sistor” and designates a new
type of circuit element whose elec-
trical resistance varies rapidly with
change in temperature. In contrast
with metals which have small positive
temperature coefficients of resistance,
thermistors are made from a class of
materials known as semi-conductors
which have relatively large negative
coefficients.

The behavior of semi-conductors is
not a new phenomenon; in fact,
Michael Faraday, as early as 1834,
reported measurements on the ex-
tremely high negative temperature co-
efficient of resistance of silver sulphide.
Electric heating elements consisting
of a mixture of rare earth oxides were
developed by Nernst fifty years ago.
These early devices, however, were

not easily reproduced and did not have
constant characteristics or long life.

The specific resistance versus tem-
perature characteristics of three semi-
conducting materials are shown in
Figure 1. The upper curve is for
uranium oxide (U;0,) which has a
specific resistance of 50,000 ohm-cms
at o degrees Centigrade. The specific
resistance decreases rapidly with rise
in temperature, being 2,800 ohm-cms
at 100 degrees and 15 ohm-cms at
500 degrees Centigrade. The shape of
this curve is typical of a large number
of oxide semi-conductors. A mixture
of nickel oxide (NiO) and manganese
oxide (Mn.O;) shown in the next lower
curve has a still larger negative tem-
perature coefficient of resistance, the
specific resistance values at 0 and 500
degrees Centigrade being respectively
10,000 and o.8 ohm-cms. Silver sul-

phide (AgsS),;exhibits a linear rela-
tionship between the logarithm of the
specific resistance and the tempera-
ture below 179 degrees Centigrade. At
this temperature a change in crystal
structure occurs which decreases its
specific resistance by a factor of about
vo and thereafter with increasing
temperature the coefficient is slightly
positive. The curve for platinum is
plotted for comparison purposes; its
temperature coefficient has a small
positive value and the specific resist-
ance is low, around 10° ohm-cms.

There are three common ways of
using thermistors in electric circuits.
In the first or externally heated
method, the resistance of the ther-
mistor is controlled by the ambient
temperature. The second or directly
heated method allows the electric cur-
rent in the circuit to pass directly
through the thermistor, thus heating
it and changing the impedance in the
circuit. The third or indirectly heated
‘method uses a thermistor

The resistance versus power char-
acteristics of a typical Western Elec-
tric 1A thermistor which is made of
uranium oxide are shown in Figure 2.
This is a static curve since for each
point sufficient time is allowed so that
the resistance attains its steady value.
At room temperature and low power
the resistance is 78,000 ohms. An in-
crease in power, however, heats the
unit and lowers its resistance until at
ten milliwatts the value is approxi-
mately 30,000 ohms and at 100 milli-
watts only 400 ohms.

The static voltage versus current
curve for this same thermistor is
shown by the solid curve in Figure 3.
At low current where Ohm’s law is
obeyed the plot is a straight line, hav-
ing a slope of forty-five degrees. As
the current is increased, however, the
slope decreases until at about one
milliampere the voltage reaches a

6
having aseparateheating
coil placed in a control- os} “XY
ling circuit; the heat gen- Pa
erated in it regulates the , '° i" URANIUM
thermistor resistance. © 93
Thermistors suitable for = ~w
102
each of these three cir- % a —
cuit uses are shown in ¢ 10 oo
the headpi A _ 63 MANGANESE
=
bient temperature-con-
trolled thermistor is sec- 2 107!
SILVER
ond from the right. The 2 “s SULPHIDE
10
two units at the left are «
directly heated devices. 10
The ‘one enclosed in the
tube with PLATINUM
metal electrodes at either 10-5 L—
end is a Completed West-
ern Electric. 1A thermis- -50 0 50 100 150 200 250 306° 350 400 450 500/
TEMPERATURE IN DEGREES CENTIGRADE
tor, while the other is the -
internal structure of the Fig. 1—Resistance versus temperature characteristics

maximum and thereafter decreases as
the current is increased. The falling
portion of the curve, therefore,
exhibits a negative resistance charac-
teristic. At currents beyond 100 milli-
amperes the voltage drop in the
semi-conductor as shown by the dotted

Fig. 2—Resistance versus power charac-
teristic of directly heated thermistor

line c has become so small that it is
the same order of magnitude as the
voltage drop in the metal lead wires,
indicated by the dotted line p. The
solid curve, which is the sum of these
two voltages, thus has a second point
of inflection and its slope becomes
positive again. Although this curve is
extended to ten amperes for analysis
purposes, the 1A thermistor cannot
carry currents greater than fifteen
milliamperes continuously without

In order to determine the life of 1A
thermistors they have been placed in
a circuit where an off-and-on current
cycle of ten milliamperes a-c has been
repeated every thirty seconds over an
extended period of time. Resistance
measurements were made on the
units periodically in order to deter-
mine their stability with time. Figure
4 shows the results on a typical unit
whose initial resistance at 76 degrees
Fahrenheit is 62,000 ohms. The gen-
eral trend is a rise in resistance
during the first part of its life, after
which it becomes quite constant.
Over a period of fifteen months, dur-
ing which time the thermistor was
put through 650,000 heating cycles,
the cold resistance did not vary more
than seven per cent. The resistance of
the thermistor when hot was found
to be equally stable.

If a directly heated thermistor is
placed in series with a source of volt-
age, key, milliammeter, and protect-
ing resistance as shown in Figure 5,
the meter will show a delayed build-
ing-up of the current following closure
of the key due to the thermal capacity
of the thermistor. This delay is
illustrated by the current versus time
curve for a typical 1A thermistor. The
initial current, which is determined by
the cold resistance of the thermistor,
is small and rises slowly at first, then

pointed out that thermistors
made of silver sulphide or
uranium oxide are usable only

resistance. Nickel manganese 10-5
oxide does not polarize and is
therefore equally stable in
either a-c or d-c circuits.

more rapidly as the thermistor be- ohm heating coil is shown in Figure 6.
comes hot. The final current is With no current flowing the resistance
limited by the circuit resistance. The is one megohm, at ten milliamperes it
magnitude of the time delay amounts is 10,000 ohms, and at fourteen milli-
to about one-half second for the par- amperes the resistance is eight ohms.
ticular circuit conditions shown in The curve flattens at this point be-
Figure 5; it increases with decrease in cause of the change in crystal struc-
battery voltage. By a suitable design ture of the silver sulphide. The
of the thermistor and choice of cir- thermistor resistance thus changes by
cuits it is possible to vary this time a factor of 100,000 for a power dissi-
delay from a few milliseconds to pation of only twenty milliwatts. This
several seconds. This time-delay curve is completely reversible. In-
property of thermistors is a distinct directly heated units made of a mix-
advantage in many applications since ture of nickel and manganese oxides

it provides an action which if ob- have excellent life characteristics but
tained by other techniques

wh
more cumbersome and costly. 22 ee
Directly heated thermistors 52 4
capable of carrying much g&
larger currents than fifteen 3% of
milliamperes, the maximum £2
continuous current rating of “#_,

the 1A thermistor, have been 2 2 4
made by pressing semi-con-
ducting materials into discs in Fig. 4—Life characteristic of typical 1A thermistor
much the same way that
silicon carbide varistors are formed. do not cover such a wide resistance
These may also be made in the same__ range with small heater powers.
shape as the ambient temperature- The thermal and electrical charac-
controlled unit shown in the head-_ teristics of thermistors suggest a large
piece. Such thermistors have charac- number of circuit applications. One
teristics of the same form as the 1A obvious use for devices having such
but can carry currents of several high temperature coefficients of re-
amperes. Due to their large thermal sistance is that of a resistance ther-
capacity they have longer heating mometer. In this application the
and cooling periods when used as_ measuring current is kept so low that
time-delay devices. it produces no appreciable heating
The thermistors which have been and the thermistor resistance is de-
described have all been of the directly pendent only on the ambient tem-
heated variety. By placing a heating perature. At 25 degrees Centigrade
coil around the thermistor in such a_ the changes in resistance of uranium
way that it is insulated electrically oxide, nickel manganese oxide, and
but in contact thermally, an indirectly _ silver sulphide are respectively 3.0, 4.2
heated device is obtained. The ther- and 4.9 per cent per degree Centigrade
mistor resistance asa functionofheater change in temperature. This compares
current for a unit made of a silver with 0.35 per cent per degree Centi-
sulphide semi-conductor with a 100- grade for platinum. A second use for

thermistors is that of compensating
for changes in resistance due to
ambient temperature in circuits hav-
ing a positive temperature coefficient
of resistance. This is accomplished by
associating the thermistor with series
or parallel circuit elements so that the
change in resistance with temperature
of the combination is equal and op-
posite to that of the remainder of
the circuit which it is necessary to
compensate.

The resistance versus power char-
acteristics of thermistors make them
useful as sensitive current and power-
measuring devices. Due to the ex-
tremely small electrical capacity asso-
ciated with these devices they are
suitable for use in either low or ultra-
high-frequency circuits. When placed
in the proper bridge circuits thermis-
tors may be used as flow meters,
vacuum gauges, or to measure other
physical quantities dependent on the
flow of thermal energy from a hot
body. High-sensitivity bolometers for
the measurement of radiant energy

have been constructed using directly
heated thermistors for the tempera-
ture-sensitive element.

