PAGE
THE NEW LOOK IN TELEPHONE INSTRUMENTS
A MICROWAVE TRIODE FOR RADIO RELAY, J. A. Morton . . . 166
COVER SHEET FOR TECHNICAL MEMORANDA
MOBILE RADIO ANTENNAS FOR RAILROADS, W.C. Babcock. . 172
ELECTRONIC TIMING TEST SET, M.E. Krom. . . . . . 176
TELEVISION I-F COIL DESIGN, J. H. Felker . . . . . . 18)

A new telephone instrument with better
hearing and speaking qualities, an im-
proved dial and a volume control for its
ringer is in final stages of development
at Bell Telephone Laboratories. Incorporat-
ing new scientific principles, new technical
art in applying them and new materials,
pre-production models are still undergoing
tests. It is expected that several thousands
of the new sets will be manufactured this
year and installed on a trial basis.

While nearly all of the more than 400
separate parts making up the set are of en-
tirely new design, the new telephone will
be completely interchangeable with tele-
phones now in use and when the new set
is connected with one of the current design,
users of both telephones will benefit.

Major objectives in designing the new
telephone were to provide, as economically
as possible, better all-round service. An
important feature is a novel “equalizer”
which automatically adjusts the sound-level
to compensate in part for the distance be-
tween the telephone and the central office.
The dial on the new set has the numbers
and letter prefixes outside the finger wheel
and is sloped at a lower angle, affording
better visibility.

to suit his needs. At its loudest, the tone
carries further than the present one; when
muted, it is softer.

Weight of the new telephone’s handset—
the transmitter and the receiver and the
handle on which they are mounted—has
been reduced 25 per cent. Slightly smaller
than earlier models, it is designed to pro-
vide a better fit to the head. All parts save
those in the handset are mounted on the
base, with the housing serving only as a
cover. This arrangement of parts on the
base is expected to facilitate manufacture,
installation and maintenance.

In developing microwave relay systems
for frequencies around 4,000 megacycles,
one of the major problems is to provide an
amplifier tube that will meet the require-
ments on gain, power output, and distortion
over very wide bands. As the number of
repeaters is increased to extend the relay to
greater distances, the requirements on in-
dividual amplifiers for the system become
increasingly severe.

For the New York to Boston project, a
microwave amplifier was developed using
already available velocity-modulation tubes.
This amplifier, using four stagger-tuned
stages, proved satisfactory for this service
and, in fact, tests indicated that this system
could be extended to considerably greater
distances and still give good performance.
It was apparent, however, that these ampli-
fiers would not be satisfactory for a coast
to coast system.

When this limitation became clear several
years ago, a study was undertaken to de-
termine which particular type of electron-
tube amplifier then known had the best
possibilities of being pushed to greater
gain-band products. The results of this
study indicated that a very promising way
was to build, for operation at 4,000 mega-
cycles, an improved planar triode, that is,
one in which the active elements are on
parallel planes.

In arriving at this conclusion, two general
types of devices were considered: velocity-
modulated, as in a klystron, and current-
modulated, as in a triode. In the usual
velocity-modulated devices, the bandwidth
is limited equally in both the input and out-
put cavity resonators; in the grounded grid
triode, on the other hand, essentially only
the output resonator limits, the input being
very broad. Consequently, as the band is
widened, the klystron loses gain at 6 db
per octave of bandwidth, while the triode
loses only 3 db per octave. If the two de-

vices start with equal gains at some narrow
bandwidth, the triode rapidly pulls ahead
in gain as the bandwidth is increased.

The relative possibilities of increasing the
gain, or transconductance, also seemed
better with a triode. According to the
simplest klystron bunching concept, the
transconductance of a klystron may be in-
creased indefinitely simply by making the
drift time longer. Unfortunately, this sim-
ple kinetic picture does not take account
of the mutually repulsive space-charge ef-
fects which set an upper limit to the useful
drift time by debunching the electrons after
a time. For a 2,000-volt beam in the 4,000-
megacycle range, this upper limit is approx-
imately three micromhos per milliampere.
The 402A tube used in the New York to
Boston system has already approached this
limit within a factor or two.

In a triode there is also an upper limit to
the transconductance that can be achieved

Fig. 1-The BTL 1553 microwave triode with
a cross-section drawing of it in the background

by spacing cathode and grid more closely.
This limit would be reached if the spacing
were so close that the velocity produced
by the grid voltage were of the same order
as the average thermal velocity of cathode
emission. The triode limit of some 10,000
micromhos per milliampere is, however,
many times greater than that for ordinary
klystrons. What is still more important is
the fact that previous microwave triodes
were still a factor of twenty to twenty-five
below this limit, leaving considerable room
for improvement. Thus, if mechanical meth-

looked more complex mechanically and
more speculative theoretically than a triode.

By translating the known requirements
on gain, bandwidth and power output into
specifications for the actual triode dimen-
sions, it was found that the input spacings
of existing commercial tubes would have
to be reduced by a factor of about five.
In addition, cathode emission current den-
sities would have to be increased about
three to four times. A design was evolved
in which the required close spacings could
be produced to close tolerances by methods

Fig. 2—Comparison
of the spacings of
the 1553 triode at
the right with a pre-
viously existing mi-
crowave triode at

ods could be devised for decreasing the
cathode-grid spacing and at the same time
maintaining parallelism between cathode
and grid, it seemed highly probable that
great improvements were available from a
new triode.

Improvements are possible in a klystron
by lowering the drift voltage, to whose
three-fourth power the transadmittance
limit is inversely proportional. To get trans-
admittance values anywhere near the
triode, however, would require low voltages
and close spacings somewhat like the latter.
Furthermore, the tube would be more com-
plex, having several grids instead of one,
and would encounter difficulties involved in
handling large currents in low-voltage drift
spaces. A number of modifications of klys-
tron operation was considered, but all

consistent with mass production require-
ments. The BTL 1553 tube was the result.

The electrode spacings of this tube and
of a commercially available microwave
triode are shown in Figure 2. In the 1553,
the cathode-oxide coating is 14 mil thick,
the cathode grid spacing is 6/10 mil, the
grid wires are 14, mil in diameter, wound at
1,000 turns per inch, and the plate-grid
spacing is 10 mils. It is interesting to note
that the whole input region of the 1553 in-
cluding the grid is well within the coating
thickness of the older triode.

The arrangement of the major active ele-
ments of the tube are shown in Figure 3.
This perspective sketch has been made
much out of scale so that the very close
spacings and small parts would be seen.
The nickel core of the cathode is mounted

in a ring of low-loss ceramic in such a man-
ner that the nickel and ceramic surfaces
may be precision ground flat and coplanar.
A thin, smooth oxide coating is applied to
the upper surface of the cathode by an
automatic spray machine developed espe-
cially for this tube. With this machine, a
coating of 14 mil +0.02 mil may be put on
under controlled and specifiable conditions.
To insure long life with such a thin coating,
it was necessary to develop coatings from
two to four times as dense as those used in
existing commercial practice.

The grid wires are wound around a flat,
polished molybdenum frame that has been
previously gold sputtered. The winding ten-
sion is held within +1 gram weight to
about 15 gram weight, which is about sixty
per cent of the breaking strength of the
wire. This is accomplished by means of a
small drag-cup motor brake, a new method
which was developed especially for these
fine grids. The grid is then heated in hydro-
gen to about 1,100° C, at which point the
gold melts and brazes the wires to the
frame. The mean deviation in wire spacing
is less than about ten per cent, and in fact
these grids are fine enough and regular
enough to be diffraction gratings as is
shown in Figure 5. In this figure, a fourth
order spectrum diffracted by one of these
grids can be seen. The third order, which
should be absent because the wire size is
about one-third of the pitch, is much less
intense than the fourth. Proper spacing of
the grid is then obtained by a thin copper
shim placed between the cathode ceramic
and the grid frame. Its thickness must be
equal to the coating thickness, plus the
thermal motion of the cathode plus the de-
sired hot spacing.

The cathode, spacer, and grid comprising
the cathode-grid subassembly are riveted
together under several pounds of force
maintained by the molybdenum spring on
the bottom of the assembly. The rivets are
three synthetic sapphire rods fired on the
ends with matching glass. In Figure 4, the
parts comprising this assembly are shown
in appropriate pile-up sequence at the left,
and the completed cathode-grid sub-
assembly is shown at the right between the
bulb and the press. The grid-anode spacing
of 10 mils is easily obtained by means of

an adjustable anode plug whose surface
is gauged relative to the bulb grid disc.

The high current density of 180 milli-
amperes per square centimeter, the thin,
dense cathode coating, and the very close
spacings posed a problem in obtaining ade-
quate emission and freedom from particle
shorts, and had to be solved by quality con-
trol methods because of the large number
of factors involved and the precision re-
quired. Tubes, subassemblies, and testers
have been made in batches and studied by
statistical methods. To achieve a state of
statistical control on emission, and freedom
from dust particles, it is necessary to proc-
ess the parts and assemble the tubes in a
rigorously controlled environment. Com-
pletely air-conditioned processing and as-
sembly rooms operating under rigorous
controls have been found necessary, and
will be described in a forthcoming article.
Under such controlled conditions, good
production yields with satisfactory cathode
activity have been obtained, whereas with-
out such conditions not only was the yield
low but it was difficult to ascertain just
what factors were operating to inhibit
emission and to cause cathode-grid shorts.

A summary of the pertinent low-fre-
quency characteristics of the 1553 triode is
given in Table 1. It should be noticed that
at plate currents of 25 milliamperes, the
transconductance per milliampere is about
2.000, that is, about one-fifth of the theoret-
ical upper limit. At lower currents this fig-
ure is higher: at 10 milliamperes, for ex-
ample, it is 3,000 micromhos per milliampere.
Diodes with the same spacings have about
twice these values of transconductance per
milliampere, showing that the grid is fine
enough to obtain fifty per cent of the per-
formance of an ideal grid.

A waveguide amplifier circuit for this
triode, developed by A. E. Bowen and
W. W. Mumford, provides resonant cavities
and coupling windows such that the ampli-
fier may be tuned and matched to wave-
guide over a frequency range from 3,700
to 4,200 megacycles per second.

With the d-c operating conditions given
in Table 1, the 4,000 megacycle amplifier
performance is as given in Table 2. The
performance of the 1553 triode in a modu-
lator circuit developed by Mr. Mumford

is given in Table 3. This performance is to
be compared with the 10 db loss obtained
in the New York to Boston relay with
crystal modulators requiring some 750
milliwatts of beating oscillator power.
The tube also works well as a harmonic
generator. In the present New York to
Boston system, reflex oscillators are em-
ployed to provide the local and transmitting
oscillator power. Buffer amplifiers are nec-
essary to provide frequency stability and to
raise the oscillator power level to that
needed by the crystal modulator. As an
improvement on this, D. M. Black has pro-
duced enough power for use as a 4,000
megacycle transmitting oscillator from a
chain of multipliers beginning with a piezo-

gm—50,000 pmhos pyf
p—350 Cy,=1.05 pyf
rp— 7,000 ohms Cxp=.005
TABLE 2—1553 AMPLIFIER AT 4,000
MEGACYCLES
Bandwidth ...... 120-170 megacycles
Noise Figure........ 16-18 db
Power Output...... 0.5-1 watt
TABLE 3—1553 MopuLator—65 To 4,000
MEGACYCLES
Bandwidth ........... 70-90 megacycles
Power Output ......... 10 milliwatts for less than

electric crystal oscillator at 40 megacycles.
The last stage of his array is a 1553 doubler
going from 2,000 to 4,000 megacycles with
a gain of from 0 to 3 db at an output level
of 300 milliwatts.

The properties of this new triode and its
ability to serve as amplifier, modulator, and
harmonic generator will make possible
long-distance radio-relay systems with
improved repeaters. Such new repeaters
will require no excessively high voltages
and fewer types of radio-frequency tubes,
and will use about half the power while
providing transmission characteristics which
have not heretofore been obtainable.

The triode is, of course, an old device.
This new type, however, well illustrates

how old ideas may sometimes be resur-
rected by means of new materials and tech-
niques to yield revolutionary results
compared to those of the past. The new
methods and techniques developed for the
1553, such as those for finer grids, metal-
ceramic assemblies, closer spacings, and
higher emission densities, are not limited
to triodes at 4,000 megacycles. These meth-
ods seem likely to find use in building better
tubes at low frequencies, and moreover to
aid in the development of newer tube types
at still higher frequencies.

