Jr., Survey of Transistors for High Frequency
Use, LR.E. Pittsburgh Section, Mellon Institute, Pa.

Wilkinson, R. L, Some Queueing Theory for Engineers,
American Society for Quality Control, Metropolitan Sec-
tion, N. Y. C.

Winslow, F. H., Electrons in Organic Insulators, American
Chemical Society, Philadelphia Section, University of
Pennsylvania.

Young, J. A., and Morgan, S. P., Helix Waveguide, Union of
Radio Scientific Internationale Meeting, Washington, D. C.

New radio relay systems for telephone and
television now in the making will employ an
ingenious device invented by Bell scientists.
The device, known as an “isolator,” senses
which way microwaves are traveling in a wave-
guide, and stops those going the wrong way.

In the new systems a klystron wave gen-
erator sends signals through a waveguide to
the antenna. The klystron must be shielded
from waves reflected back along the wave-
guide by the antenna. The isolator stops re-
flections, yet allows the transmitted signals to
go through clear and strong.

This isolator is a slab of ferrite which is
mounted inside the waveguide, and is kept
magnetized by a permanent magnet strapped
to the outside. The magnetized ferrite pushes
aside outgoing waves, while unwanted re-
flected waves are drawn into the ferrite and
dissipated. This “field displacement” action
results from the interplay between micro-
waves and a ferrite’s spinning electrons.

This is another example of how Bell Tele-
phone Laboratories research works to im-
prove American telephony and telecommuni-
cations throughout the world.

Dr. S. Weishaum assembles an isolator which he
developed for use in a new microwave system. Dr.
Weisbaum is a Ph.D. in microwave spectroscopy
from New York University. He is one of many
young men at Bell Telephone Laboratories ap-
plying the insight of the physicist to develop
new systems of communication.

the isolator is a
ferrite slab.
Geometric pattern
is a carbon layer
which dissipates
reflected signals.

4 At a radio relay
station an isolator
assures one-way
transmission
from the output
of the amplifier
to the antenna.

Bell Laboratories Record  1956-06: Vol 34 Iss 6