Thermistors may be used to stabi-
lize the output voltage in circuits in
which the input voltage varies over a
considerable range. As shown by the
voltage current plot in Figure 3, the
thermistor voltage decreases with in-
crease in current over the central
portion of the curve. If a suitable
chosen value of ohmic resistance is
placed in series with the thermistor,
the voltage across the combination
may be held practically constant in
this current range. The series combi-
nation of thermistor and resistance
will therefore act as a variable current
shunt if placed in parallel with the
load and will tend to maintain the
load voltage constant. Although
changes in temperature limit the ac-
curacy of regulation, these errors can
be kept to a minimum by operating
the thermistor at temperatures well
above ambient.

entire voice-frequency
range. The output
power is around one
milliwatt and, al-
though the character-

istics are not extremely stable, these
thermistors have been operating for
over two years in a continuous life
test circuit without serious signs of
deterioration.

A standard relay may be made
into a slow-acting device by putting a
directly heated thermistor in series
with its winding. The magnitude of
the delay depends on the thermistor
characteristics, the relay constants,
and the circuit conditions. False
operations of relays resulting from
high voltage surges may be prevented
in this manner. The thermal inertia
of the thermistor, together with its
high initial resistance, discriminates
against voltage surges of short dura-
tion, but an application of voltage of
greater duration, even though of
lesser magnitude than the surge volt-
age, operates the relay after a small
delay. This is the application for
which the 1A thermistor was designed
and a large number of these units have
already been installed in the telephone
plant, primarily in ringing circuits
for private-branch exchanges.

Indirectly heated thermistors may
be used as variable resistance devices
which are operated by an electric
current through the heating coil
rather than by a sliding contact as in
a standard rheostat. These devices

have the advantage that their resist-
ance change is continuously variable
and that they may be operated elec-
trically from a distant point. This

Fig. 6—Resistance versus heater-current
characteristic of an indirectly heated ther-
mistor which was made of silver sulphide

type of thermistor has found im-
portant applications in automatic
transmission-regulating networks.
Thermistors have already found im-
portant applications as circuit ele-
ments. As time goes on, further uses
will undoubtedly be found for these

or more sources when the quantities
are expressed in decibels. Examples
are finding the combined level of
several noise sources or integrating
the components of a complex tone.
These computations are time-con-
suming by ordinary methods, if there
are many components, and they are
subject to inherent errors due to mis-
placed decimal points. The labor-
saving devices described here have
been developed to obtain results more
quickly and to reduce errors when
many computations have to be made.
quantities involved in these
examples are usually expressed in db

with respect to a chosen reference
power Po by the formula db =10 logo
(P /Po). If the components combine on
a power basis, the resultant level in
db is determined by the sum of the
component powers. The mathematical
process, therefore, consists in finding
p/P, for each component, adding, and
reconverting to the db scale. Suppose
two components measure 53 db and
49 db above the reference level; then
by the above equation 53 db cor-
responds to a power ratio of 2 x 10%,
and 49 db to 8 x 104, or 0.8 x 10%. The
sum is 2.8 x 10°, which represents a
level of 54.5 db. This requires, be-
sides division and addition, the find-
ing of both logs and antilogs. Whether
the computations are done by log

tables or slide rule, it is time-consum-
ing and subject to error, particularly
if the components are numerous and
cover a wide range.

If two components are equal in
magnitude their combined level is
3 db higher than the components
whatever the original levels were. This
follows from a fundamental property
of the db scale; adding two equal
powers is equivalent to multiplying by
2, which represents a 3-db increase in
power. Similarly, adding two compo-
nents which differ by 3 db is equiva-
lent to multiplying the higher of the
two powers by 1.5, or adding 1.8 db
to the higher level, regardless of the
absolute levels. Thus for any two
components which combine on a
power basis, there exists a unique
increment which, added to the level
of the higher component, gives the
level of the combination. This incre-
ment is a function only of the

order the components are added:
When there are many components,
this process becomes tedious because
each succeeding component must be
subtracted from the progressive “sum”
to find the increment to be added.
This procedure can be mechanized
readily in several ways, by using
special slide rules. The one shown in
Figure 2 is the closest analogue of the
mathematical process just described.
It has special linear scales on an ordi-
nary 10-inch slide rule, and an indi-
cator capable of crosswise as well as
lengthwise motion. This indicator is
made of transparent material, and has
inscribed on it not only the usual
vertical index line, but also a straight
line inclined at 45 degrees, and a
curved line like that of Figure 1
plotted in appropriate units along the
vertical line. The origin is at the inter-
section of the two straight lines.

on it, is a convenient method
for combining two compo-
nents. When three or more
components are to be added,
the operation is performed
stepwise, by combining two
components and then the third with
the “‘sum,”* and similarly each addi-

*The word “sum” will hereafter mean the db
figure representing the level resulting from the
combination of two or more components whose
levels are also expressed in db.

Fig. 1—This curve shows the amount in db by which
the combined power level of two components exceeds

the higher of the two components to
be combined. By moving the trans-
parent indicator vertically the 45-
degree line can be made to intersect
this scale at a point corresponding to
the lower of the two components. The

increment will then be found added to
the higher component where the
curved line intersects this scale. For
example the components shown in the
photograph are 12 and 10, the incre-
ment is 2.1, and the “sum”’ is 14.1,
which is the final answer for these two
components. If other components are
to be added, the vertical line is
shifted to the “sum,” and the opera-
tion repeated for each component. To
avoid having to remember the “‘sum”’
while shifting the indicator, the arrow
index on the otherwise blank slide is
shifted to mark the “‘sum,” and the
vertical line is then shifted to the
arrow. Both plus and minus scales
have been provided to cover the com-
plete range.

numbered to correspond to the db
difference between the components to
be added. The indicator has been re-
moved from the array of broken lines
in Figure 3 to give a clear picture. If
the components are —20 and —30 the
glass indicator cross-hair is set at
—20, and the zero of the lower part
of the slide scale at —30, as shown.
The broken line labeled 10 would be
under the cross-hair, at its lower ex-
tremity. The cross-hair is then moved
to the right until it is set on the upper
extremity of the broken line num-
bered 10. The answer with the proper
increment added is the scale readin
under the cross-hair. This follows be-
cause the displacement of the upper
end of each broken line is equal to the
increment for the corresponding dif-
ference in level between the two com-
ponents to be added. The broken lines
to the left of zero on the slide are en-
graved in red instead of black and are
used when components are to be sub-
tracted instead of added.

Fig. 2—Special slide rule, for combining db levels, which embodies the curve of Figure 1
directly on the indicator. The indicator slides both horizontally and vertically

Fig. 3—Slide rule with the increments of Figure 1 shown by broken lines on the slide

many components which are equal in
magnitude. As set in Figure 3 a level
of 30 db on the lower scale under the
index 1 on the slide is the result of the
combination of 10 components each of
20 db, or 50 each of 13 db, etc.

A third device for adding the com-
ponents is shown in the headpiece. It
was designed by W. Koenig, Jr.,
specifically for computations of inte-
grated spectra, each of which involves
many components. The operator sets
an index on each component in turn.
The cumulative “‘sum”’ is available at
all times. This device is based on the
same principle as the others and is
illustrated in Figure 4, with the cover
removed. Two index lines are in-
scribed on a transparent disc of lucite;
the outer is a circle and the inner a
spiral. As seen through the window of
the cover, the spiral looks like a
slightly curved line which moves
along the scale when the disc is ro-
tated. By offsetting the center of the
spiral from the scale, the spiral always

which makes it much easier to set
accurately. The answer is read from
the scale beneath the index line at the
extreme right.

grasps the slide and moves it to the
left until a small point on the arm
above the slide strikes the edge of the
disc. This edge is shaped to cor-
respond to the curve of Figure 1.
Releasing the thumb lever first re-
leases the clutch, then allows the
arm to resume its normal position
against an adjustable back stop. The
travel of the arm is 3 db along the
scale when the spiral intersects the
circle, which corresponds to adding
two equal components. At the point
of maximum separation between the
circle and the spiral, which cor-
responds to about 18 db difference in
level between two components, the
arm almost touches the edge of the
disc and consequently permits only a
very small advance.

In using this device only that part
of the lucite disc at the right of the
shaft in Figure 4 is visible to the
operator, as shown in the headpiece.
The first component is set under the
index line at the right by moving the
slide through the apparatus by hand.
The second, and each subsequent
component, is set by turning the
lucite disc which moves the left index
line to the desired position on the
scale. Operating the thumb lever to
the limit of its motion after each set-

ting automatically moves the slide
by the appropriate increment. The
progressive “sum” then appears under
the index line at the operator’s right.
Operation is simplest when the largest
component of the series is set first but
thereafter they may be taken in any
order that is desired.

These models all have approxi-
mately the same accuracy—about 0.1
db. Components so far below the
cumulative sum that individually
they do not add an appreciable incre-
ment are neglected. If there is a large
number of these, the accuracy will be

improved by totalling the low compo-
nents separately and adding this sub-
total to the sub-total of the high
components.

These devices have been injuse for
about two years and have proved emi-
nently practical. They are known by
those who use them as “‘db adders.”
The particular scales shown in illus-
trating the several devices are those
which apply when the components
combine on a power basis. Similar
scales can be provided for other laws
such as those encountered with the
addition of current or voltage.