The development of this microwave
triode has required not only the expert and
highly codperative services of a large team
of electrical, mechanical, and chemical
engineers but the indispensable assistance
of skilled technicians, all of whom worked
smoothly together to develop these new
materials and techniques to a point where
they are specifiable and amenable to quan-
tity production. It is not practical to men-
tion all those who have made significant

THE AUTHOR: Jack A. Morton graduated
from Wayne University in 1935 with a B.S. degree
in electrical engineering followed in 1936 by the
M.S.E. degree from the University of Michigan.
He joined the Laboratories in September of 1936
to work on coaxial cable and microwave amplifier
circuit research, and continued his studies in grad-
uate physics on a part-time basis at Columbia
University until 1941. During the first half of the
war he was a member of a group engaged in im-
proving the signal-to-noise performance of radar
receivers. In 1943 he transferred to the Electronic
Development Department to work on microwave
tubes for radar and radio relay. Last year he was
made electronic apparatus engineer responsible for
the development of Transistors and other semi-
conductor devices.

An organization as large as the Labora-
tories has problems of internal communica-
tion that do not appear in smaller groups.
It is important that the individual scientist
be able to bring his knowledge and per-
sonal views before his associates outside his
immediate area of work and of location. A
practical solution has been found in the
Laboratories through the use of the “Cover
Sheet for Technical Memoranda.”

Starting in a small way about twenty
years ago in a small research groupt work-
ing on carrier transmission, the use of the
Cover Sheet for Technical Memoranda, or
“MM” as it is now commonly called, has
spread to the Department, the General De-
partment, and finally to all of the technical
General Departments. With such a cover
sheet, the status of an MM is that of a tech-
nical exposition of his work by the individ-
ual engineer, and it carries only his personal
authority. There is no indication that a
supervisor is or is not in full accord with all
of the ideas expressed, although his advice
may have been sought before routing it.
The memorandum becomes a part of de-
partmental policy only when sent with a
covering letter and to the extent set forth
in the letter.

The routing list on the cover sheet cuts
across all department lines. Here the author
lists the names of individual engineers in
his own or other departments to whom he
believes the subject is of direct interest.
There may be only a few or there may be
several dozen. If he believes that a certain
group is or ought to be interested, but he
does not know the individuals concerned
or their responsibility, he may route a copy
to the group head. The engineer may con-
fer with his immediate supervisor as to the
general coverage of the list, but depart-
mental organization is ignored. The list
may include all ranks from a General De-
partment head to an individual engineer.

*Excerpted from a discussion prepared by R. C.
Mathes for presentation at the National Electronics
Conference in Chicago on November 5, 1948.

*#R. V. L. Hartley recalls that the first routing
sheet came from a discussion with J. Warren Hor-
ton of this group.

inevitable delays due to pressure of other
work and questions raised, which would
occur if interdepartmental transmission
were accomplished only by way of top
levels. Personal contact is encouraged be-
cause an engineer, on reading a report of
special interest to him, will reach for the
telephone to make an appointment for a
personal conference with its originator. His
object may be to seek further information
or to argue a divergent point of view, but
either way a new friendship or an improve-
ment in mutual interests generally results.

Our Filing Department keeps a complete
file, originally of cover sheets only, but now
on 3x5 cards, arranged by subject or class
of work. This makes available to an engi-
neer reviewing or reopening a line of work
a good brief guide to the more important
memoranda available. He also sees from
the names of the authors of the various
memoranda whom he should seek out first
for personal discussion. Adequacy of dis-
tribution is further insured by monthly cir-
culation of a list of titles and authors of all
Technical Memoranda. Several sets of cir-
culation file copies are maintained for use
on a reference basis to take care of requests
resulting from this circulation list. This
freedom of circulation is only rarely re-
stricted at certain stages of special jobs and,
of course, with work being done on classi-
fied Government projects.

From the independent status given tc the
Technical Memoranda, there are derived
benefits in addition to the original objec-
tives of dissemination of opinion. They be-
come to the individual engineer a medium
of internal publication to a large group of
his associates, not only of the results of
work done but also of his judgment of the
significance of his work and of his plans
and hopes for the future. They serve the
individual much as a radio set does the iso-
lated mariner, permitting him not only to
disseminate information that others may
need, and apprising others of information
that he himself requires, but enriching
his life and widening his field of interest
by a greatly extended range of personal
associations.

At the conclusion of World War II, the
Laboratories embarked on a program of
providing radio-telephone service to all
types of mobile equipment. Although the
major emphasis of this development effort
has been directed to providing this service
to automobiles, substantial progress has also
been made in making it available to rail-
roads as well. Experimental service be-
tween New York and Washington, for ex-
ample, was inaugurated* on August 15,
1947. It utilized land station equipment
operating in the frequency band from 152
to 158 megacycles that had already been
located at sites suitable for providing urban
radio-telephone servicet in the cities be-
tween New York and Washington. It was
evident, however, that such a system could
not be employed for railroad systems whose
tracks neither traversed nor passed near
cities spaced at regular intervals and having
urban mobile installations. Such service
was practical, however, where the railroad
routes paralleled highways over which
radio-telephone service,{ operating in the
frequency band from 35 to 43 megacycles,
had already been provided. At these lower
frequencies, however, the antennas are in-
herently longer, while the available height
above the top of the car is severely limited
by tunnels and other structures under which
the trains must pass.

To tie in with either the existing urban
or highway radio-telephone systems, it is
necessary for the antenna to be an efficient
radiator of a vertically polarized wave hav-
ing a uniform pattern in the horizontal
plane. The simplest type of antenna to
meet these electrical requirements is a ver-
tical rod or whip approximately a quarter
of a wave length in height at the operating

frequency, and mounted over a flat con-
ducting surface. This would require a
height at urban frequencies of about
eighteen inches, and at highway frequencies
of about sixty-eight inches for transmitting
and eighty-three inches for receiving. These
heights are all too great for railroad use,
but methods of somewhat reducing the
height are known.

Fig. 1—Relationship between total radiation resist-
ance of an inverted L antenna and the ratio of the

For the first railroad application, between
New York and Washington, sufficient height
was available for a special vertical antenna
by mounting it at the end of the car where
the top slopes downward, but there was no
assurance that there would be room for
this antenna on all lines even at urban fre-
quencies. At highway frequencies, an an-
tenna of this type was entirely unsuitable.

Permissible heights above the top of the
car are rarely over sixteen inches and may
be considerably less. They vary with dif-
ferent roads and with the particular routes
over which the cars will be operated.
Height, however, is not the only restric-
tion. Railroads commonly require that any
structure on top of the car be strong enough
to support a man’s weight, and on electri-
fied roads, the antenna must be well
grounded to the car and must have suffi-
cient cross-section to carry safely the large
currents that might flow should the over-
head trolley wire come in contact with it.
With such requirements to be met, flexible
whip or spring-mounted rod antennas are
ruled out on all three counts of height,
strength, and size.

One of the earliest problems in radio
broadcasting was to develop an efficient
vertically polarized antenna that was con-
siderably shorter than a quarter wave
length at the operating frequency, since at
broadcast frequencies a quarter wave length
may be upwards of 400 feet and hence struc-
turally difficult. One of the simplest solu-
tions to this problem turned out to be a
vertical mast considerably shorter than a
quarter wave length, insulated at the bot-
tom, and capacitance loaded by a horizontal
element at the top of the mast. Such ar-
rangements are known as inverted L-type
antennas.

Their over-all length, including both hori-
zontal and vertical sections, is about one-
quarter wave length. They are resonant
antennas, which means that the input im-
pedance is essentially a pure resistance.
For such antennas, which were considered
for railroads at an early date, the input
impedance is nearly the same as the radia-
tion resistance. The bend in the antenna,
where it changes from vertical to horizontal,
may be made at any point, but its radiation
resistance varies with the relative length
of the vertical section, as shown in Figure
1. Regardless of the position of the bend,
practically all the radiation takes place
from the vertical section; as a result, an-
tennas of this particular type are suitable
for railroad application.

On mobile installations, it is usually de-
sirable to connect the antenna to its asso-
ciated equipment by some form of standard

Fig. 2—A folded antenna developed for the
frequency range from 152 to 158 megacycles

flexible coaxial cable. Such cables of 50-
ohm and of 70-ohm nominal impedance
are readily available commercially. With
an inverted L antenna operating at highway
frequencies, however, the vertical section
would have to be less than one-quarter the
total length to secure a low enough height,
and with the bend occurring so low, the
resistance is very low.

Some form of transformation is required,
therefore, to match a low impedance in-
verted L antenna to its connecting cable.
One means of accomplishing this is to
double the length of the inverted L antenna,
bending it back on itself in such a fashion
as to provide two spaced parallel elements
and bonding the end that is not connected
to the equipment firmly to the ground
plane. This procedure results in an antenna
like that shown in Figure 2, which was de-
veloped for railroad use in the band from
152 to 158 megacycles. Folding an antenna
back on itself in this manner increases its
input impedance approximately as_ the
square of the number of parallel elements,
and thus four times for the antenna shown.

To match a 50-ohm line, the inverted L
prototype of such an antenna would have
to have an input impedance of 12.5 ohms,
and from Figure 1, it will be seen that this
resistance is obtained when the vertical

Fig. 3—For the frequency range from 35 to 43 mega-
cycles a three-element folded antenna was developed

length is about thirty-five per cent of the
total length. For urban frequencies, where
the over-all length is about nineteen inches,
this gives a satisfactory height and the an-
tenna of Figure 2 is of approximately these
proportions. It is in use at the present time
on the Broadway Limited.

An antenna designed in similar fashion
for highway frequencies would exceed two

feet in height and thus could not be used.
It was necessary, therefore, to devise some
way of obtaining a higher transformation
ratio. By using three parallel elements, as
shown in Figure 3, a transformation ratio
of about nine was obtained. This required
an impedance of 5-5/9 ohms for the in-
verted L prototype in order that the folded
antenna might match a 50-ohm coaxial. As
may be seen from Figure 1, this input im-
pedance is obtained with an antenna having
a vertical section about twenty per cent of
the total, and this brings an antenna for the
highway frequencies within the required
limits of height. When actually built, the
antenna impedance was found to be some-
what higher than the design value and
consequently a 70-ohm coaxial is used to
connect it to its associated equipment.

As evident from Figure 3, the two outer
legs of this antenna are firmly grounded
to the base, while the middle leg is insu-
lated and connected to the coaxial lead con-
nector. All three legs are connected to-
gether at the far end, and since the over-all
length is very critical, a trombone section
is employed to give the necessary adjust-
ment. After the proper adjustment has been
secured by sliding the end section in or out,
it is soldered in the proper position. An
antenna of this type on a car of the 20th
Century Limited is shown in Figure 4.

In this rather extreme design, where the
vertical elements make up such a small
proportion of the total antenna, the radia-

Fig. 4—A three-ele-
ment antenna on the
top of one of the cars
y of the 20th Century
Limited

tion efficiency of the antenna is down 1 db
with respect to a quarter wave whip be-
cause of the fact that part of the radiation
resistance is developed in the horizontal
portion of the antenna. In addition, it is
down 0.4 db because its pattern is essen-
tially that of a vertical antenna that is short

compared to a quarter wave length. Tests
have indicated that the over-all radiation
efficiency of the antenna is about 1.5 db
down with respect to a quarter wave whip.
A corresponding figure for the folded an-
tenna for the range from 152 to 158 mega-
cycles, shown in Figure 2, is 0.5 db.

THE AUTHOR: wW. C. Bascock received an
A.B. degree from Harvard University in 1920 and
a B.S. in Communication Engineering from the
same university in 1922. He joined the Develop-
ment and Research Department of the American
Telephone and Telegraph Company in 1922, com-
ing to the Bell Laboratories with that organization
in the 1934 consolidation. His work has been
largely concerned with inductive interference
problems between open-wire telephone circuits.
During the war he was engaged in radio counter-
measure problems for the National Defense Re-
search Committee. Since that time he has been
working on antenna development problems in con-
nection with mobile radio systems.

In the three and a half years since World
War II, the Bell System has gained more
than 10,000,000 telephones. This compares
with the more than 45 years it took the
System to attain its first 10,000,000 tele-
phones, and brings to approximately
32,000,000 the total number of Bell tele-
phones in service at the end of March.