Fig. 4—Mechanized arrangement for adding db increments. The disc is shaped to
conform to Figure 1 and acts as a stop to the clutch which advances the slide

of a coil to increase its in-
ductance, it exacts a compensation in
energy for its contribution. This toll,
which is dissipated in the magnetic
material, is called core loss. The core
of a transformer in a power-trans-
mission system, for example, may be-
come hot to the touch, providing
tangible evidence of the dissipation of
energy. In fact a measurement of the
heat developed in such a core can be
used to determine the magnitude of
the core loss, commonly expressed in
watts per unit weight of the core ma-
terial. In the design of power appa-
ratus, the core loss must be limited to
prevent excessive waste of energy in
overheating.

In a high-quality inductance, such
as a loading coil or network coil used
in communication circuits, where the
energy levels are relatively very low,
the power dissipation due to core loss
is negligible so far as heating is con-
cerned. The effects of core loss on the
performance of these coils in trans-
mission circuits are of such im-
portance, however, that they govern
the practical application of ferro-
magnetic core materials. The meas-
urement and analysis of core loss
consequently assume
rdles in the development of ferro-
magnetic materials and the design of
high-quality coils employing them.

Instead of a direct measurement of
the heat developed in the core of a
high-quality coil, the increase in series

resistance due to core loss is deter-
mined from measurements on a-c
bridges equipped with vacuum-tube
amplifiers. The procedure is to meas-
ure the effective resistance R, and
subtract from it the winding resist-
ance. The difference is the core loss
resistance Ar. The winding resistance
consists of the direct-current resist-
ance Ry plus an alternating-current
resistance R, arising from eddy cur-
rents, dielectric loss, and distributed
capacity in the winding. This latter
resistance can be determined from
measurements on the winding without
the magnetic core. Figure 1 illustrates
schematically these various resist-
ances in series with the inductance.

Fig. 1—Core loss appears as one of the
components of the effective resistance of a
coil that has a magnetic core

The ratio of the inductive reactance
to the effective resistance is commonly
employed as a quality factor or figure
of merit of the coil, termed “‘g.”’ To
yield the highest value of “ Q” for a
given inductance, the core oe and
winding resistance must be made as
small as possible. A net gain in “Q”

realized from the use of a ferro-
magnetic core in place of a_non-
magnetic core when the ‘reduction in
winding resistance due to the smaller

number of turns required is greater
than the resistance added by core loss.

Core loss, or the amount of energy
dissipated, increases with both fre-
quency and the magnitude of the in-
duced flux. Hence, in a communica-
tion circuit, which has as its function
the faithful transmission of a current
of complex wave form, the core loss in
the magnetic material acts to modify
the shape of the transmitted wave and
reduce the fidelity. Its effects are to
attenuate the higher frequencies more
than the lower and to introduce non-
linear distortion. Since transmission
requirements on most network and
loading coils are severe ‘in these re-
spects, it is helpful not only to deter-
mine the total core loss, but to divide

Fig. 2—Wéith constant current, upper
graph, the relationship between Ar/pfi
and frequency is a straight line; and for
constant frequency, lower graph, the rela-
tionship between AR/pfi and flux density
is also a straight line for small values of

it into frequency and current’compo-
nents which can be related to the
operating characteristics of the coils.

Investigation has shown that the
total increase in resistance due to core
loss may be divided into three com-
ponents: one proportional to the
square of the frequency, one to the
product of frequency and the maxi-
mum flux density, and one to the first
power of the frequency. The first of
these components is called the eddy-
current-loss resistance, the second the
hysteresis-loss resistance, and the
third the “‘residual’-loss resistance.
An equation expressing them would
be written:

In these equations e, a, and ¢ are
eddy current, hysteresis, and “resid-
ual” coefficients of the core material
respectively, wu is the effective perme-
ability of the core, f is the frequency,
B,, the maximum flux density in the
core, and L the inductance of the coil.

The coefficients e, a, and c may be
evaluated by determining Ar from
a-c bridge measurements at two or
more frequencies at constant current,
and two or more currents at constant
frequency, and solving the set of
equations simultaneously. In practice
this solution is obtained graphically
as illustrated in Figures 2a and 2b.
When values of Ar /y/t are plotted for
the same value of current (or flux
density) at two or more frequencies, a
straight line may be drawn through
the points as shown in Figure 2a. The
slope of this line is “‘e,” and the ordi-
nate intercept is ¢+4Bm,. Similarly
when points are plotted for different
flux densities but at the same fre-
quency, the line shown in Figure 2b is
obtained. The slope of this line is

“a,” and the ordinate intercept is
c+ef. This determines both “‘e”’ and
“a,” and by substituting these values
into the expressions for the ordinate

Once these coefficients are known
for a given core structure, the core-
loss resistance can be calculated for
other currents and frequencies and
for other inductances by substituting
in Equation 1. Furthermore, a knowl-
edge of the relationship of these co-
efficients to the physical properties of
the core material and to the electrical
behavior of the coil is very helpful in
developing improved core materials
and in guiding their application.

The eddy-current coefficient ‘‘e’”’ is
an index to the energy dissipation
arising from currents induced in the
magnetic core material by variations
in the current through the coil wind-
ing. The eddy currents flow in planes
perpendicular to the paths of mag-
netic flux, and have magnitudes which
depend on the value and rate of vari-
ation of the magnetic flux and on the
resistance of the conducting paths
available to the currents. This re-
sistance is proportional to the resis-
tivity of the magnetic material and
the constriction of such paths. If the
core is laminated parallel to the paths
of the magnetic flux the eddy current
losses can be shown to be propor-
tional to the square of the lamination
thickness. If the core material is sub-
divided into small particles insulated
from each other, the eddy current
losses are proportional to the square
of the particle diameters. In high-
quality coils such as filter or network
coils, core rings made of insulated
and compressed magnetic powder are
commonly used because the eddy cur-
rents are minimized by the extremely
fine size of the particles. Overall losses
are limited by controlling the effective

permeability through proper adjust-
ment of the ratio of insulating and
magnetic materials. The determina-
tion of “ce” can be used in connection
with the development and manu-
facture of such cores to indicate the
uniformity of the various processes,
such as grinding or the application of

it
1916 1936
Fig. 3—Improvement in eddy current co-
efficient in cores used for voice-frequency
loading and retardation coils over the last
twenty-four years

the insulation, or to indicate the ef-
fects of systematically controlled
changes in these processes.

The hysteresis-loss coefficient ‘“‘a’’
depends upon’the composition of the
material and the heat treatment. Its
magnitude is controlled therefore by
selecting the most suitable material
and employing the most favorable
processing. The hysteresis loss is im-
portant not only because of its contri-
bution to the effective resistance of
the coil, but also as a source of distor-
tion of the wave form in the circuits
with which it is linked. This distortion
arises from harmonics and new fre-
quencies caused by the non-linear re-
lation between the magnetizing force

new frequencies may cause not only
distortion in the circuit containing the
magnetic material, but may produce
disturbances in adjoining channels of
multi-channel circuits. It has been
shown that these effects are propor-

tional to the product ays,,. The har-
monic distortion, or modulation, is
thus conveniently related to an in-
trinsic property of the magnetic
material, and the relatively simple de-
termination of the hysteresis coeffi-
cient “a”’ may be used in place of more
involved modulation measurements
for predicting and controlling this
effect of the magnetic core. As in the
case of the eddy current coefficient
“e,” a study of the change in the
hysteresis coefficient “a” with varia-
tions in manufacturing processes may
be used to determine directions for
improvement of the core material.
The “residual” loss term in Equa-
tion I is a result of the observation
that the total core loss as accurately
measured on a-c bridges is larger
than can be accounted for by the two
eddy current and hysteresis compo-
nents as conventionally determined.
This additional component has been
referred to also as “‘initial hysteresis”
and “‘magnetic viscosity.”’ Since the
increase in resistance of a coil due to
“residual” loss is a function of only
the first power of the frequency, is
independent of flux density, and does
not contribute to harmonic distortion,
it is not of as much consequence as the
eddy current and hysteresis losses.
Nevertheless it is desirable to keep the
residual constant ‘‘c’’ as low as prac-
ticable. The physical basis of residual
loss is still a matter of conjecture, but
- some control of the coefficient ‘‘c’’ is

obtained through proper choice of
composition and heat treatment of
the material.

The utility of core loss determina-
tions in development work and manu-
facturing control depends also upon
means available for rapid and ac-
curate measurements. As the quality
of the core is improved, the ratio of
core loss to the total effective resist-
ance measured on the bridge de-
creases, requiring greater precision of
measurement. Figure 3 presents, for
example, a picture of improvements
in the eddy current losses in cores used
in voice-frequency loading and net-
work coils during the past several
years. To provide high speed and ac-
curacy for the measurement of pres-
ent-day materials, a new bridge has
recently been designed and built and
described in a previous article.* In the
best quality cores, where highest
accuracies are required, the test coils
are prepared with a special stand-
ardized winding designed to minimize
the a-c winding losses. The coils are
thoroughly dried and then placed in
hermetically sealed containers for
measurement. The measuring equip-
ment is maintained in air-conditioned
rooms under practically constant con-
ditions of temperature and humidity.
Both alternating and direct-current
measurements are made on the same
circuit to avoid changing connections
or handling the coils.

This view of the new Bell Telephone Laboratories’ building at Murray Hill, New
Jersey, shows the general outline of the structure as it appeared on October 16. The main
entrance will be reached through the forecourt at the left in the structure connecting the
rear laboratory building with the chemical laboratories in the foreground. The one-story
structure at the right will contain the restaurant and cafeteria; directly above these and
connecting with the main building will be the clubrooms. The acoustical laboratory
and auditorium are not shown in this view but will be located slightly in front and to the
right of the restaurant. The heating plant is shown in the upper left-hand corner where
also will be located a garage and electric substation.