The 10,000,000 mark in post-war gain is
a significant milestone in the Bell System’s
biggest expansion and service improvement
program in history. Despite the fact that
telephones are being added at the rate of

some 200,000 a month, the continuing heavy
demand for service is such that more than
1,000,000 orders still remain to be filled. Of
the 10,000,000 Bell telephones added since
V-J Day, more than 1,000,000 have been
installed in rural areas, where the net gain
has averaged about 1,000 every working
day. In the last eight years, the proportion
of farm homes with telephones has nearly
doubled. About forty-five per cent of all
farms in the country now have telephones,
as compared with twenty-five per cent in

Almost every switching circuit in a local
dial office requires at least one timed inter-
val. Typical examples are charge delay,
which prevents falsely charging the sub-
scriber when a line-busy or overfiow condi-
tion is encountered; permanent signal time-
out, which prevents senders and registers
from being held busy indefinitely; and coin
collect and return, which insure sufficient
timing for coin magnet operation. A large
common-control circuit may employ ten or
twelve different timed intervals. A 10,000-
line central office of the No. 5 crossbar type
may have 3,000 or more delay circuits to
provide these timing intervals. Since such
circuits are subject to variation as their
tubes and thermal structures age, it has
been felt desirable to develop testing appa-
ratus that would permit time intervals to
be measured as part of the central-office

Fig. 1—-W. H. Burgess using the electronic timing test
set in the crossbar laboratories

maintenance routine. The set developed is
shown in Figure 1. Its usefulness is not lim-
ited to maintaining timing circuits, how-
ever. Another important application is in
measuring the operate and release times of
relays. Wherever short time intervals are
to be measured, the electronic timing test
set provides a fast and convenient method.

In the course of developing a slow-acting
relay a few years ago, it was necessary to
make a large number of measurements of
operate and release times. Since the avail-
able methods of time measuring were not
entirely satisfactory for this work, E. R.
Morton of Switching Apparatus Develop-
ment designed an electronic timer that gave
a direct reading of time in milliseconds on
an indicating meter. Its operation was
based on charging a capacitor from a con-
stant current source. Ten or twelve of these
test sets were built for use in the Labora-
tories, and one is shown in operation in
Figure 2.

Based on the same general principles,
but arranged for a somewhat different set
of conditions and time intervals, the new
timing test set was developed for more gen-
eral application. It is arranged to connect
directly to any 48-volt central-office circuit,
and its timing is started and stopped by the
various potentials encountered on the con-
tacts of the apparatus under test. These are
—48-volt, ground, or open-circuit, and the
new test set is designed to start and stop
timing with any of the six possible permu-
tations of these three conditions. The only
power connection required is 48-volt cen-
tral-office battery, which is available from
test jacks on all frames. Two miniature B
batteries and one flashlight cell, incorpo-
rated in the set, complete the power re-
quirements. Time ranges provided are 0-20,
0-100, 0-500, and 0-5,000 milliseconds.

The essential elements of the timing cir-
cuit are indicated in Figure 3. Timing is

started by applying ground to the grid of
the CH tube and is stopped by applying
—13 volts. Plate voltage on cH consists of
90 volts from one of the B batteries in the
set minus the voltage across the capacitor
c, which increases as the capacitor charges.
Except at low plate voltage, plate current
of the pentode cu increases very little with
increase in plate voltage, and the change
in the plate voltage due to the change in
the voltage across the capacitor as_ it
charges is made small enough, relative to
that of the B battery, so that the plate cur-
rent remains constant to within the preci-
sion of the set throughout the charging of
the capacitor. With negative voltage on the
grid of cu, no plate current is flowing, and
the capacitor is fully discharged through
contact s so that the voltage across it is
zero. At the start of a time measurement,
contact s is opened, and ground is applied
to the grid of cu, thus starting the flow of
the constant plate current through the ca-
pacitor which is in the circuit.

The voltage across the capacitor at any
time is equal to its charge Q, divided by its
capacitance: v—Q/c. When the capacitor is
charged at constant current, the charge, in
turn, is equal to the constant charging cur-
rent times the time during which it flows:
Q ir. By substituting this expression for
charge into the above expression for volt-
age, it will be seen that the voltage is given
by the expression: v=rr/c. Since both 1

This voltage is measured by the vacuum-
tube voltmeter circuit shown at the right of
Figure 3. The meter m indicates time di-
rectly on the 100-millisecond scale; a con-
stant multiplier is used for the other scales.
At the end of the time interval being meas-
ured, —13 volts is applied to the grid of
cH, which at once stops passing current,
and the indication of the meter at this time
gives the duration of the time interval be-
ing measured.

The time indicated by the meter m will
be correct, of course, only for one value of
charging current, and it is necessary, there-

fore, to provide some means of insuring
that the charging current is of the correct
value before a set of measurements is made.
A very ingenious method of calibrating was
suggested by J. T. L. Brown of the switch-
ing research group.

In the equation for the voltage drop
across a resistor with a constant current
flowing through it, v=rt1, the values of v
and 1 will be the same as in the expression
for the voltage across a capacitor after it
has been charged for a time T at a constant
current 1, v=1T/c, if R is made equal to r/c.
If, therefore, a resistor of value T/c is put
in place of the capacitor in Figure 3, the
meter will indicate the time T when the cur-
rent through the resistor is 1.

In taking advantage of this fact for cali-
brating the test set, a resistance of the
above value is put in place of the capacitor
by operating the tst key to the caL posi-

tion, and then adjusting the potentiometer
p until the meter indicates T—full scale be-
ing used for this value of tT. In the actual
test set, there are functionally four capaci-
tors and four resistors corresponding to the
four ranges of the indicating meter, and a
voltage-range selector on the front of the
test set connects in the desired pair accord-
ing to the time interval to be measured.

Connections to the circuit to be tested
are made by a three-conductor cord with
clips on one end to connect to the circuit to
be tested and a plug on the other to con-
nect to a jack on the test set. Two of the
conductors of the cord are used for starting
the time cycle in the apparatus, while the
third, or tip lead, will be connected to a
lead in the circuit under test on which will
appear the conditions that indicate the be-
ginning and end of the time period. How
these leads of the cord would be connected
to one type of electronic timing circuit is
indicated in Figure 4. Normally, the cath-
ode and starting anode of the cold-cathode
tube are held at the same potential by the
back contact of relay u1, and the tube will
not be conducting. When relay u1 is oper-
ated, however, the starting anode is discon-
nected from the cathode, and capacitor c1
will start charging through resistor r1 from
130-volt battery. The voltage across the ca-
pacitor is applied to the starting anode of
the tube, and when it reaches the ionizing
potential, the tube will pass current and
thus operate relay v2.

The beginning of the time period is
marked by the closing of the operating cir-
cuit of relay u1, and at this instant the tip
lead of the cord will be open-circuited. At
the end of the time period, ground will be

applied to the tip lead. In other types of
circuits, the indications for the beginning
and end of the time period may be any of
the six combinations already referred to,
and the beginning of timing may require
the opening of the ring and sleeve leads in-
stead of their closing as in Figure 4.

In its normal position, a key marked tsr
on the front of the test set closes the con-
tact s on Figure 3 to hold the timing ca-
pacitor discharged, and the cu tube will be
non-conducting. When thrown to its CAL
position, the tst key sets up the calibrating
conditions to permit the constant current
to be adjusted as already described. When
it is thrown to its opr position, it connects
the timing capacitors instead of the cali-
brating resistor into the circuit, opens the
contact s, operates a relay that either opens
or closes the ring and sleeve leads of the

Fig. 5—Typical circuit conditions requiring the
five selector positions

test cord, depending on whether a sENp key
is in the Bk or MK position, and closes the
test set, there are functionally four capaci-
tors and four resistors corresponding to the
four ranges of the indicating meter, and a
voltage-range selector on the front of the
test set connects in the desired pair accord-
ing to the time interval to be measured.

Since the capacitor of Figure 3 must be-
gin or stop charging when any of the six
possible permutations of ground, open-cir-
cuit, and —48 volts are encountered on the
test lead, circuit elements are incorporated
in the test set in addition to those shown in
Figure 3 to convert the ground, open-cir-
cuit, or —48 volts to either ground or —13
volts on the grid of the cu tube. These in-
clude two tubes marked c and In and are
shown in Figure 6.

Before starting a test, the test-condition
selector on the front of the test set is moved
to the position corresponding to the start
and stop-timing conditions that will be en-
countered in the circuit being tested. Al-
though there are six such conditions pos-
sible, the selector has only five positions,
since the fifth position takes care of two
situations. Table 1 shows the five positions
of this selector, and the six start and stop
conditions they take care of. In Column 4
of this table is given the position of K in
Figure 6 that the selector establishes.

With the selector in positions 2, 3 and 5,
the start and stop-timing conditions that are
encountered in the circuit under test are
correct to start and stop the charging of
the timing capacitor of the test set. With
the selector in positions 1 or 4, however, the
stop-timing conditions are correct, but the
start-timing condition in both cases is

open-circuit, and when the tT lead encoun-
ters an open circuit, the timing capacitor is
not charging, as already pointed out. In
these two positions, therefore, the selector
closes either the c or D contacts of Figure
6, as indicated in Column 5 of Table 1.
When the starting of timing requires that
the operation of the op relay close the con-
nection between the ring and sleeve con-
ductors, key senp of Figure 6 will be in the
MK position, while when it requires that the
ring and sleeve connection be opened, the
SEND key will be in the Bx position.

Typical connections and the correspond-
ing positions of the condition selector for
measuring the operate and release times of
relays are shown in Figure 5. For condi-
tions 3 and 5, the senp key will be in the
BK position, while for the others it will be
in the MK position.

A front view of the test set is shown in
Figure 7. The condition selector is at the
left, and the meter-range selector at the
right. In the lower center are three keys:
the tst key at the left, a battery key to
connect power to the set in the middle, and
the sEND key at the right. Just above these
keys at the left and right are two poten-
tiometers. One controls the adjustment of

Position of Begin End Switch Auxiliary
Selector Timing Timing K Contacts
0( —48) G A Cc
2 —48 v G A -

the charging current while the set is being
calibrated, p of Figure 3, and the other per-
mits adjusting the meter to read zero when
there is zero voltage across the timing ca-
pacitor. At the extreme upper left are four
jacks: two for the test cord, one for the
power connection, and one used in testing
the ring-up time of 1,000-cycle toll ringing.

The set also provides means for testing
the operation of its three tubes by using the
Tr position of the sENp key, and for meas-
uring the time interval between the closing
or opening of the ring and sleeve leads and
the connection of the T lead of Figure 6 to
the tip lead of the jack. The op relay is ad-
justed so that this latter connection always
precedes the closing or opening of the ring
and sleeve, but the interval is short and
need be taken into consideration only in
special cases. The mcr key, which is shown
at the extreme upper right of the test set,
is used for this purpose.

The applications illustrated above are
only a few of the many for which this set

THE AUTHOR: M. E. Krom was graduated
from Purdue University with the degree of B.S. in
E.E. in 1923. He joined the Laboratories imme-
diately after graduation and spent the first two

may be used, and are given primarily to
show the application of the test set to the
measurement of time under typical and
varied circuit conditions.

years in the panel dial laboratory. Then followed
six months of relay design after which he was
transferred to a laboratory group which handled
ringing and tone studies. Then he transferred to a
group concerned with means of measuring and
suppressing radio interference. In 1932 this work
became a function of the ringing and tone studies
group. Mr. Krom was transferred at that same
time to continue radio interference tests, and the
development of radio filters and their application
to telephone equipment. This, in combination with
ringing and tone studies, occupied his time until
the summer of 1941 when he was assigned to a
defense project. Shortly before the outbreak of
war, he was transferred to the Transmission De-
velopment Department, where he was concerned
principally with the development of radar test
equipment. In October 1945 he returned to the
Systems Development Department, and has since
been associated with the design of No. 5 crossbar.

Various nomographs, charts, and calcula-
tors are available for the calculation of the
inductance of coils, but most of these
graphical aids do not cover the range of
values of interest to the designer of coils
for television, f-m, and radar i-f frequencies.
The nomograph shown below, reprinted
from an article by J. H. Felker in the March
issue of Electronics, has been designed to
fulfill this need. Unlike other coil nomo-
graphs, it gives in one operation the num-
ber of close-wound turns required to get
a desired inductance.

where r is the radius of the coil in inches,
l its length in inches, and n the number of
turns. In close-wound coils, | is a function
of n. Substitution of nd, where d is the

diameter of the wire in inches, for | in
Equation | gives an equation which can be
solved for n to give:

The complexity of Equation 2 accounts for
the unusual structure of the nomograph
and indicates the computational labor
avoided by its use.

where D is the diameter of the coil in centi-
meters, N is the number of turns, and S
is the ratio of the length of the coil to its
diameter. Changing the centimeter dimen-
sions of D in Equation 3 to inches and em-
ploying Wheeler’s symbols gives:

quired number of turns on other set of curves.
Example—How many turns of number 30
wire are required on a 0.25-inch diameter coil

4,
5 SS 15 &p
4 SS SS SSS Om
SSS
2 \\\
\\Y
15
5
1.0
09 0.15
08
0.2
Lo
a \ \ 0.25
5 09 \ 03
08 i COIL FORM DIAMETER IN INCHES
: a How to use the nomograph—Place straight- form to obtain 0.7 microhenry? Run straight-
edge on desired values of inductance and wire edge between 0.7 on left-hand vertical scale and
size on the two vertical scales. Where curve 30 on right-hand side of right-hand vertical scale,
06 for diameter intersects straightedge, read re- as indicated by thin dashed line. Trace upward

along 0.25 diameter curve to straightedge, and
read 10 turns as value of other curve passing
through this intersection.