THE TWENTY-FIFTH anniversary of the
first successful transmission of speech across
the Atlantic by radio telephone was cele-
brated on October 21, 1940, when engineers
who accomplished the feat gathered at the
Laboratories. Since war conditions pre-
vented the reénactment of the original talk
to Paris, another of those early tests was
echoed by a telephone call from Dr. Jewett
to A. A. Scott, President of the Mutual Tele-
phone Company at Honolulu.

The radio telephone tests in which this
group of Bell System engineers participated
twenty-five years ago were a forerunner of
the transoceanic radio telephone service of
today, by which any telephone in the United
States can be connected to practically any
other telephone anywhere else in the world,

war conditions permitting. The transmitter
of twenty-five years ago was located at the
Arlington Radio Station where an antenna
was made available through the codperation
of the United States Navy. It was manned
by R. A. Heising, B. B. Webb and H. W.
Everitt. The listeners in Paris, H. E. Shreeve
and A. M. Curtis, had the use, at intervals,
of a radio antenna on the Eiffel Tower
through permission of the French Govern-
ment. At the same time Lloyd Espenschied
was stationed at the Naval Base at Pearl
Harbor, Hawaii; R. V. L. Hartley was at
San Francisco; William Wilson at San Diego;
and R. H. Wilson at Panama. O. E. Buckley
and H. Weinhart were concerned with
the production of vacuum tubes. B. W.
Kendall and C. R. Englund, after working
on apparatus design, monitored the trans-
mitter output at a receiver in New York.
John Mills was transmission engineer for the

Reunited at the Twenty-fifth Anniversary of Transatlantic Radio Telephony were: (Standing)

H. Weinhart, R. V. L. Hartley, C. R. Englund and H. W. Everitt; (Seated) F. B. Jewett,
H. E. Shreeve, B. B. Webb, L. Espenschied and E. H. Colpitts

Seldom does a physician receive the tribute of affection and gratitude which came to Dr. John
Slater Waterman at a dinner tended to him on October 23 on the occasion of his retirement.
The camera caught Dr. Waterman in the midst of this group of his friends

project. Speech transmitted from Arlington
was heard by all of these observers at various
times between August 26, 1915, and October
21; at Paris, which was the principal ob-
jective to be reached in the tests, the signals
received on October 21 were good enough
so that the French officers listening could
state that transoceanic radio telephony had
been accomplished.

Success of the tests was due to careful
planning and preparation. The project was
in general charge of Dr. Jewett and E. H.
Colpitts. Those present paid tribute to the
late General John J. Carty whose imagina-
tion and foresight were responsible for the
initiation of the project, and to the contribu-
tions of the late Dr. H. D. Arnold, who was
in direct charge of the research phases of
the subject.

After the completion of the Arlington
tests, the transmitter was dismantled and
the observers came home. The tests had
emphasized the need for larger tubes so as to
reduce to a workable number the 550 tubes
of 20 watts each in the final stage. Military
needs preoccupied the Laboratories for a
time, but in 1921 the invention of the copper-
to-glass seal made possible a 10,000-watt
tube. In the following year, work on trans-
atlantic telephony was renewed, using the
Radio Corporation’s large antenna at Rocky
Point, Long Island. Profit was taken of the
work which had meanwhile been done on
radio and carrier systems, and on January

15, 1923, a public demonstration was made
of transmission from New York to London.
So successful was this that the British Post
Office erected corresponding equipment.
Problems of interconnection of telephone
lines with radio were successfully solved, and
on January 7, 1927, transatlantic service
was opened for public use.

REDUCTIONS IN TELEPHONE toll rates from
points in New York City and vicinity to
certain points in Northern New Jersey com-
prising roughly the suburban area have been
announced by the New York Telephone
Company and the New Jersey Bell Tele-
phone Company.

Effective December first, the new rates
are a reduction of five cents from previous
rates. For example, on calls from Manhattan
south of 57th Street:

Locality New Rate Old Rate
Morsemere Io¢ 15¢
Elizabeth 15¢ 20¢
Montclair 15¢ 20¢
Orange 15¢ 20¢
Paterson 15¢ 20¢
Perth Amboy 20¢ 25¢
Rahway 20¢ 25¢
Summit 20¢ 25¢
Morristown 25¢ 30¢
Plainfield 25¢ 30¢
Dover 30¢ 35¢

A NEW TELEPHONE NUMBERING PLAN for
southern Westchester will become effective
with the issue of new telephone directories

Members of the Laboratories in the area
affected will receive from the New York
Telephone Company a booklet describing
the changes so that they may be in position
to answer questions from their neighbors
about the reasons for the change in central
office designations.

From NoveMBER II to 12 an early winter
storm of unusual severity, marked by tor-
nadoes, blizzards, and near-zero tempera-
tures, swept across the country from the
Rocky Mountains to the Appalachians doing

a course on frequency modulation conducted by
the Communication Group, AJI.E.E.

heavy damage to property over a wide area.
In some sections open-wire telephone lines
were hit hard. In the upper Mississippi
Valley the Madison-La Crosse-Hastings and
Davenport-Minneapolis routes suffered nu-
merous wire breaks.

In this emergency the new type-L carrier
system, on which installation and testing is
in progress between Minneapolis and Stevens
Point, was rushed into service, despite the
fact that regular commercial service is not
scheduled to begin until the middle of next
year. Fifteen Chicago-Minneapolis circuits
were routed over the coaxial between
November 11 and November 15. All of the
emergency circuits were restored to normal
routings as soon as the storm damage was
repaired.

K. K. Darrow spoke on The Ionosphere
at the October 21 meeting of the Colloquium.
The ionosphere is a region in the very high
atmosphere from which radio signals are
reflected, a fact which is adequately ex-
plained by assuming that region to be popu-
lated with free electrons. In exploring the
ionosphere, signals of a wide range of fre-
quencies are successively sent upward, and
the time elapsing before the return of the
echo is measured. The delay of the echo
multiplied by one-half the velocity of the
waves is called the virtual height of the
ceiling for the signal. Curves are then plotted
relating virtual height of ceiling to frequency
of signal. These curves are peculiar in shape
and vary remarkably with time of day,
time of year and epoch of the solar cycle.
By theory they can be translated into curves
relating electron-density to true height
above ground. The theory is approximative,
but the results are accurate enough to be of
value. The magnetic field of the earth affects
the observed values remarkably, making it
possible to test the theory and to evaluate
the field-strength at great heights. The free
electrons are supposed to be liberated from
the air-molecules by ionizing agents, of
which the chief but not the only one is
ultra-violet light from the sun.

At the November 4 meeting, G. R. Stibitz
lectured on Calculating With Telephone
Equipment. For years telephone relays have
benefited from numerical calculations per-

formed by telephone engi-
neers, and the time has
come to return the favor.
Telephone engineers are
now benefiting from nu-
merical calculations per-
formed by telephone
relays. A calculator com-
posed entirely of relays
and similar telephone and
teletypewriter equipment
has been constructed to
carry out the tedious com-
putations with complex
numbers which are needed
in the design of trans-
mission networks.

requirements for member-
ship. Any member of the
Laboratories is qualified if he either has pub-
lished original research in a recognized scien-
tific journal or is a member of at least one of
the following societies: the American Chemi-
cal Society, the American Mathematical
Society, or a member society of the Amer-
ican Institute of Physics. Anyone in the
Laboratories who is qualified to become a
member of the Colloquium may obtain an
application blank from Miss Kilpatrick on
Extension 484.

MetvitteE H. Manson, M.D., who be-
came Medical Director of the Laboratories
upon the retirement of Dr. J. S. Waterman,
is a graduate of the University of Minnesota
where he received his B.S. degree in 1926,
B.M. in 1928, M.D. in 1929, M.S. (Surgery)
in 1932 and Ph.D. (Surgery) in 1934. Fol-
lowing graduation from Medical School, Dr.
Manson served a year’s rotating interneship
at the University of Wisconsin General
Hospitals. From 1930 to 1933 he was a
teaching fellow in surgery at the University
of Minnesota Hospitals and from 1934 to
1937 served as an instructor in surgery in
these hospitals.

Early in 1937 he became a special repre-
sentative with the American College of Sur-

Dr. MEtvitte H. Manson
quiries regarding the recently appointed Medical Di- search and a fellow of the

geons in which capacity he
engaged in making a sur-
vey of the surgical train-
ing facilities in the United
States. Upon the comple-
tion of this work later
that year he accepted a
position with the Common-
wealth Fund as a medi-
cal executive in the hos-
pital division. He served in
an advisory capacity on
matters pertaining to the
establishment of hospital
facilities in communities.

Dr. Manson is a mem-
ber of Sigma Xi, Alpha
Omega Alpha, American
Society for Cancer Re-

American College of Sur-
geons. He has written a
number of papers that have been published
in scientific and medical journals.

Tue Menpuam property of the Labora-
tories, used for a number of years by the
Radio Development Department, is now on
the market for sale. The property has been
divided into three parcels: 25 acres, 49 acres
and 58 acres. The 49-acre parcel which in-
cludes a dwelling and garage has already
been sold. The larger of the two remaining
parcels includes an old frame house and the
laboratory building erected since the acqui-
sition of the property.