Amplifiers for the L1 carrier system* are
mounted in sealed containers of the plug-in
type, and the repeaters of which they form
a part are mounted in huts or manholes
about eight miles apart. Maintenance pro-
cedures used with voice or low-frequency
carrier circuits, where the repeaters are
mounted on open panels in repeater sta-
tions, are not applicable because of the fre-
quency band involved and the critical ad-
justments required. When trouble occurs
in an L1 amplifier, a spare unit is plugged
in its place, and the defective amplifier is
taken to a regional amplifier servicing cen-
ter, where the necessary test sets and tools
are available to permit the amplifiers to be
unsealed, inspected, repaired, and com-
pletely tested before they are returned to
spare stock. Careful checking of the vac-
uum tubes and the replacement of defec-
tive or worn-out tubes is an important part
of the servicing procedure. The recently de-
veloped J68798C vacuum-tube test set
which is shown in Figure 1 is provided for
this purpose.

Below the writing shelf of this unit are
two regulated rectifier panels serving as
power supplies, while at the top is a power
distribution panel, where the a-c power is
connected to the test set through a voltage
regulating transformer, and where the light-
ing fixture at the top of the bay is con-
trolled. Immediately above the shelf are the
six major testing panels, shown in greater
detail in Figure 2. The basic tests are for
transconductance, plate current, cathode
activity, and grid-to-cathode insulation, and
they are all carried out by the first four
panels above the shelf.

The lowest of these panels is the ampli-
fier connecting panel, which carries a
bracket-mounted circular shelf with a re-

ceptacle to take the power plug of the am-
plifier. After an amplifier to be tested has
been unsealed and its cover removed, it is
plugged into this shelf and clamped in po-
sition. The shelf is connected to its mount-
ing bracket through a ball-and-socket joint
to permit the amplifier to be turned or
tipped to any position that will give easiest

access to the internal leads to which the
test voltages will be applied. This permits
any tube soldered in its particular stage lo-
cation in an amplifier to be tested in place.
A flexible cord connects the power recep-
tacle of the shelf to the amplifier connect-
ing panel, and other test cords, plugged
into jacks on the oscillator-detector panel,
are used to connect to the necessary points
in the amplifier circuit. This feature facili-
tates screening of tubes in an amplifier un-
der repair, and avoids the unnecessary re-
moval of tubes good for further service.

Tubes that have been removed from the
amplifier may be tested by inserting them
into sockets in the individual tube test
panel—which is between the amplifier con-
necting and the oscillator-detector panels.
An adapter is provided that allows unbased
tubes of the 384A and 386A types also to
be tested. In addition, means are provided
on this panel for measuring the grid-to-
cathode insulation. Plate and screen-grid
voltage, grid bias, heater voltage, and d-c
plate current for a test are indicated di-
rectly on the meter panel.

The principal test circuit, shown in Fig-
ure 3, is provided on the oscillator-detector
panel—third above the shelf. It includes an
oscillator generating a 4-kc signal that is
fed through a fixed pad to the grid of the
tube under test and also to the CAL point of
the comp key. A 10 db pad, controlled by a
second key on this panel, is also provided
in the oscillator output circuit for measur-
ing higher transconductance tubes with a
reduced input signal to the tube under test.

The detector circuit consists of an ampli-
fier, a varistor for rectifying the output sig-
nal, and a d-c milliammeter calibrated from
—6 to +2 db. During a measurement, the
DB-GM dial is turned until the meter reads
within 0.5 db of zero, when the transcon-
ductance may be read directly from the
dial. Meter readings other than zero are
used when the transconductance is less
than 1,000 micromhos or greater than 30
db above 1,000.

Two other essentially independent test
panels complete the test bay. A short-open
tube test panel immediately above the
meter panel provides means of detecting
an internal short or open circuit within a
tube and indicates the fault path. The posi-

Fig. 2—The six major test panels of the test set.
Reading up from the writing shelf, they are
designated: amplifier connecting panel; indi-
vidual tube test panel; oscillator-detector panel;
meter panel; short-open tube test panel; and
cold-cathode tube test set

tive identification of the nature of internal
faults within a specific tube removed from
an amplifier is often useful in isolating
troubles in the amplifier circuit elements
associated with such a tube. The essential
features of this circuit are indicated in Fig-
ure 4. The circuit consists of five 313C gas-
filled tubes which have one electrode of
their starter gap connected through resis-
tors to one side of a 120-volt a-c power
supply, and the other electrode of the
starter gap connected to one of the ele-
ments (except the cathode) of the tube
under test. The other side of the 120-volt
a-c circuit connects to the cathode and also
to the moving arm of a six-point selector.
Points 2 to 6 of this selector connect to the
same tube elements as do the gas tubes,
while the No. 1 point is left unconnected.
The tube to be tested is inserted into one
of the available sockets on the panel and
heater current applied.

The starter gap of the 313C tube con-
sists of two semi-circular electrodes visible
from the end of the tube. The main anode,

Fig. 3—Simplified schematic of the circuit of the oscillator and detector panel

in the form of a wire, projects between the
other two electrodes in a glass tube, but is
not used for this test circuit. When a volt-
age above the ionizing potential is applied
across the starter gap, current passes, and
the positive electrode will glow. With these
indicator tubes connected as in Figure 4,
with the selector switch in position 1, and
with no shorts or opens in the tube under
test, the left-hand anode of the indicators
connected to the plate and the grids will
glow, since the indicator tube will conduct
only during the half cycles of the power
supply voltage that make the left-hand elec-
trode positive. Current flow in the opposite
direction is blocked by the rectifying action
of the tube under test. Had any of the ele-
ments been open-circuited, the indicator

not have glowed. Had any of the electrodes
been short-circuited to the cathode, how-
ever, both electrodes would have glowed,
since the rectifying action of the tube under
test is by-passed by the short circuit. Shorts
between one element and any of the others
except the cathode are determined by ro-
tating the selector successively through its
six points. If, for example, there were a
short between the plate and G1, both sides
of the indicators for G1 and p would glow
with the selector on either step 2 or 5. A
table is provided for use with the set that
shows the glowing conditions for indicator
tubes for all possible short or open-circuit
combinations that can occur.

The remaining auxiliary panel tests West-
ern Electric cold-cathode and voltage regu-
lator tubes, both octal and miniature based,
and a hot-cathode diode (381A), which is

used in L1 carrier systems. This test circuit,
indicated in Figure 5, supplied with high
voltage from one of the rectifiers, makes
simple d-c breakdown and sustaining volt-
age measurements of a tube, while a milli-
ammeter with potentiometer controls en-
ables conduction current to be evaluated.

The test set was designed with a dual
objective in view: first, to provide sufficient
tube tests to insure satisfactory field per-

THE AUTHOR: A. A. Hesertein received
the B.S. degree from the City College of New York
in 1921 and then took graduate work at Brooklyn
Polytechnic Institute, receiving the E.E. degree
in 1923. In 1922, while completing his studies at
the Brooklyn Polytechnic Institute, he joined the
D & R where he engaged in the development of
carrier systems and in vacuum-tube testing prob-
lems. Since 1932, he has been concerned with
special long-range field trials of improved tubes
in voice frequency and carrier systems, vacuum-
tube test sets, and in general vacuum-tube appli-
cation, testing, and field maintenance problems.

formance of the tubes in repaired coaxial
amplifiers, and second, to provide essential]
tests under standard operating conditions
that are similar to manufacturing tests and
may be used for acceptance tests by the
Operating Companies. Experience with this
set in various amplifier servicing centers in
the field has demonstrated its usefulness in
insuring dependable tube performance in
repaired coaxial amplifiers.

Patents Issued to Members of the Laboratories by the United States Patent
Office, December to March, Inclusive

. R. D'Heedene
. C. Dickieson
. 8. Dubuar (2)
Edson
. Edson
gerton
. B. Ellwood
B. H. Feldman
. B. Ferrell (2)
Garvin
. E. Germanton
. A. Giroud
. H. Goldsmith
. I. Green
. B. Haines
. W. Harrison
. V. L. Hartley
E. Haworth
. Hecht

Recently, L. A. Wilson, President of the
American Telephone and Telegraph Company,
visited the West Street Laboratories and was
shown some of the latest technological achieve-
ments by O. E. Buckley. Gus Pasquarella,
staff photographer for The Saturday Evening
Post, took advantage of the visit to make pic-
tures of the pair for an article on Mr. Wilson
which appeared in the March 19 issue under
the title The World’s Biggest Business Gets a
New Boss. R. L. Shepherd of Publication made
this picture of Pasquarella photographing Mr.
Wilson and Dr. Buckley as they inspected auto-
matic message accounting equipment.

Pasquarella is an old friend of the Labora-
tories, for he spent two weeks at West Street
and Murray Hill, taking the pictures used to
illustrate the series of three articles which
the Post published concerning the Labora-
tories in May 1947, under the title Ma Bell’s
House of Magic.

Jack Alexander, an associate editor of the
Post, who wrote the article on Mr. Wilson, also

visited both West Street and Murray Hill in
assembling material and talked with, among
others, Dr. Buckley, W. H. Martin, Ralph
Bown, J. W. McRae, A. F. Bennett, R. K.
Potter, R. M. Burns, J. R. Townsend, Harvey
Fletcher, H. T. Friis and R. K. Honaman.

Dr. Harish-Chandra of Allahabad, U. P.,
India, who has done considerable research on
the theory of elementary particles at the Insti-
tute for Advanced Study, Princeton, N. J.

Dr. James A. Jenkins of Toronto, Ontario,
who has been engaged in research on matters
related to topological mapping problems at
Harvard University.

Dr. Robert Karplus of West Newton, Mass.,
who has been participating in nuclear research
at the Institute for Advanced Study, Princeton.

Dr. Joaquin Mazdak Luttinger of New York
City, who has been doing research work in
Zurich, Switzerland, on the theory of the super-
conductive state and who plans to continue
these studies in this country.

Dr. David Emerson Mann of Minneapolis,
who has been engaged in quantum mechanics
research at the University of Minnesota.

Harvey Winston of Tottenville, Staten Is-
land, who plans to do crystallographic research.

The Jewett Fellowships are designed to
stimulate and assist research in the fundamen-
tal physical sciences and particularly to pro-
vide the holders with opportunities for indi-
vidual growth and development as creative
scientists. They are awarded on recommenda-
tion of a committee consisting of seven mem-
bers of the Technical Staff of the Laboratories.
Primary criteria are the demonstrated research
ability of the applicant, the fundamental im-
portance of the problem he proposes to attack
and the likelihood of his growth as a scientist.
The awards are designedly post-doctorate and
only scientists who have recently received doc-
tors’ degrees or who are about to receive them
are normally considered.

Claude E. Shannon received the 1949 Morris
Liebmann Memorial Prize of the Institute of
Radio Engineers on March 9 at the award
dinner which culminated the Institute’s annual
convention.

The award is a cash sum of money and is
regarded as one of the outstanding honors of
the scientific world. It was presented to Dr.
Shannon by Stuart L. Bailey, president of the
Institute, “for Dr. Shannon’s original and im-
portant contributions to the theory of the trans-
mission of information in the presence of noise.”

Also honored at the award dinner were Dr.
Ralph Bown, Director of Research, who was
named last fall to receive the Institute’s highest
honor, 1949 Medal of Honor; and H. A. Affel,
who was made a Fellow of the Institute. Dr.
Bown received the award* “for his extensive
contributions and substantial and important
advancements in the art of radio communi-
cations.”

Dr. Shannon, who has been a member of
the Technical Staff of the Laboratories since
1941, is a native of Gaylord, Michigan. He re-
ceived a B.S. degree in E.E. from the Univer-
sity of Michigan in 1936. In 1940, he received
an M.S. degree in E.E. and a doctor’s degree
in mathematics from Massachusetts Institute of

C. E. Shannon of Physical Research receives
the Morris Liebmann Memorial Prize from
Stuart L. Bailey, president of the I.R.E.

Technology. Prior to joining the Bell System,
he was a National Research Fellow at Prince-
ton University, and served as a National De-
fense Research consultant.