F. B. Jewett, as president of the National
Academy of Sciences, presided over the
autumn convention of the Academy, held
from October 28 to 30 in Philadelphia, and
spoke briefly at the dinner held on October
29. O. E. Buckley, Harvey Fletcher and
H. E. Ives attended various meetings during
the convention.

Dr. Buck ey has been appointed a mem-
ber of the committee on the John J. Carty
Fund of the National Academy of Sciences,
to serve until April, 1946.

H. S. SHEPPARD, at a Patent Department
luncheon held on October 30, spoke on
The License Contract. B. F. Stoddard made
the arrangements for the luncheon.

service have been granted to H. W. Schaefer,
165th Infantry, Fort McClelland, Annis-
ton, Alabama; W. K. St. Clair, Corps Area
Signal Office, Governors Island, New York;
D. L. Viemeister, United States Naval Re-
serve Radio School, Noroton, Connecticut;
and J. R. Sackman, Bureau of Ships, United
States Navy, Washington, D. C.

M. E. Srriesy, High Frequency Engineer
of the Transmission Development Depart-
ment, has been appointed Transmission En-
gineer of the Long Lines Department,
American Telephone and Telegraph Com-
pany. Since his transfer to the Laboratories
in 1929 from the Department of Develop-
ment and Research of the American Tele-
phone and Telegraph Company, Mr. Strieby
has been in charge of coaxial systems de-
velopment and has contributed largely to
its success.

J. F. Wentz, in charge of line engineering
and measurements under Mr. Strieby, suc-
ceeds him. Mr. Wentz was graduated by
Lehigh University in 1917 and entered the
Laboratories in 1919. His principal contri-
butions have been in the fields of loaded
submarine cables and more recently of
coaxial cables, particularly in the study of
transmission characteristics and the de-
velopment of methods of measurement.

Buckley, Mrs. Blackwell, William Wilson, H. Wilson (a guest),
A. B. Clark, Mrs. Clark, A. F. Dixon, and Mrs. Buckley

Steinberg and W. B. Snow visited the Clarke
School at Northampton, Massachusetts, to
inspect the present teaching methods using
group hearing aids.

AN ARTICLE ENTITLED Testing America’s
Ears, by F. L. Hunt, was published in the
October issue of the Bell System Quarterly.
Records of more than half a million indi-
vidual tests at the Bell System Exhibits of
the New York and San Francisco World’s
Fairs have provided the most extensive data
ever compiled for the study of hearing.

D. R. McCormack discussed and demon-
strated Centralized Transcribing by Tele-
phone before a conference of the American
Management Association held in New York
City on October 25.

G. C. Crawrorp of the Systems De-
velopment Department retired from active
service on the thirtieth of November, having
completed over thirty-two years of service
in the Engineering Department of the
Western Electric Company and the Labora-
tories. Mr. Crawford received the A.B.
degree from Harvard University in 1902
and the degrees of A.M. and S.B. in Elec-
trical Engineering in 1903 and 1904. In
1905, after a year teaching physics at the
University of North Carolina, he joined the
Engineering Department of the Western
Electric Company.

About this time Mr.
Crawford became as-
sociated with E. C.
Molina in a study of
the application of
probability to trunk-
ing problems. In the
course of this study
Mr. Molina sub-
mitted, for computa-
tion and reduction to
curve form, a formula
for the approximate
evaluation of the in-
complete binomial
expansion which in-
volved certain param-
eters m and p. Mr.
Crawford, in supervis-
ing this computation,
observed that as p be-
came small and, simul-

taneously, 7 became large,
it was not necessary to
know the values of both in
order to evaluate the bi-
nomial summation; it suf-
ficed to know only the value
of the product of and p.
This important fact was
called to the attention of
Mr. Molina with the result
that in 1908 he introduced
into the solution of trunk-
ing problems his Poisson
trunking formula.

In 1908 Mr. Crawford
left to instruct in physics
at the College of the City
of New York, but in Ig11
he returned to West Street
to engage in the development of ringing
systems, particularly the harmonic selective
ringing system. When the wartime engineer-
ing work was undertaken he took part in
the development of circuits and the prepa-
ration of bulletins covering the operation
and maintenance of radio equipment for
airplanes and submarine chasers.

Since 1922 Mr. Crawford has been con-
cerned with the development of repeaters,
and during this period was closely associated
with all of the work on the 22A1 (two-wire)
and 44A1 (four-wire) repeaters. Mr. Craw-
ford has also been connected with the de-
velopment of program circuits for broad-
casting systems since the beginning of this
work, particularly the 12-type and 14-type
amplifiers used in these circuits. Beginning
in 1928 he was associated with the develop-
ment of transmission measuring and control
circuits, such as the 1A amplifier-rectifier
that is used in the No. 8 test board and the
more recently developed 40B transmission-
measuring system.

For the three years previous to his retire-
ment the development of testing and main-
tenance switching methods for carrier and
coaxial repeaters was also included in his
work. He has rounded out his career by
supervising the development of a new tele-
phone repeater, the V-1, which is the most
substantial design improvement in voice-
frequency repeaters since the vacuum-tube
repeater was introduced into the telephone
plant over twenty years ago.

WITH OVER twenty-nine years of service
to his credit, G. W. Burchett of the Physical
Research Department retired on November
30. Before Mr. Burchett came to the Bell
System he spent several years in the
organizations of Hudson Maxim and Thomas
A. Edison. He joined the Special Apparatus
Department of the Western Electric manu-
facturing organization in 1911 and when
this was moved to Hawthorne he transferred
to the Model Shop. There he developed
special automatic machines for the manu-
facture of vacuum tube grids. During the
war he joined the printing telegraph group
where he assisted in the design and develop-
ment of various types of printing machines.

In 1921, Mr. Burchett entered one of the
Laboratories of the Physical Research De-
partment as an expert mechanic. One of his
first jobs was the development of the 540A W
loud-speaking telephone on which he re-
ceived a patent. Since then he has been
associated with the development of special
equipment and apparatus that is used by the
Physical Research group. He has also been
granted several patents for his work on the
artificial larynx.

W. A. MenuMe1 of the Finishing Shop of
the Plant Department is the man shown in
the Frontispiece on page 105.

K. K. Darrow spoke on October 17 be-
for the Physics Colloquium of M.I.T. on
Helium the Superfluid; on October 19 before
the New England section of the Physical

C—The stockroom which supplies materials to the
Building Shops is in charge of R. J. Hluboky

D—H. A. Kohler, a junior mechanic, cleaning
parts in the Finishing Shop as part of his
training in the Development Shop

Society on The Principle of Indefiniteness;
and on October 25 before Sigma Xi at
Smith College, Northampton, Massachu-
setts, on The Fission of Uranium.

R. M. Bozortu, on November 6, discussed
The Physical Basis of Ferromagnetism before
a science group of the Pittsfield plant of the
General Electric Company.

F.,S. GoucueEr, assisted by J. R. Haynes,
presented his lecture-demonstration, The
Microphone and Research, before the Science
Forum of the New York Electrical Society
on October 17. He also presented the same
talk before the Patent Society in Washing-
ton on November 7.

A CONFERENCE on Nuclear Physics held at
the Massachusetts Institute of Technology
was attended by K. K. Darrow, W. Shock-
ley, F. C. Nix and H. G. Wehe. A paper en-
titled Neutron Studies of Order in Iron-Nickel
Alloys by F. C. Nix and H. G. Beyer and
J. R. Dunning of Columbia Uni-
versity was presented by Dr. Nix.

Tue Metat Concress and tech-
nical sessions of the American
Society for Metals and the Ameri-
can Institute of Mining and
Metallurgical Engineers at Cleve-
land were attended by E. E.
Schumacher, W. C. Ellis and E. S.
Greiner. Mr. Ellis and Mr. Greiner
presented a paper entitled Egui-
librium Relations in the Solid State
of the Iron-Cobalt System. The
Metals Show, held in conjunction
with these meetings, was attended
by J. R. Townsend and C. H.
Greenall.

A. R. Kemp and F. S. Mat
visited the Packard Electric Di-
vision of General Motors Corpora-
tion at Warren, Ohio, to discuss
insulated wire problems. They also
discussed the same subject and
various rubber problems with en-
gineers of the Western Electric
Company at Hawthorne.

H. W. Hermance and T. F.
Ecan visited Pittsburgh, Wash-
ington and Baltimore to carry out
field analytical studies in connec-
tion with investigation of contact
performance in panel equipment.

C. J. Frosch, presented a paper entitled The
Dielectric Behavior of Some Polyesters at the
annual meeting of the Conference on Insu-
lation of the National Research Council.
The Conference met in Washington on
October 31 and November 1 and 2. G. T.
Kohman, D. A. McLean, E. J. Murphy,
H. A. Sauer, M. D. Rigterink and S. O.
Morgan also attended this conference.

R. M. Burns and H. E. Harine attended
a meeting of the Electrochemical Society
held in Ottawa.

IN A HALF-COLUMN ARTICLE in the Boston
Transcript for October 28, R. M. Foster dis-
cussed the probabilities of the order in which
numbers of the recent Selective Service draft
would be drawn.

H. A. Brrpsatt attended a convention of
the American Association of Textile Chem-
ists and Colorists that was held in New York
City on the eighteenth of October.