In 1940, Dr. Shannon was awarded the AIl-
fred Nobel Prize by the American Institute of

Electrical Engineers. He is a member of Sigma
Xi, national scientific honorary fraternity, of
Phi Kappa Phi, the American Mathematical
Society and the I.R.E. His work in the Re-
search Department has been concerned with
switching and communication theories and
with computing machines.

A new sound system in the Murray Hill
Listening Room and Auditorium was recently

completed, and on March 11 a _ noon-hour
program was given to demonstrate the facili-
ties. On this occasion, doors to the Auditorium
had to be closed to many because of the stand-
ing-room-only interest in the affair, and critical
approvals, following the half-hour musicale,
were pointed to the effect that the new system
is the best that exists in the eastern section of
this country.

To show the range of the tonal values, play-
backs were made from recordings of recent
Telephone Hour broadcasts. These included
full orchestra, violin and speech. Highlight of
the demonstration was a piano solo presented
from the Auditorium stage by W. F. Kannen-
berg. The Chopin “Polonaise” which he played
was recorded and then immediately played
back over the system with complete fidelity to
the original.

Audio facilities people in charge of the
sound facilities were W. J. Brown, L. B. Cooke,
J. Z. Menard and E. V. Kuzela.

Inspecting a 310-type switchboard plug with molded
insulation are F. W. Hennessey of Western Electric,
D. G. Blattner, J. F. Baldwin and R. A. Hecht of Bell

On March 28 at West Street and on March
31 at Murray Hill, A. F. Bennett, director of
Station Apparatus Development, told of the
work which led up to the new 500-type com-
bined telephone set which is described on page
165 of this issue. Its predecessor, the 302-
type, which went into production in 1937,
represented the state of the fundamental arts
up to perhaps 1935. By the end of World
War II, enough advances had been made
to justify integrating them into a new model.
While Mr. Bennett’s department carried most
of the load, they drew heavily on Transmission
Apparatus for coils, capacitors, ballast lamp,
and cords, on Electronic Apparatus for varis-
tors and thermistors, on the Materials engi-
neers for the latest information on plastics and
finishes, and on the Magnetics people in con-
nection with the receiver and the ringer. Many
contributions to the final design were made by
Western Electric engineers, as a _ result of
discussions of the manufacturing and design
problems with the Laboratories’ engineers.

The Northern New Jersey Section of the
I.R.E. held an evening meeting on March 23
in the Arnold Auditorium. H. T. Budenbom

was program chairman for this event and K. K.
Darrow the chief speaker. He chose for his
subject Nuclear Fission and the Atomic Pile.

On March 25, over one hundred members
of the Metropolitan Section of the American
Physical Society attended the spring meeting
at Murray Hill, where they were welcomed by
O. E. Buckley. Following Dr. Buckley’s ad-
dress, a series of papers was given, including
one by W. E. Kock on Wave Propagation in
Dipole Arrays.

W. H. Martin talked to a group of the head-
quarters organization of the New England
Telephone and Telegraph Company on March
31 in Boston. His general topic was the opera-
tion of the Laboratories on a development
project, and he used the new combined set as

Although it has long been the Medical De-
partment’s practice to offer a chest X-ray to
all who have a general physical examination, it
was thought desirable to conduct a survey of
all our people with the aim of discovering any
unknown cases of infection. A rapid-fire tech-
nique has been worked out for these surveys,
and so arrangements were made for the New
York City team to come to West Street and the
State Department of Health’s team to visit the

four New Jersey locations. Results in the two
states were not significantly different.

For the Laboratories as a whole, 5,795 em-
ployees were available for testing, and of them
98.5 per cent were actually X-rayed. The find-
ings indicated that a few should have further
study, and they were photographed on our
regular machine. Only two cases of active
tuberculosis were found, an incidence of 0.035
per cent, as compared with the general Bell
System rate of 0.12 per cent and a rate of 1.5
per cent found in many industrial groups.

As a check on the survey, the few known
cases of arrested tuberculosis were included.
All were identified and reported. While they
will always carry the scars of healed lesions,
they are no menace to their associates, and
they have a normal expectancy of life.

All in all, we are members of about as
healthy a group as can be found, at least from
the standpoint of pulmonary tuberculosis.

The world’s largest open-cut copper mine,
located in Bingham Canyon, near Salt Lake
City, is using the mobile telephone to facilitate
operations of its electric ore-carrying and main-
tenance trains. The private mobile system
furnished by The Mountain States Telephone
and Telegraph Company for the Kennecott
Copper Corporation consists of four land sta-

the A T & T’s “Tele-
phone Screen Review” se-
ries. “Talk Jury” tells how
listening tests made by the
Transmission Standards
laboratory keep watch on
the quality of the many
varieties of talking circuits
used in the Bell System.
Laboratories’ people who
served on the jury were:
Marguerite Hutchinson,
Christine Scanlan, Esther
Rentrop, Claire Ohl, L.
Pinter, and J. L. Doncourt

tions, and mobile telephone equipment in-
stalled in six electric locomotives, two rail
“speeders,” and in the mine superintendent's
automobile.

Another private mobile system is being pro-
vided for Kennecott’s railroad which takes ore
from the mines to the Garfield and Magna
mills, some 15 miles to the north, on the south
shore of Great Salt Lake. Seven low-powered
land stations and 16 mobile units are included
in the project.

S. O. Morgan and A. N. Holden sailed for
England on April 2, where they are attending
an international conference of the Faraday
Society on crystal growth. Mr. Holden will
present a paper on methods developed in the
Laboratories. Later, Messrs. Morgan and
Holden will visit several laboratories in Eng-
land and on the continent to discuss matters
of interest in the crystal and dielectric fields.
They will return on May 26.

J. H. Felker is instructing forty-six students
at Whippany in the first term of Course 236 on
Electronic Circuits; the remaining two terms
of the course will be presented in the fall of
1949 and the spring of 1950. The course is the
first in the Out-of-Hour series to be given at
Whippany since the end of World War II.

J. A. Morton, in his
home town, Detroit,
addresses telephone
people and their
guests, the local sec-
tions of A.I.E.E. and
I.R.E., on the Tran-
sistor. Mr. Morton
was introduced by
E. C. Balch, chief
engineer of Michi-
gan Bell

R. O. Grisdale and his group in Transmission
Apparatus Development have moved from
Building 1D and 1E at Murray Hill. Mr.
Grisdale will be in 2C-271 and the group in
2B-301, 302, 303 and 308. D. R. Brobst and
his group have moved to 2D-428 and 460.

N. Y. Priessman and his group in Electronics
Apparatus Development have moved to their
new quarters at Murray Hill. Mr. Priessman
will be in 2A-324 and the others on the same
floor in 2A and 2B.

J. P. Guerard has moved from West Street
to 1A-158 at Murray Hill. C. M. Hebbert has
moved to 2C-375.

R. E. Ressler has transferred to Filler De-
velopment and is located in Room 2C-137.

Mysterious radar reflections which have
baflled the world’s electronics experts both
during and since the war have been explained
by scientists of Bell Telephone Laboratories.
The cause: flying insects.

Nicknamed “angels,” the heretofore unex-
plained “blips” have shown up confusingly
on many radar scopes as sharp echoes of short
duration, observable most frequently below
heights of 3,000 feet.

The explanation that the “angels” are caused
by flying insects is contained in a communi-
cation to the April issue of the Proceedings of
the Institute of Radio Engineers from A. B.
Crawford of Radio Research. The strange re-
flections were discovered during the war by
M. W. Baldwin, Jr., of Television Research.

Since that time, they have been the subject
of considerable research. A number of ob-
servers have suggested they were due to

atmospheric changes which result in turbulent
motion in the lower atmosphere.

The tests and observations reported were
sponsored jointly by the Laboratories and the
Naval Electronics Laboratory and were con-
ducted at Gila Bend, Arizona. Working on the
problem, besides Mr. Crawford, were L. R.
Lowry and S. E. Reed of Radio Research, and
J. B. Smyth and L. J. Anderson, of the Naval
Electronics Laboratory.

Mr. Crawford’s investigation of “angels” was
undertaken as part of fundamental studies of
microwaves which are being increasingly used
to carry telephone messages and television pro-
grams over the Nation’s communications net-

On one of his numerous trips to Detroit in connec-
tion with the 81-C-1 Teletypewriter Switching Sys-
tem for General Motors, W. M. Bacon was photo-
graphed with Fred Rogers, TWX engineer of the
Michigan Bell

In his communication, Mr. Crawford wrote
that he was led to the conclusion that the
reflections were caused by insects “when all
attempts to synthesize ‘angels’ by artificially
producing boundaries of temperature, humidity
or turbulence failed completely and when
visual observations of insects coincided strik-
ingly with the radar observations.”

In their attempts to synthesize the strange
patterns on the radar scopes, the scientists
exploded a small charge of nitro-starch in the
air, 500 feet above their radar antennas. They
flew a plane low over the radar and looked for
reflections from the exhaust gases. They built
bonfires, upwind, so that the hot combustion

To Union College, where he graduated in 1915,
journeyed H. J. Delchamps to represent the Labora-
tories in a series of interviews with members of the
senior class. With him in the recruiting party were
representatives of Western Electric, Long Lines, and
New York Telephone. Mr. Delchamps has recently
become president of Union’s Northern New Jersey
Alumni Association

gases and steam clouds formed by pouring
water on heated rocks billowed into the beam.
In all these experiments, the phenomenon was
never observable.

Later, working at night, they threw out a
strong searchlight beam, and stationed observ-
ers at different levels of a 200-foot tower.
While the observers counted insects, the radar
operators counted the appearance of “angels”
on their scopes. For example, in one fifteen-
minute period, twenty were counted, fifteen
coinciding with the sighting of an insect.

Mr. Crawford points out that insects fit most
of the descriptions which have been applied
to the mysterious reflections on radar scopes.
They are small, they move at a speed compar-
able to wind velocity, sometimes with and
sometimes against the wind, they are present
both day and night, and there are more of them
in warm weather than in cold.

News Notes
O. E. BuckLey attended the Mid-Century
Convocation and Inauguration of President
Killian at the Massachusetts Institute of Tech-
nology early in April. He was a guest at an
official reception for Winston Churchill.

Durinc Marcu, M. J. KeLty spent a week at
the Los Alamos Laboratory of the Atomic En-
ergy Commission, New Mexico, and later vis-
ited the Northwestern Bell Telephone Com-
pany, where he talked to management and
engineering groups. Dr. Kelly spoke on The

Position of Universities With Respect to Indus-
trial Research at the Symposium on Coépera-
tive Engineering, conducted by the Institute
of Technology of the University of Minnesota,
with the codperation of the Minnesota Branch
of the American Society of Engineering Edu-
cation and interested industries, through the
Center for Continuation Study. He also went
to Washington in connection with Research
and Development Board activities.

A. B. Ciark visited Atlanta on March 2 and 8,
where he talked to Southern Bell supervisory
people on Laboratories Developments.

W. H. Martin talked to the Deal-Holmdel
Colloquium on March 18 about the develop-
ment of the new combined telephone set.

HARVEY FLETCHER attended the meeting of
the Governing Board of the American Institute
of Physics. As a member of the Advisory
Board of the Research Council, he visited Rut-
gers University on March 16. Dr. Fletcher has
been elected to Honorary Membership in the
Acoustical Society of America.

W. FonpmL_er was guest of honor at the first
annual dinner of the American Technion So-
ciety, Philadelphia Chapter, on March 19.

C. S. Demarest has transferred from Patent
and has been appointed Apparatus Consultant,
reporting to W. H. Martin.

L. P. JoHNson witnessed the installation at
Troy of No. 5 crossbar systems in that city.

G. W. Gruman, G. D. Epwarps, E. F. Wart-
son, and E. G. D. Paterson discussed tele-
typewriter development and quality assurance
matters with the Teletype Corporation in
Chicago in February. During the same month
Mr. Gilman, Mr. Edwards and Mr. Watson
also visited Detroit in connection with operation
of teletypewriter switching systems in that area.

W. M. Bacon, W. Y. Lance and M. N.
SMALLEY visited the Teletype Corporation in
Chicago for conferences on new teletypewriter
apparatus. Mr. Bacon also conferred in Detroit
on the 81-C-1 switching system in service for
the General Motors Corporation.

T. L. Corwin analyzed certain teletypewriter
troubles at Philadelphia’s accounting center.

R. Marino interviewed the Primary Examiner
at the Patent Office on a patent application.

G. T. Morris attended a hearing before the
United States Court of Customs and Patent
Appeals in Washington in various interfer-
ence proceedings.

D. W. PuILiion was at the Patent Office dur-
ing March relative to patent matters.

Recent retirements from the Laboratories in-
clude W. C. Kiesel and Frank Waldman with
40 years of service; E. H. Goldsmith, 35 years;
and H. M. Trueblood, 31 years.

During H. M. Trueblood’s 31 years of serv-
ice with the Bell System, he has been inti-
mately associated with the development of
methods and procedures for the protection of
telephone service, plant, and personnel from
the effects of induction from power and elec-
trified railway circuits. For the past ten years,
as Protection Development Director, he has
also been in charge of development work on
protection from lightning and from corrosion
damage to cables. He has been a member and
secretary, since its organization, of the Joint
Subcommittee on Development and Research
of the Edison Electric Institute (formerly the
National Electric Light Association) and the
Bell System. This committee has published sev-
eral volumes of reports that have been of fun-
damental importance in the codrdination of
paralleling telephone and power circuits for
the avoidance of interference. In the railway
electrification field, Dr. Trueblood has been
concerned with the Pennsylvania, New Haven,
Norfolk and Western, Virginian, Lackawanna
and other electrifications from the standpoint
of preventing inductive interference with com-
munication circuits. In the fields of his profes-
sional interests, he has been active as co-
author of several papers.

During the war, Dr. Trueblood directed
work on cathode-ray oscilloscopes of various
types for use in the development, manufacture
and field testing of radar systems.* He was
also conerrned with the development of radar
indicators, and with other war assignments. At

the end of the war, he returned to the work
on electrolysis prevention and protection with
which he had previously been concerned.

Dr. Trueblood received B.S. degrees from
Earlham College and Haverford College; spent
five years as field officer with the U. S. Coast
and Geodetic Survey; attended M.I.T. and
then Harvard, from which he received his
Ph.D. in physics; and was instructor and then
assistant professor in the Electrical Engineer-
ing Department of the University of Pennsyl-
vania. He joined the Engineering Department
of the A T & T in 1917 and a few months
later went to the U. S. Naval Experimenta!
Station at New London in research work in
connection with submarine detection. He re-
turned to the A T & T in 1919, becoming a
member of the D & R and came to the Labo-
ratories during the 1934 consolidation. Since
1947, he has served as Chairman of the Pro-
gram Committee of the Laboratories’ commu-
nications development training for new mem-
bers of the technical staff.

Dr. Trueblood is a Fellow of the A.LE.E.
and a member of its Board of Examiners; a
Fellow of the A.A.A.S. and of the Acoustical
Society, and a member of the American Physi-
cal Society. He is a director of the National
Association of Corrosion Engineers and Chair-
man of its Policy and Planning Committee. He
is a member of Sigma Xi.

Since the practice of patent law not only in-
volves knowledge of the law but also requires
a grasp of technical matters, members of the
Patent Staff all have a technical background
and some of them have practiced engineering.
One of the latter was W. C. Kiesel who, be-
fore entering our Patent Department in 1917,
had graduated from the University of Ken-
tucky (B.M.E., 1908; E.E., 1911), had then
done equipment engineering for Western Elec-
tric, and had been chief engineer of Western’s
affiliated company in Vienna, Austria. When
the United States’ entry into World War I was
imminent, Mr. Kiesel returned, but soon went
back to Europe, where he served as a first
lieutenant in the 307th Field Signal Battalion,
and participated in the St. Mihiel and Argonne
drives.

That war over, Mr. Kiesel took up patent
work, because he liked the opportunity it af-
forded for individual effort and the exercise of
the imagination insofar as foreseeing trends
of development was concerned. His first work
was on manual circuits and later on dial cir-

cuits and equipment. In 1925 he became a
supervisor, and had charge of substation appa-
ratus, vacuum tubes, microphones, and loud-
speaking devices for reproducing sound. In
1936, outside plant matters were added, and
in 1945 switchboard and submarine cables.
During World War II, he also handled anten-
nas and anti-submarine devices.

Having been admitted to the bar after night
study in New York Law School, Mr. Kiesel’s
civic interest led him to become a judge of a
minor court in his home town of Florham Park,
N. J. For a number of years, he was a member
of the Zoning Board there. Once a breeder and
exhibitor of dogs, he is still a judge for the
American Kennel Club; so that he is doubly
entitled to his friends’ greeting, “Good morn-
ing, Judge!”

In World War I, Elsworth Goldsmith went
to France as a master signal electrician. When
active service was denied him in World War
II, he did the next best thing—he returned to
the Laboratories for war work.

After graduation from Yale in 1910, he
worked for General Electric at Lynn for a
year, then at the suggestion of his friend, J. N.
Reynolds, he came to Western Electric to help
design panel apparatus. With that background,
he transferred in 1916 to New York Telephone,
where he became an equipment engineer.
From then until 1938, he was the Telephone
Company’s representative in connection with
the engineering work of every central office in
New York as “panel” spread over the city.
Then for four years he was concerned with
fundamental plans; and for another four years
in the Laboratories he wrote instruction man-
uals and instructed military teaching personnel
on radar, gun directors, bomb computers,
depth charges and submarine detectors. That
task completed, he transferred to Patent,
where he has been preparing applications on
various subjects, including automatic message
accounting systems.

Since Mr. Goldsmith’s two hobbies—sailing
and the collection and repair of antique
watches—can be practiced hereabouts, he ex-
pects to remain in New York.

In a little shop in Building T, a milling ma-
chine is learning the ways of a new master.
Unlike its neighbors, the lathe and the drill
press, it is strictly a one-man machine, for
Frank Waldman carried the key in his pocket
right up to April 8, when he retired.

Mr. Waldman was born in Czechoslovakia
and came to this country with some experience
as a machinist. He entered the Western Elec-
tric shop at West Street in 1906, worked else-
where for three years, returned during World
War I and has been one of us ever since. One
of his early jobs was on printing telegraph
equipment; he built the power rectifier for the
long-wave transatlantic radio station at Rocky

>. T. Lewis run Theodor Olsen T. W. Mackey
W. H. Long M. B. Long J. M. Acker D. T. Osgood P. F. McGann
J. T. O’Lea L. T. Anderson E. L.O Albert Rodel
35 years H. L. Bowman ert
Eugene Peterson Patrick Col R. E. Ressler Frank Schuler
F. H. Graham Leonard Vieth R. A. Sykes W. C. Sturzenegger
R. H. Miller J. F. Wentz E. B. Destler G. W. Turner Elena Tighe
: David Westbrook H. S. Wertz
90 T. A. Durkin 1. Week
95 Ludwig Fichter CSY 10
J. L. Agterberg 0 years F. G. Fossetta 9. Yeutter years |
F. G. Colbath C. E. Fordham O. R. Garfield 5 W. O. Baker
P. B. Fairlamb L. W. Giles William Gulker 15 years Ethel Blocker :
R. H. Galt W. F. Kannenberg Ernest Guzmich Daniel Breen L. W. Lott :
F. J. Given W. D. Mischler W. L. Hardardt Franklin Dermond Lorraine Moss
J. L. Hysko N. C. Youngstrom Francis McConville C. R. Hornby Mary Roberts
May 1949 193

Point; helped set up WEAF on the eleventh
floor at West Street; the television radio trans-
mitter at Whippany in 1927 and the sound-
picture equipment in Section L. For the last
three years he has been a laboratory mechanic
in Electronics Development, working princi-
pally on tube parts and waveguides. Along
with. those jobs, he is guide, counsellor and
friend to the engineers on all sorts of mechani-
cal problems.

Mr. Waldman expects to occupy his leisure
with work around his house and garden near
Port Washington, or perhaps to get a job in
some nearby machine shop.

R. E. PooLe was appointed an A.J.E.E. repre-
sentative to American Standards Association
Sectional Committee C16 on Radio as a re-
placement for W. Wilson, deceased.

A. G. JENSEN has been appointed chairman of
the Institute of Radio Engineers Television
Systems Committee, and vice-chairman of the
Institute’s Standards Committee as of May 1.

B. S. Biccs is chairman-elect of the High Poly-
mer Group of the North Jersey Section of the
American Chemical Society.

L. H. Germer has been appointed to the
A.1.E.E. Subcommittee on the Electrical Prop-
erties of Gases.

A. Menpizza has been appointed chairman of
a special committee to study accelerated tests
for supplementary finishes for zinc, A.S.T.M.
Committee B-8, Subcommittee V.

C. E. SHANNON appeared on the televised ra-
dio program We, the People on March 22,
participating in the discussion of some aspects
of electronic computers.

AMONG THOSE who attended the American
Physical Society meeting in Cleveland were
W. P. Mason, A. J. AHEARN, K. G. McKay,
G. H. Wannier, R. M. Bozortn, F. S.
GoucuER, J. M. RicHARDSON and W. SHOCKLEY.

K. K. Darrow visited Cleveland from March
9 to 12, where he spoke before the Lambda
Club of Case Institute of Technology on Mag-
netic Resonance and the American Physical
Society on Linguistics of Solid State Physics.
B. McMILLAN gave the second lecture entitled
Characteristics of Information in a series of six,
and C. E. SHANNON the fourth entitled Com-
munication in the Presence of Noise, in a course
on Recent Developments in the Theory of
Communication given by the A.I.E.E. Commu-
nication Division in New York, jointly with the’
New York Section I.R.E.

Younger members of the Laboratories and their friends generously supported a party and dance
sponsored by the Hospital Visiting Committee of the Legion Bell Telephone Post No. 497 to
obtain funds for airfoam cushions for veterans’ wheelchairs. Included in the group below are,
standing: J. Smith, his wife, Helen,* E. Strubing,* Gloria Ryan,* Claire King, S. Robertson,
Anne Pfeiffer,* Jane Nichol and J. P. Larimer;* seated: Carman Abascal, C. W. Peterson,*
Clotilda Abascal,* F. X. Sullivan,* Nancy Nelson,* C. Dalm,* Dorathy Sherry,* J. A. Ceonzo,*

the New York Society of Model Engineers. H. H.
Hagens (above, left), director of the show, looks
over a live steamer, which took three years of spare
time to build. Folks at Murray Hill brought the

The Model Railroad Club, which has yet to
celebrate its first birthday, exhibited the crafts-
manship of its members at West Street in early
March to thousands who visited the Audito-
rium not once but several times to enjoy its
displays. Then, under the director of the show,
H. H. Hagens, the entire set-up moved to Mur-
ray Hill and later to Whippany. Heart of the
show was a portable HO layout, borrowed
from the New York Society of Model Engi-
neers and operated during the hours the show
was open with equipment entered by club
members. Trains varied in size from HO
gauge cranes made to scale while in the Pacific
from a tin can by Paul Mallery, chairman of
the club, to a giant live steam model locomo-
tive which C. Karthaeuser helped to make.
Many steamers entered were made from
scraps; others from modelcraft kits. Posters on
display everywhere showed such things as the
technique of building various models, the pop-
ularity of various gauges. The accompanying
photographs tell a graphic story of interest in
the show.

J. R. Townsenp spoke on Materials in the
Modern World before the Pueblo and Denver,
Colorado, Chapters of the American Society
for Metals on March 17 and 18, respectively,
and The Mountain States Company.

A. W. Treprow and M. D. RicTerink dis-
cussed porcelain enamel problems the
Ingram-Richardson Manufacturing Company,
Beaver Falls, Pennsylvania.

J. B. DeCoste conferred at the National Lead
Company Laboratories in Brooklyn on stabiliz-
ers for polyvinyl plastics.

C. V. LunpBERG at the Tonawanda Plant wit-
nessed a demonstration of the use of high-
frequency heating equipment in conjunction
with the extrusion of plastic jackets on cable.

May 9 Yale Glee Club
May 16 Ezio Pinza and Mary Martin
May 23 Bidu Saydo
May 30 Polyna Stoska
June 6 Lee Fairfax

J. H. Scarr presented a paper on The Metal-
lurgy of Germanium and Silicon Semi-Conduc-
tors at the L.R.E. Semi-Conductor Symposium
held in New York in March. He also gave a
talk on Transistors to the Metropolitan Section
of the American Chemical Society.

V. T. Waiver and A. L. RicHEyY went to
Miami to discuss alpeth cable performance.
L. E. Assorr attended a conference on non-
destructive testing at the White Oak Labora-
tories of the Naval Research Laboratory at
Silver Springs, Maryland.

C. L. Luke visited the National Bureau of
Standards in Washington recently.

L. A. Wooren served as chairman of the
March 25 afternoon session of the Symposium
on Specific Methods of Analysis, sponsored by
the New York Academy of Sciences, Section of
Physics and Chemistry, at which W. E. Camp-
BELL delivered a paper on the Electrolytic
Analysis of Tarnish Film on Metals.