Radio Receiver that has since been installed at La
Guardia Field. H. B. Fischer is on the right

AMONG THE EDUCATIONAL
organizations that have un-
dertaken programs of par-
ticipation in the defense
program, the activities of the
mathematicians have espe-
cial significance in that the
applications of mathematics
are of basic importance both
in constructing and in oper-
ating the machines used in
present-day mechanized war-
fare. T. C. Fry has been
appointed a consultant to a
joint committee of the Amer-
ican Mathematical Society
and the Mathematical Asso-
ciation of America which
will carry on education and
research in those aspects of mathematics
that aid in preparation for war.

R. S. DecKER received an Honors Award
at Newark College of Engineering for being
among the first four in scholastic rating in
his class.

L. B. Eames completed twenty-five years
of service on November 29. He joined the
Building and Maintenance Department of
the Western Electric Company in 1915 as a
stock clerk. Two and a half years later he

transferred to the Purchasing
Department as a buyer of
hardware. Early in 1918 he
entered military service and
for slightly over a year was
in France with the 2nd Pio-
neer Infantry.

After the war Mr. Eames
returned to the Purchasing
Department. In 1921 he
went to the Apparatus De-
velopment Department as a
service clerk and a few years
later became supervisor in
charge of al] types of services
for engineers. When the Out-
side Plant Development De-
partment came to West
Street from the Maltz build-
ing, services for this Department were
transferred to Mr. Eames’ group. His
responsibilities cover the codrdination of
relations of the engineers with the Pur-
chasing Department and the Western Elec-
tric order-service department and includes
obtaining materials from stockrooms, fur-
nishing porter service, issuing orders on the
various development and plant shops, and
the shipment of apparatus and equipment.
In 1939 when service groups were reorgan-
ized and certain of their functions trans-

Puitip CurRAN
of the Plant Department com-
pleted thirty years of service
in the Bell System on the
second of November

W. J. Cuppy
of the General Accounting
Department completed forty
years of service in the Bell
System on November 2

J. C. Fretp
of the Switching Apparatus
Development Department
completed thirty-five years of
service on November 6

ferred to the General Serv-
ice Department, Mr. Eames
continued his responsibili-
ties in the local service group
of this Department.

Section of the American
Physical Society on the
subject The Coronaviser.
This meeting of the Metro-
politan section was held in
the Columbia Broadcasting
Studios in New York City
on November 15.

PRIOR TO THE OPENING of
a new coastal-harbor radio
telephone station, H. B.
Coxhead spent some time at
Tampa, Florida, and its
vicinity making tests and

L. B. Stark
of the Switching Development
Department completed thirty-
five years of service in the
Bell System on November 13

J. M. Fincu
of the Chemical Laboratories
completed thirty years of
service in the Bell System on
November 28

this type of service. Regular telephone
service through the Tampa station was
begun on November 1.

A PAPER PREPARED by W. R. Goehner on
A New Mirror Light Modulator was pre-
sented at the fall Convention of the Society
of Motion Picture Engineers held in Holly-
wood on October 22.

DuRING THE MONTH of November the
following members of the Laboratories
completed twenty years of service in the
Bell System:

Miss May T. Brown J. W. McCaw
Purchasing Department Plant Department
G. O. Pedersen William Wynn

J. F. Morrison spoke on Frequency Mod-
ulation Transmitters before the Communi-
cation Group of the A.I.E.E. New York
section on November 4.

E. S. SavacE visited Eau Claire, Wiscon-
sin, to inspect the coaxial cable and repeater
stations along the Minneapolis-Stevens
Point installation. Later he also visited the
main repeater station at Baldwin, Wisconsin.

W. A. Biscuorr attended a meeting of the
Technical Drawing Associates, held in Pitts-
burgh on October 3 and 4.

S. J. Harazim visited the Specialty Prod-
ucts Shop at Kearny to discuss changes in
the 19-C oscillator.

E. B. WHEELER and J. H. Bower at-
tended a committee meeting of the American
Standards Association on October 1 and 2
at the National Bureau of Standards in
Washington. The meeting was devoted to
the revision of the standards specifications
for dry batteries.

H. H. Sraesner visited Point Breeze on
October 7, and C. A. Webber and R. T.
Staples on October 16, to discuss cord de-
velopment problems.

W. V. Tuompson discussed problems of
the new vacuum tube audiphone cords at
Point Breeze on October 25.

H. H. Gienn and E. B. Woop, at Kearny
on October 17, discussed questions in con-
nection with wire development.

At THE HawTuorne plant of the Western
Electric Company H. A. Frederick, H. O.
Siegmund and J. J. Kuhn discussed relay
and switching apparatus problems; T. S.
Huxham, the manufacture of molded hous-
ings for the combined telephone set; D. H.
Gleason, crossbar switches; C. G. McCor-
mick, development of step-by-step banks;

Mr. McCormick also attended a Quality
Survey devoted to this subject; H. W.
Heimbach, problems involved in the manu-
facture of panel apparatus; R. J. Phair, sur-
face finish problems and the standardization
of new finish testing equipment; F. W. Trep-
tow, wiring problems connected with auto-
matic ticketing; and C. S. Fuller, enameled
wire and molding plastics. Mr. Fuller also
presented a lecture before the Western Elec-
tric evening school on the subject Thread-
Forming Plastics.

R. G. Wat inc visited Albany with L. W.
Williams of the A. T. & T. to discuss switch-
ing apparatus maintenance questions.

AT THE GENERAL Eectric Company in
Schenectady, C. H. Greenall, L. N. Hamp-
ton and I. V. Williams consulted with engi-
neers on metallurgical problems related to
electrically heated soldering coppers.

Joun R. Carson, research consultant in
the Mathematical Research Department, died
on October 31 at his home in New Hope,
Pennsylvania. Dr. Carson was graduated
by Princeton University in 1907, and re-
ceived a degree in electrical engineering in
1909. After two years with the Westinghouse
Electric and Manufacturing Company, he
taught at Princeton for two years. In 1914,
he entered the American Telephone and
Telegraph Company where he took part in
the first Bell System radio telephone de-

velopments. For a time he
was a member of the Patent
Department; returning to the
Department of Development
and Research, he transferred
with it to the Laboratories in
March, 1934.

One of the outstanding ad-
vances in the communications
art was Dr. Carson’s invention
of the single sideband carrier-
suppression system of carrier
current operation. This sys-
tem is in use on all long-wave
and some short-wave radio
circuits, and in wire-carrier
circuits of the Bell System
and of foreign countries. In
recognition the Institute of
Radio Engineers awarded him in 1924 the
Morris Liebmann Memorial Prize.

While twenty-five patents on specific in-
ventions stand in Dr. Carson’s name, his
most important work was in the application
of mathematical theory to transmission
problems, most of which require the use of
differential equations. By a happy inspira-
tion, Heaviside had suggested certain sim-
plifications in the arduous process of solving
these equations. Dr. Carson proved that
the simplifications were sound, and syste-
matized that “operational calculus” so that
it has become a useful tool for the network
engineer. His book Electric Circuit Theory
and the Operational Calculus is a classic in
this field.

Among the subjects which Dr. Carson
studied mathematically was the effect of the
current in one wire on the effective imped-
ance of its mate by forcing a non-uniform
distribution of the current. He also investi-
gated theoretically the effect of the earth on
the impedance of long conductors. He also
was active in the theoretical study of wave-
guide transmission.

Dr. Carson held the degree of Master of
Science from Princeton; he was a member of
Phi Beta Kappa, the American Mathe-
matical Society and the Institute of Radio
Engineers; and a fellow of the American
Institute of Electrical Engineers and of the
Royal Society of Arts in London. In 1936, he
received the honorary Doctor of Science
degree from Brooklyn Polytechnic Insti-

Medal of The Franklin Institute “in con-
sideration of outstanding contributions to
the art of electrical communication.”

H. T. Pu tis, with continuous service with
the Western Electric Company and the Lab-
oratories from 1921, died on the twenty-fifth
of October. Mr. Pulis had been a group su-
pervisor in the General Service Department.
Before joining the Engineering Department
of the Western Electric Company he had
worked for the Marine Engine and Machine
Company in 1904 and 1905, for the New
York City Railways from 1905 to 1907 and
for the Underwood Typewriter Company
from 1907 to 1921. With the Underwood
company he became an expert typewriter
repairman and came to West Street in this
capacity. Mr. Pulis had charge of this work
until 1937 when he became supervisor, re-
sponsible for mail, messenger, telegraph and
typewriter — services.

Joun a a group supervisor in the
General Service Department with over
twenty-three years of service in the Western
Electric Company and the Laboratories,
died on November 3. From 1908 to 1917 Mr.
McEvoy worked as a stock clerk for
McQuillan and Chase. He then joined the
commercial group of the Western Electric
Engineering Department as a storekeeper.
Early in 1918 he left for military service,
serving overseas with the 82nd Division.

After the war Mr. McEvoy |
returned to his former work ©
and a few years later was ©
placed in charge of general ©
storage at 463 West Street ©
and in outside warehouses. ~
At the close of the war there —
was a large quantity of ap- ©
paratus and equipment that
had been made for govern- —
ment uses. This was stored ©
in a warehouse on 36th Street. |
Mr. McEvoy had charge of
this and handled all details
of its final disposition. In
1928 he was made a super-
visor in charge of stores,
storage, models, samples, pat-
terns and plant stock.