F. J. Prachnaik of the Carpenter Shop watches closely
as Mary Routhier hammers according to instruction
during the Household Repair Course given by the
Buildings Shops supervisors to women Pioneers

K. G. Cout.Lee and D. B. HERRMANN attended
a conference at Wright-Patterson Airfield, Day-
ton, at which insulating materials used in AN
connectors were discussed.

in the Bell Telephone Laboratories to the
Metropolitan Microchemical Society.

G. T. KoHMAN participated in the radio broad-
cast of Headlines in Chemistry, sponsored by
the American Chemical Society. Synthetic
Quartz Crystals was the topic of discussion.

Going for a ride to Whippany, this one-ton
cable termination house was rigged with a
boom and lowered intact down the side of
Building T to the truck below. The house,
4 x 8 x 8, had been used by the Transmission
group in connection with development work
on Type K-2 carrier systems. It is now being
used by the Plant Department at Whippany
for storage of equipment

In Cuicaco, A.S.T.M. spring group meetings
were attended by J. Crasrrer, G. N. Vacca,
C. C. Hipxins, W. J. Kiernan, W. J. Puarr,
W. Basincton, I. V. Wittiams, A. MENDIZzzA,
H. Peters and G. R. Goun.

E. I. GREEN gave a talk on Frequency Divi-
sion Multiplexing in the Bell System before the
U. S. Air Force Institute of Technology on
April 6 at Wright Field, Dayton.

R. J. Puiviers witnessed high impact shock
tests on submarine projects at Anacostia.

The Laboratories and the community of
Fairlawn, New Jersey, lost a valued citizen in
the death of Mr. Carlton. A Canadian by birth,
he was raised in New Hampshire and entered
Dartmouth in the class of 1923. In 1925 he
became a member of the Technical Staff of
the Laboratories and in 1931 moved to Rad-
burn, New Jersey, where for the past eighteen
years he had been in the forefront of every
progressive and constructive movement in the
Borough of Fairlawn.

Mr. Carlton’s early work at the Laboratories
was concerned with the electrical design of
radio transmission equipment for airplane ap-
plication, both civil and military. Later he be-
came concerned with the mechanical design of
that equipment. For a short time he transferred
to the network group, but with the advent of
war, he was assigned to the radar field, where
he was engaged in the development of equip-
ment of both airborne and naval application.
In 1945 he transferred to telephone work in
the microwave range. Mr. Carlton had a spe-
cial talent for careful design of waveguide
components and intricate electromechanical as-
semblies and, during work on the New York-
Boston radio-relay project, he was responsible
for the equipment design of the microwave
amplifier for the Western Electric 402 tube. He
also carried out the equipment design for the
transmitting amplifier and modulator for the
New York-Chicago system, the project he was
engaged in at the time he died.

Having served as a Radio Operator in World
War I, Mr. Carlton became one of the found-
ers of the Dartmouth Radio Club while at col-
lege, and in later years organized the Fair-
lawn Boys’ Club and instructed its Radio Club
for more than a decade. He was also active in
church work and in scouting, having served

for several years as scoutmaster and later as
District Commissioner of the North Bergen
County Council. A memorial fund in his mem-
ory was established for the Fairlawn Boys’
Club to enable his community and his friends
at the Laboratories to perpetuate his memory
in the work that was closest to his heart.

In 1933, Mr. Wagner retired from the Lab-
oratories, bringing to a close a long career of
skilled tool, die and model making for various
branches of the Bell System, the latter years
in the Tube Shop in Building T. Following his
retirement, Mr. Wagner moved to Hollywood,
California, to be with his son and daughter.
He enjoyed fifteen and a half years of leisure
and was in excellent health until the end.

Durinc THE I.R.E. National Convention in
New York in March, the following papers
were presented: A General Review of Linear
Varying Parameters and Nonlinear Circuit
Analysis, by W. R. BENNETT; Antenna Systems
for Multichannel Mobile Telephone, by W.
C. Bascock and W. Nytunp; An Impulse
Generator-Electronic Switch for Visual Testing
of Wide Band Networks, by T. R. Fincu; Pro-
gramming of a Computer for Playing Chess,
by C. E. SHANNON; Propagation Variations at
VHF and UHF, by K. Butiinctron; A Test
of 450-MC Urban-Area Transmission to a Mo-
bile Receiver, by A. J. Aikens and L. Y. Lacy;
Echoes in Transmission at 450-MC From Land
to Car Radio Units, by W. R. Younc and L. Y.
Lacy; Television by Pulse-Code Modulation,
by W. M. Goopa..; A High-Efficiency Sweep
Circuit, by B. M. Ortver; A Six-Channel Ur-
ban Mobile System With 60-KC Spacing, by
R. C. SHaw, P. V. Dimockx, W. Strack and
W. C. Hunter; Aspects of Double-Stream Am-
plifiers, by J. R. Prerce, W. B. HEBENSTREIT
and A. V. HoLt_tenserc; The Metallurgy of
Germanium and Silicon Semiconductors, by
J. H. Scarr; Physics of Rectification and
Transistor Action, by W. H. Brattain; and
Reactance-Tube Modulation of Phase-Shift
Oscillators, by F. R. Dennis and E. P. Fevcn.

A.S.T.M. Committee meetings in Washington
were attended by R. Burns, J. D. Cummincs,
G. Derc, A. H. Fark, J. J. Martin, E. E.
Wricut, G. R. Goun, J. P. Guerarp, K. G.
Cout Ler, D. B. HERRMANN, C. L. Luke and
H. A. Birpsatt. During the meetings, I. L.
Hopkins spoke on Biaxial Stresses in Poly-
ethylene and W. O. Baker on Dynamic Rhe-
ology of Polymers.

SEVERAL DIFFERENT PLANTS of Western Elec-
tric were visited by members of the Laborato-
ries recently. At Haverhill, J. W. McRae, E. I.
GREEN, F. J. Given and R. M. C. GrREENIDGE
discussed the manufacturing processes for
transformers, coils and resistors. At Allentown,
N. Y. PriessMAN, G. T. KouMan, C. J. Froscu,
C. B. Green, J. A. MILLer and G. K. TEAL
discussed thermistors; J. P. MESSANA, glass seal
terminals; and E. B. Woop, N. INnstey, L. L.
Locxrow and T. L. TANNER, equalizer prob-
lems. At Burlington, W. L. BLack examined
tool-made sample of the 22E speech input
equipment. At Winston-Salem, H. A. Frep-
ERICK and A. C. KELLER discussed vibrating
reed selectors; J. E. Corpin, airborne equip-
ment; and C. W. RAMspDEN, pulser networks.
At St. Paul, V. F. Bouman attended a Quality
Survey on step-by-step switches. Mr. Bohman
also visited the Hawthorne plant, where he
discussed various problems relating to step-by-
step apparatus.

During a spring concert given at noon in the
restaurant, the Whippany Men’s Glee Club,
under the direction of B. J. Thomas, with the
bass viol, gave out with a few hillbilly num-
bers just for fun. Vocalist for the occasion was
M. H. Gilson with his ukulele at the micro-
phone, assisted by F. F. Gruber and F. E. De-
Motte, guitarists, and W. H. Thatcher, accor-
dionist of the Club

L. L. Spangenberg (below), the accompanist
in the Whippany Men’s Glee Club, was photo-
graphed playing a piano solo during a portion
of the program

W. J. Kine attended the meeting at Wright
Field, Dayton, of the Committee on Pulse Ca-
bles of ANRFCCC.

A. W. Westling of the L. M. Ericsson Com-
pany, Stockholm, and H. J. B. Nevitt of the
New York office of that company visited Mur-
ray Hill recently.

Muriel Warren of the Building Department
is sailing for Naples on May 26 to sing in
operatic performances in Italy and to consider
the offer of the Roman Cinema Company to
sing in its productions. Professionally known as
Dea Lovati, Miss Warren has studied the
piano since she was nine and voice since she
was thirteen, when she came to New York to
be taught by masters from Italy. A lyric-colora-
tura, she made her debut at eighteen as Gilda
in Rigoletto in the Young Stars Grand Opera
Company and after that sang with the New
York Civic Grand Opera, the Monte Carlo and

D. G. BLatrner and J. H. WappDELL visited
the Eastman Kodak Company and Wallensak
Optical Company in Rochester in connection
with industrial cameras.

C. R. Tarr and H. A. Baxter participated in
conferences on the coérdination of subcontrac-
tors’ designs of submarine projects at General
Mills, Minneapolis.

H. L. Roster has completed a month’s assign-
ment at the Naval Air Test Center, Patuxent
River, Maryland, where he assisted Navy per-
sonnel in the tests of aircraft radio equipment.

W. J. KieRNAN attended a course on Appear-
ance Measurement at the Henry A. Gardner
Laboratory in Bethesda, Maryland. He also at-
tended recent sessions of the Optical Society
of America in New York.

A. C. WALKER discussed construction of steel
bombs for growing quartz crystals at the
Watertown Arsenal, Massachusetts. He also
discussed quartz crystals with members of the
Department of Geology of Harvard University.

A. G. Ganz visited Carnegie Institute at Pitts-
burgh, and the University of Chicago and
Northwestern University during the week be-
ginning March 7 to interview prospective em-
ployees. He also visited the Hawthorne Works
in connection with magnetic problems.

R. A. Sykes attended a committee meeting of
the Research and Development Board sub-
panel on frequency control devices at the
Georgia Institute of Technology.

New York, who have
evinced a fine in-
terest in the art.
The instructor, Irma
Rothstein, standing,
assisting girls at a
table, left to right:
Pat Caruso, Eliza-
beth Bates and Dor-

tive of Portland, Oregon, Miss Warren came
to work at the Laboratories during the war.

News Notes
J. W. Smrirn, F. E. Nimmcke and J. B. D’AL-
BORA Observed performance tests of fire con-
trol equipment at Syracuse.

G. D. JoHnson, A. A. Lunpstrom, R. W.
Sears, R. G. STEPHENSON and P. H. THAYER
made visits to several organizations such as
Massachusetts Institute of Technology, the Bu-
reau of Standards, Moore School of Engineer-
ing and the Naval Research Laboratory, where
they discussed computers.

Aside from how you look, you are taking a
risk when you are too fat or too thin. For the
overweights there is a greater chance of high
blood pressure, strained heart and kidneys, a
higher incidence of diabetes and gall bladder
trouble. Underweights tire quickly, become
easy victims of nervous disorders and diseases,
such as tuberculosis, resulting from under-par

Food Groups
For simplicity, you may divide the food fac-
tors into the following groups:

for building muscles and re-
conditions. And, of course, there is the matter pairing body tissues that wear
of looks—vital to women, especially in the out daily
summer, and of some importance, even to Vitami d

So check your weight in the table below oa ; ,
and if it’s out of line, start working on it now. ki
workings
If You Are Overweight Fats and
Exercise will help take off some poundage, Carbohydrates . . for energy

but ignoring hunger pangs will bring quicker
results. Remember that appetite is a habit
pattern, and often a faulty guide to the foods
your body needs. Since authorities agree that
most excess fat problems are caused by too
much eating and drinking, try to curb your
appetite.

It is strange, yet true, that the same foods
recommended for overweights—but in different
proportions—can be used to add extra pounds
by those whose weight is too low. To stimu-

All of these food factors are necessary, but
the fat and carbohydrate group can be in-
creased or decreased according to your energy
needs. (You still get some calories for energy
from fats and carbohydrates present in sup-

[Editor's note—Miss Neasham graduated
from New York University in 1947 after
specializing in nutrition. The table at the bot-
tom of this page was taken from Metropolitan
Life’s booklet, Overweight and Underweight.
Suggestions for future articles on health will
be welcomed. |

These tables are based on numerous Medico-Actuarial studies of hundreds
of thousands of insured men and women.

Height Height
(with Small Medium Large (with Small Medium Large
shoes on) Frame Frame Frame shoes on) Frame Frame Frame
Feet Inches Feet Inches

plementary amounts in the other groups.) The
principal sources of proteins, vitamins, min-
erals, fats and carbohydrates are to be found
in the foods listed below. These foods should
be the backbone of a daily diet for the over-
weight and underweight, as well as for the

To insure a good appetite for the foods you
need, go easy on hard and soft drinks, cakes,
cookies and crackers, pies and pastries, candy
and chocolate, sugar and other sweets. They
supply mainly calories. And calories alone, even
for the underweight, will not put curves and

The Principal Sources of Proteins, Vitamins, Minerals, Fats and Carbohydrates

GIVE Your Body Notes for
FOODS
Mainly Also Normal Weights Overweights Underweights
Meat Proteins Vitamins Adults need one to | Lean pieces only. Take extra portions
Poultry B Complex two portions a day. | No oily fish. for body building.
Fish A from Liver Cooking and prepa-
Eggs Minerals ration without butter,
Dried Beans Iron fats and oils.
Dried Peas
Milk Proteins Other To help meet a | Avoid sweet and sour | Use cream as well as
Cheese Mineral Minerals grown-up’s daily | cream, as well as ice | whole milk. Mix
Calcium and calcium require- | cream. Use skim | powdered whole
Other Vitamins Vitamins ments: 3 glasses of | milk, buttermilk, cot- | milk into milk and
Milk- (D if added | milk or its equiva- | tagecheese;and make | other foods. Eat
Containing B, to milk) lent in other foods; | up for their lack of | whole-milk cheeses.
Foods e.g. 3 glasses of | vitamin A by eating
milkapproxi- | moredark green leafy
mately equals 1% | and yellow vegeta-
pound of cheese. bles, also apricots.
Citrus Fruits Vitamin Vitamin At least one gener- | Unsweetened citrus | Sweetened if de-
or A from ous serving. fruit or juice. sired.
Tomatoes Tomatoes
Fruits in Vitamins Mineral One other a day | Select fruits (un- | Eat fruits for be-
Addition to Minerals Iron from recommended. sweetened) for des- | tween-meal snacks.
Citrus Dried Fruits serts.
Vegetables — Minerals Vitamin A Two big helpings | No oil on salads. All the butter, sauces
Especially Vitamins from or more. No butter or fat on | and dressings you
Dark Green Dark Green vegetables. want.
Leafy and Leafy and No cream sauce, Hol-
Deep Yellow Yellow landaise or mayon-
Vegetables naise.
Potatoes Carbohy- Vitamin One serving. Not more than 1 | More than 1 por-
drates small potato, with no | tion, with butter, fat
Minerals butter, fat or cheese. | or cheese.
Vitamin
Whole Grain or | Carbohy- Vitamin 2-4 slices of bread | Only 2 slices a day. As much as you like.
Enriched Breads drates B, a day or equivalent
and Cereals in whole grain
cereals.
Butter, or Oleo- | Fats Vitamin 2 tablespoonfuls | Each tablespoonful | Add as much as you

P. B. Drake visited the Teletype Corporation
to discuss questions in connection with the
production of readers and perforators for the
AMA system.

At THE HawTHoRNE plant in Chicago, C. C.
BARBER and M. Fritts discussed new designs
of crossbar switch; A. C. GiLMorE, equipment
units for common systems; C. C. HipkIns,
W. J. Kiernan and R. J. PHam, general fin-
ishes; W. BABINGTON and I. V. WILLIAMS, raw
materials; E. T. BALL, cost production studies
for No. 5 crossbar equipment; W. E. Grutz-
NER, testing equipment for No. 5 crossbar sys-
tem; H. N. Wacar and E. G. Watsu, produc-
tion of UB relays; J. W. McRae, H. A. Frep-
ERICK, J. J. Kunn, A. C. Ke.xer, H. O. Siec-
MUND, R. C. Davis, B. F. Runyon and H. M.
Knapp, crossbar switch and wire spring relay
problems; T. A. MARSHALL, the automatic mes-
sage accounting system; R. R. STEvENS and
C. E. MircuHELL, granular carbon for the trans-
mitter unit in the 500-type set; W. L. Turr-
NELL and L. Vietu, the manufacture of the
new telephone set, and coin collector prob-
lems; A. C. EkvALL, components for the new
subscriber set; V. T. WALLDER, polyethylene on
alpeth cable; and L. W. Gites, at Hawthorne
and Haverhill, problems relating to economic
studies of the manufacture of old apparatus.

P. H. Smirx conferred on the design of sub-
marine projects at the Bureau of Ships, the
Navy Department and the Naval Research
Laboratory in Washington.

J. D. Sarros participated in a symposium on
Navy equipment at the Naval Research Lab-
oratory in Washington.

R. C. Newuouse, R. F. Lane, F. C. Warp
and E. A. BESCHERER visited Watson Labora-
tories in connection with procurement of radio-
telephone equipment for the U.S.A.F.

S. C. Hicur spoke on Naval Air Defense Prob-
lems before the Volunteer Ordnance Division
W1 at the Bureau of Ordnance in Washington.

K. O. Tuorp, R. V. LouHmiLLer and P. F.
RECKENZAUN of Manufacturing Relations, Bur-
lington, were visitors in Whippany during
March, and H. C. Brear.ey, also of Burling-
ton, during the first week of April.

J. N. Suive gave demonstration lectures on
Transistors before I.R.E.-A.LLE.E. groups in
Washington and Baltimore. He also addressed
the Physics Colloquium at Johns Hopkins Uni-
versity on the same subject.

T. C. Fry, O. Myers and C. E. Brooks visited
the Pacific coast during the month of March,
stopping at Los Angeles, San Francisco, Seattle
and Portland.

G. A. Hurst, A. A. Mayer, D. H. PENNOYER
and F. F. Sarp.ey discussed switching matters
with the Michigan Bell Telephone Company
people in Detroit.

H. M. Spicer conferred on motor-driven auto-
transformer designs with the Superior Electric
Company at Bristol, Connecticut. He also dis-
cussed engine control equipment designs with
the Duplex Truck Company at Lansing.

R. D. de Kay observed a new type ringing
interrupter at the plant of the Stromberg-
Carlson Company in Rochester. He also ob-
served the new power plant for the 7A2 system
built by Federal Radio and Telephone Com-
pany for the Rochester Telephone Company.

L. S. C. Nees discussed new designs for ther-
mal operated relays with the Struthers Dunn
Company at Philadelphia.

M. A. Froperc studied the effect of variable
power service upon the rectifier inverters in the
L carrier station at Knoxville, Alabama.

H. T. LANGABEER visited the St. Louis office
in connection with the 301C power plant.

A. E. Gersore and R. V. BRUCKMANN were in
Media in connection with the Laboratories’
trial of reed keyset equipment and Class AR
changes in the AMA central office equipment.

G. H. DuHNkRACK made a study in the new
No. 5 crossbar central office, Vineland, New
Jersey, of the application of Plant training ma-
terial to central office maintenance.

At Pornt BREEZE, D. G. BLatTTNer, J. F.
BaLpwin and R. A. Hecnr discussed the
manufacture of manual apparatus; F. S. Kam-
MERER, central office cords; C. A. WEBBER and
H. H. SraresBner, cord development; D. T.
EIGHMEY, cording problems in connection with
the new station telephone set; and G. H. WiL-
LIAMS, JR., switchboard plugs.

W. R. GoEHNER was at the Audichron Com-
pany in Atlanta regarding the application of
standard Western Electric audio facilities to
special announcing systems.

R. A. Miter and L. B. Cooke attended two
meetings of the Radio Manufacturers’ Associa-
tion, TR-10, Audio Facilities Committee. They
also attended a RMA Committee meeting on
AM broadcast transmitters. Mr. Miller and
H. W. Aucustapr participated in a joint meet-
ing of the newly formed committees of the
Audio Techniques, Video Techniques and

F. A. Coes attended conferences on magnetic
tape recorder-reproducers in Chicago at the
Magnecord Company.

J. M. Ducumw and V. T. CALLAHAN observed
the first pilot model of the new automatic
diesel engine set at the General Motors plant
in Detroit. Mr. Callahan also visited several
K carrier stations in the vicinity of Toledo.

H. J. Berka discussed, with the Crouse-Hinds
Company at Syracuse, problems in connection
with air navigation obstruction lighting and its
control for the TD-2 microwave equipment.
He also visited St. Louis with R. H. Tweedy
of the O & E to confer with the Southwestern
Bell and the Daybrite Manufacturing Company
on central office lighting problems.

G. E. Dustin conferred at Scranton with local
telephone engineers on method of dressing
four-wire solderless connectors in step-by-step
offices.

K. M. Ferzer and J. G. Fercuson, while at
Albany and Baltimore, made studies of No. 5
crossbar equipment after which they visited
Hawthorne to discuss with Western engineers
installation schedules for this equipment.

A. B. Ciark, H. H. Lowry, T. C. Fry, W. A.
MacNairr and A. J. Buscu inspected a No. 5
crossbar office at Vineland, New Jersey.

L. A. WEBER’s visit to Madison and Milwaukee
concerned the trial of the N signaling system.

THe LABORATORIES were represented in inter-
ference proceedings at the Patent Office by F.
Mour before the Primary Examiner.

In the facing advertisement, Rae MacEvoy
is shown in the free-space room at Murray Hill.
The sounds she hears are transmitted from an
adjacent room where F. M. Wiener (above)
is seen watching message registers as they
record her judgments. Transmission of the test
sounds is automatically controlled by the per-
forated tape shown in the foreground.

*Betty Anderson—Edward Hayward
*Carmela Arfuso—Dominick Liantonio
Ann Frustaci—*Frank B. Catalanello
Joan Gilmartin—*Gregory W. Fiederowicz
*Jean Grusha—John Gaydos
Betty Jane Harrison—*Philip E. Hogin
Ann Iapalucci—Frank L. Bonasia
Elizabeth Kradell—*Charles J. Mataka
*Virginia Lent—DeWitt C. Gedney
*Jean McDonald—*J. A. Ceonzo
‘Kristine Mortensen—Harold C. Hotaling
*Catherine Roth—William E. Potter

Elizabeth Uptegrove—*Warren E. Mathews
*Members of the Laboratories. Notices of engage-

ments and weddings should be given to Mrs. Helen
McLoughlin, Room 803C, 14th St., Extension 296.

The Murray Hill Chorus has extended a cor-
dial invitation to all Laboratories’ personnel,
their families, and friends to attend its annual
Spring Concert on Tuesday evening, May 24,
at 8:30 p.m., in the Summit, New Jersey, High
School Auditorium. Their program will include
a wide variety of selections, Negro spirituals,
a Russian liturgical chant, a sea chantey, and
several semi-popular numbers. L. A. Meacham,
playing the violin, will be accompanied by
the Chorus in his own arrangement of an
Andante by von Diffendorf. Further informa-
tion about tickets will be announced later.

In addition to this performance, the Chorus
plans to present selected parts of the program
at the Veterans’ Hospital in Lyons, New Jersey,
on Sunday evening, May 15. Daniel Kautz-
man, Summit High School music director, will
conduct both performances, and Miss Capitola
Dickerson, of Summit, will be the accompanist.

E. C. Molina was a guest speaker at the
Quality Control Conference held at Georgia
Institute of Technology on March 25 under the
auspices of the Georgia Section of the America
Society for Quality Control and the Atlanta
Chapter of the Society for the Advancement of
Management.—The Atlanta Journal.

A number of letters have been received in
Publication from Stanley Watkins, who re-
tired last fall and is living in Kent, England.
In one letter he says:

“The sunsets are unbelievable. In the house
we are occupying temporarily, we see them
to full advantage as we look across a wide field
(young onions) to the sea, which is prevented
from invading us by chalk cliffs about 40 feet
high. The fact that behind these sunsets there
is a naval base or something, which indulges
in spasmodic gun practice at odd moments,
doesn’t detract too much from their beauty.
This is a little corner of the realm which re-
joices in maximum sunshine, minimum rain,
and practically no fog.

“Living far enough from any large town to
be beyond the commuting belt to all intents
and purposes, the austerity annoyances are
almost non-existent. No queues or anything like
that. Things are very much better throughout
the country than they were a year ago. There
is still a great shortage of certain kinds of
material, notably, of course, building stuff and
the things we are exporting, such as anthracite,
but if one can overcome the irritation at not
being able to get just what he wants when he
wants it, life isn’t so bad.”

What happens when you hear? What happens
inside your ear when sound waves come in
from a telephone conversation?

Bell Telephone Laboratories scientists have
developed special apparatus to help answer
these questions, for the telephone system is
designed to meet the ear’s requirements for
good listening.

In the test pictured above, the young lady
sits before loudspeakers in a soundproofed
room with a small hollow tube, reaching just
inside the ear canal. Sounds differing slightly
in frequency and intensity come from a loud-
speaker. The subject seeks to tell one from
another, recording her judgment electrically
by pressing a switch.

Meanwhile, the same sound waves pass down
the hollow tube to a condenser microphone,
and a record is made of the exact sound intensi-
ties she identified. Results help reveal the
sound levels you can hear clearly and without
strain — the sounds your telephone must be
designed to carry.

Scientists at Bell Telephone Laboratories
make hundreds of tests in this manner. It’s
just one part of the work which goes on year
after year at the Laboratories to help keep Bell
System telephone service the finest on earth.

Exploring and inventing, devising and per-
fecting, for continued improvements and
economies in telephone service.

Bell Laboratories Record  1949-05: Vol 27 Iss 5