ALBERT SCHREIBER of the Switching
Apparatus Development Department, with
over twenty-seven years of service in the
Bell System, died on November 14. Mr.
Schreiber joined the Engineering Depart-
ment of the Western Electric Company in
1913 and for the next four years, in the
Machine Switching Apparatus Department,
was concerned with the design and develop-
ment of various types of machine switching
mechanisms and also intimately associated
with the development of the panel apparatus
installed in the semi-mechanical offices in
Newark. From June, 1917, to May, Ig919, he
served with the 11th U. S. Engineers, most
of his time being spent in France.

Upon Mr. Schreiber’s return he continued
his machine switching development work,
but a year later transferred to the Dial
Apparatus Laboratory as a test engineer.
Previous to his death he had been responsi-
ble for setting up and maintaining all test
equipment that is employed in this labora-
tory, including the design of special testing
apparatus.

F. J. Repmonp visited the Hyattsville
office of The Chesapeake and Potomac Tele-
phone Company to inspect crossbar system
installations.

C. H. WHEELER and R. B. Bauer were in
the Hartford and Glastonbury, Connecticut,
offices of The Southern New England Tele-
phone Company to examine line and cut-off
relays that are in use in these cities.

V. B. Pike visited The Ohio Bell Tele-
phone Company, Cleveland, and the Illinois
Bell Telephone Company, Chicago, in con-
nection with demonstrations of new methods
for making temporary water-tight and gas-
tight closures for unsheathed portions of
lead-covered cables and for cable-end seals.

R. J. Nossaman, at Springfield and Bos-
ton on October 22 and 23, attended a con-
ference on drop wire and discussed other
outside plant matters with members of the
New England Company.

A. P. Jann, with members of the American
Society for Testing Materials, inspected the
hardware, sheet and wire samples exposed
at Brunot Island, Altoona, and State College,
Pennsylvania; Sandy Hook, New Jersey;
and Bridgeport, Connecticut.

C. S. Gorpon consulted with representa-
tives of the Navy Department at Washing-
ton on wire problems.

Mr. Gordon served as Chairman of one
of the Technical Sessions at the Annual Con-
vention of the Wire Association at Cleveland.
At this session, H. Blount and J. E. Wilt-
rakis of the Western Electric Company pre-
sented papers on high-speed wire drawing.

D. D. Haggerty discusses furniture for the new Bell Labora-
tories Club Lounge with officers of the Club. Left to right:
R. M. Burns, E. D.G. Paterson, Mr. Haggerty, R. 8. Alford

Would members of the Laboratories
be interested in seeing advance pro-
grams of “The Telephone Hour” in
the News Notes?

At THE BETHLEHEM office of The Bell
Telephone Company of Pennsylvania, T. C.
Campbell, L. N. Hampton, H. E. Marting
and P. W. Sheatsley, together with Haw-
thorne and Western Electric Installation
Department engineers, inspected the first
installation of Western Electric central-
office Jadders, ladder tracks and brakes.

D. E. Trucksgss visited Albany, Cincin-
nati, Detroit and Chicago to inspect regu-
lated-tube rectifier installations.

V. T. CALLAHAN was in Canton, Ohio, and
Lansing, Michigan, on reserve engine design.

At Lauretton, New York, H. E.
Marting, R. C. Johnson and J. W. Corwin
studied crossbar equipment problems.

A. E. Perris and F. T. Forster were in
Philadelphia to discuss storage battery prob-
lems. Mr. Forster was also in Washington
in connection with similar problems.

H. T. LancaBEeEr visited
Gaffney, South Carolina, and
Orlando, Florida, to inspect
repeater-station power plants
that have been rearranged for
automatic operation.

C. S. Know.ron was in
Philadelphia in connection
with the New York-Philadel-
phia coaxial installation.

W. A. MacMaster recently
spent a day at Wilmington,
Delaware City and Bayview
Beach, Delaware, inspecting
the coastal-harbor marine
radiotelephone facilities of The
Diamond State Telephone
Company.

R. E. Hersey and W. I.
McCu.tacu are at Newton,
Massachusetts, where they
will remain until after the cut-
over of the crossbar office now
being installed there.

G. A. Hurst and O. H. WILtirorp are
now in Detroit in connection with the intro-
duction of crossbar equipment in this area.
They will remain in Detroit until after
the cut-over.

E. W. Hancock was in Alameda, Cali-
fornia, in connection with the introduction
of crossbar equipment in this area.

H. N. Curistopuer and L. Y. Lacy have
been at Whippany testing wave-shape cor-
rective filters for rectifiers.

M. T. Dow, R. R. Houcu and H. W.
Nytunp of the Laboratories and L. G.
Adam of the Long Lines Department re-
turned from Texas where they had been
assisting in noise and crosstalk tests on the
Amarillo-Tucumcari cable project. R. P.
Booth, H. W. Evans, L. Hochgraf, W. E.
Reid, and M. A. Weaver were in Texas at
various times during October in connection
with this project.

P. W. Spence with J. O’R. Coleman of the
Edison Electric Institute attended the
annual meeting of the North Carolina sec-
tion of the American Water Works Associa-
tion at Raleigh on October 28 and 29. They
discussed the results of field investigations of
grounding made by the American Research
Committee on Grounding.

J. M. Dunuam accompanied by T. A.
Taylor of the A. T. & T. discussed with
engineers of The Bell Telephone Company of
Pennsylvania in Philadelphia inductive co-
ordination problems in connection with toll-
line dialing.

L. S. Insx1p, with T. J. Maitland of the
Long Lines Department, were in Eau Claire,
Wisconsin, in connection with lightning
protection on the Stevens Point-Minneapolis
cable. Mr. Inskip also discussed drainage
rectifier protection problems with engineers
of the Indiana Bell Telephone Company.

H. C. Franke, on a recent trip to Char-
lotte, studied the transmission stability of
type-K carrier circuits.

weeks in the vicinity of Chicago and Mil-
waukee in connection with tests on recently
installed type-K carrier systems between
these two cities. The tests included studies
of the possibilities of operating these sys-
tems with emergency arrangements which
would be required in case of severe damage
to a cable or a repeater station. Codperating

S. S. A. Watkins with false mustache and
mandolin contributed to the entertainment of
the farewell party at the Bell System Exhibit
of the New York World’s Fair. Mr. Watkins
had charge of the continuous training program
required for the Voder operators.

in the tests were G. J. Goetz, G. R. Smith,
M. W. Kyser and F. MacMillan of the Long
Lines Department in New York as well as
Long Lines plant people in the Western area.

Mr. Aikens also visited the transmis-
sion engineer’s office of the Wisconsin
Telephone Company to render assistance on
interference problems.

H. W. Ny unp visited Newark and Plain-
field to remove experimental installations
of 48-volt repeaters which have been on
trial at these points.

J. H. Incmanson and W. G. SrraitiFF
went to Point Breeze on matters pertaining
to rubber-covered wire.

E. D. Guernsey took part in an investi-
gation of noise induction in program circuits
of the New Jersey Bell Telephone Company
at Closter, New Jersey.

in the Sntployees’ Magazine Contest conducted by the Gmployees
Publication Section of the Sahery Council the Year

October 9 on the subject Variation of Cable
Loss With Temperature — Some Applied
Mathematics. He also talked on the same
subject to a group of upper classmen and
members of the mathematics and physics
departments at Miami University, Oxford,
Ohio, on October 14.

AT THE REQUEST of the National Broad-
casting Company, the New York Telephone
Company and the Laboratories have pro-
vided special television circuits from Madi-
son Square Garden to the NBC studios in
Radio City. The first use of these circuits
was during the recent presidential campaign
when both President Roosevelt’s and Wen-
dell L. Willkie’s appearances in the Garden
were televised. C. N. Nebel and D. S.
Barlow were responsible for circuit arrange-
ments during these speeches.

DurRING THE MONTH of October, F. E.
DeMotte, B. A. Fairweather, G. H. Huber
and V. M. Meserve worked on the Minne-
apolis-Stevens Point coaxial terminal in-
stallation.

J. F. Wentz was at the Point Breeze
Plant of the Western Electric Company for
two days in connection with their studies
of coaxial cable transmission characteristics.

At PuitapEtpuiA, C. N. Nebel, M. E.
Strieby, A. F. Mott and C. L. Weis made
experiments on an experimental circuit for
television transmission from Franklin Field

in Philadelphia and
discussed the prob-
lems involved with
representatives of The
Bell Telephone Com-
pany of Pennsylvania
and the Philco Radio
and Television Corp.

S. Dosa and L. W.
Morrison were in
Camden in connection
with some new meas-
uring equipment used
in television testing.

PROBLEMS IN CO-
AXIAL amplifier test-
ing were discussed with
Western Electric en-
gineers at Kearny by
M. E. Campbell, B. J.
Kinsburg and P. G.
Uppstrom.

THE COAXIAL REPEATER INSTALLATION on
the new cable from Stevens Point to Minne-
apolis is nearing completion and many trans-
mission tests are now under way. During
October, H. H. Benning, C. F. Boeck,
B. Dysart, M. M. Jones and B. H. Nord-
strom were engaged primarily in testing
the line-up and equalization of the Stevens
Point-Minneapolis coaxial system. K. E.
Gould, G. B. Engelhardt, and T. M.
Odarenko were engaged in making special im-
pedance measurements required in connec-
tion with television tests which will be
scheduled for next spring.

AT VARIOUS POINTS along the New York-
Philadelphia coaxial cable M. M. Bower,
J. J. Strodt and J. M. West investigated the
cause of certain intermittent troubles.

A DEMONSTRATION OF FREQUENCY-modu-
lated television signals was observed by
P. Mertz, W. T. Wintringham and N. F.
Schlaack on a recent visit to Camden.

Miss C. Marttice appeared before the
Board of Appeals at the Patent Office rela-
tive to an application for patent.

R. J. GUENTHER was at the Patent Office
during October to attend hearings before the
Board of Appeals and Primary Examiner in
interference proceedings.

L. E. Coon attended the 29th National
Safety Congress and Exposition held in
Chicago from October 7 to 11.

N THE larger cities, where there
are many central offices, ‘“‘informa-
tion” traffic is handled at one or
more centralized information bureaus,
where a group of “information”
operators serve subscribers of a large
number of offices. Some years ago the
No. 3 information desk* was designed
for this sort of service, and has come
into fairly wide use. Since it was in-
tended primarily for very large cen-
ters, such as New York and Chicago, it
was designed to accommodate at each
position four large local record binders
open on reading shelves before the
operators as well as a number of
smaller toll and auxiliary record
*Recorp, March, 1930, p. 328.

binders in directory racks. Although
modified arrangements for two infor-
mation binders were later made avail-
able, they did not permit as great a
reduction in the space requirements as
desired because of the basic section
design of the information desk.
There are, however, many multi-
office cities with centralized informa-
tion service that require only one, or
at most two, local record binders open
before the operators, and such bu-
reaus also require fewer toll and
auxiliary binders. They have rela-
tively small desks that do not contain
many of the desirable features of the
No. 3 desk. It is in these smaller
centers that floor space requirements

are more frequently a controlling
factor, and even the modified No. 3
desk might be larger than could
be conveniently accommodated. It
seemed desirable, therefore, to design
a new information desk framework to
secure the floor space economies that
the smaller number of records permits,
and still retain the advantages of the
circuits of the No. 3 desk. Such a
desk could then be used to replace
existing ones as occasion demanded.
As a result the No. 6 type information
desk has been developed. It uses the
same key equipment and circuits as
the No. 3, but provides a simpler and
smaller desk framework, and permits
easier installation procedures.

The new desk is designed on the
basis of using one or two large local
information binders per position. In
the one-book form it is known as the
6A desk, and in the two-book form as
the 6B, the latter requiring more floor
space than the 6A but less than the
two-book No. 3 desk. An installation
of the 6A desk in Dallas, Texas, is

Fig. 1\—The 6B information desk provides for two large local
information binders by a sloping rack between the cabinets

shown in the photograph at the head
of this article. Key and lamp equip-
ment is mounted in the two opposite
faces of a rectangular turret at one
side of the position. This arrangement
provides a double-sided desk with
two operators. A sloping shelf on each
side provides for the single informa-
tion binder, and the level space be-
tween the key equipments may be
used for a toll directory rack when
required. In place of the wooden up-
right partitions formerly used be-
tween operators, a new transparent
material is employed that has certain
minor advantages over the wood.

The 6B section, shown in Figure 1,
is like the 6A except that an addi-
tional sloping shelf is provided for
each operator in the space between
the key equipments, and it is for this
reason that the 6B is somewhat larger
than the 6A. Where toll and auxiliary
records are required, they will be
placed in a toll directory rack mounted
on top of this added sloping section.
When this is done, the lamps used to
call the supervisor,
shown on top of the
key cabinets in the
photograph at the head
of this article, will be
extended above the
toll directory racks on
pipe standards. The
additional upper slop-
ing shelf of the 6B desk
provides room for a
second local informa-
tion binder.

The supporting
structure for both of
these desks is the
framework and legs of
a commercial flat-
topped table. In a new
installation, these
lower units are all set

in place first, and a metal cable rack
is carried along them just below the
top. The upper units are then put in
place beginning at the end of a desk
line-up farthest from where the cables
enter. As each upper unit is put in
place, the cables attached to the key
panel are laid along the rack, as indi-
cated in Figure 2. This simplifies the
installation, since there is a minimum

These new desks require less space
than the corresponding No. 3 desks,
and this fact, together with the sim-
pler installation, reduced cost and
the desirable operating and service
features of the circuits of the No. 3
desk, makes them attractive for all
but the largest multi-office cities.

Fig. 2—In installing, the bases are all put in place first, and then the tops put on
successively beginning at the end farthest from the cable entrance

HE J2 carrier system provides
| twelve voice channels in each
direction in the frequency range
between 36 and 143 kc. As with all
the broad-band systems, twelve voice
channels are modulated with twelve
carriers at the transmitting terminal
so as to lie between 60 and 108 kc,
and then by two group modulations
the 12-channel band is translated to
the frequency position it will occupy
on the line. To help in reducing cross-
talk, four frequency allocations are
provided so that when several systems
are transmitted over the same pole
line, the channels of various systems
will be different from each other. The
carrier supply system must provide
not only the twelve carriers required
for the basic channel modulations, but
also those needed for the group modu-
lations for each of the four line allo-
cations. In addition each system em-
ploys two pilots to control the net
transmission loss, and the

and the modulating carriers required
are graphically shown in Figure 1.
Corresponding demodulations take
place at the receiving terminal. All
allocations use the same frequency,
340 kc, for the first stage of group
modulation. For the second modula-
tion, two carriers are required for the
w-E allocations, and four for the
east-west allocation. These are 364
and 484 kc for the west-east allocation
and 306, 308, 541 and 543 kc for the
east-west. Seven carriers are thus re-
quired for the group modulations in
addition to the twelve required for the
channel modulations. The positions
of the sidebands with respect to the
channel carriers are indicated in the
conventional manner. In the basic
group they are lower sidebands, and
the first group modulation retains
them in this position. The second
group modulations employing carrier
frequencies above 448 kc, however, in-

ke
NA, NB, SA, and ss. For the *
west-east direction, the NA a7th
and wnB_ allocations are 85th
alike, as are the sa and sB; gist
but for the east-west di- I2Ist
rection, all four are differ- 67th X2
ent. The frequency posi- 137th

vert the position of the sidebands
West west With respect to those employing car-
riers below 400 ke.

As with the type-K and other
broad-band carrier systems,* most of
the carriers are supplied by a 4-kc
oscillator and a harmonic producer.
From this source, filters pick out
twelve frequencies at 4-ke intervals
from 64 to 108 kc inclusive, and these
are used to modulate twelve voice
channels to form the basic group.
This derivation of all the carriers
from a single source is very advan-
tageous because regardless of slight
variations in the frequency of the
basic source, all the channels retain
the same harmonic relationship. Also,
any variation in frequency can be cor-
rected by an adjustment of one oscil-
lator, while if a separate oscillator
were used for each carrier frequency—
a total of nineteen is required for the
J2 system—each oscillator would
have to be adjusted separately. The
advantage of the harmonic generation
of carriers from a single source is of
particular importance in such a sys-
tem as the J2, where the modulating
frequencies are high with respect to
the line frequencies. Under these con-
ditions, and using independent oscil- J
lators for each carrier, the variations
of all the oscillators may add up and
thus give a net variation at the line
frequency that is much larger than
the variation of any one oscillator.
With carriers all derived harmonically
from a single source, however, the
variation in the final line frequency,
SA expressed in per cent, is always the
EAST-WEST same as that of the oscillator from
which the carriers were derived.

The 308, 340, 364, and 484-kce car-
= gr riers are all odd harmonics of 4 ke,
inthe Jasysiem and are selected by filters and suit-

other equipment for two carriers are
mounted on a single panel as shown
in Figure 2. The three other frequen-
cies, 306, 541, and 543 kc, however,
are not harmonics of 4 kc, and to
secure them, a §-kc oscillator is pro-
vided and used to modulate a har-
monic of 4 kc. By modulating 548 kc,
the 137th harmonic of 4 kc, with 5 kc,
the difference frequency of 543 kc
is readily obtained. For the §41-ke
carrier, 268 kc—the 67th harmonic of
4 kc—is modulated with 5 kc. The
products of any such modulation in-
clude, besides the sum and difference
frequencies, the sums and differences
between the multiples of 268 ke and
the odd multiples of 5 kc. Twice 268
plus 5 gives the required 541 kc. To
secure the 306-kc carrier, the connec-
tions of the 5 ke and of the 4-kc
harmonic to the modulator are inter-
changed, so that an even harmonic of
5 ke will be available. The 79th
harmonic of 4 kc—316 kc—minus
twice 5 kc yields the desired 306 kc.
The derivation of these various car-
riers is indicated in Table I.

A single-tube, fork-controlled oscil-
lator is used to supply the 5 kc. This
is quite similar to the 4-kc supply.
The circuit arrangement is shown in
Figure 3. A steel fork, operating in a
vacuum in a sealed container, has an

electromagnetic coil near each prong.
One is connected to the plate and the
other to the grid of the vacuum tube.
The coils are shunted by condensers to
tune their inductance, and the con-
denser shunting the grid coil is made
adjustable to give control of fre-
quency over a small range but it is
not expected that adjustment will be
needed except at long intervals. A
varistor is connected across the plate
coil to limit the voltage. The complete
oscillator unit is mounted on a small
panel, the front of which is shown in
Figure 4; the fork unit and a few other
elements are on the rear of the panel.

The modulating circuit with which
this oscillator is used is shown in
Figure 5. A copper-oxide varistor type

Fig. 3—Schematic of 5-kc oscillator used to
modulate odd harmonics of 4 kc to obtain
some of the group carriers

modulator is employed. The circuit
connections are the same for both
541 and 543-kc carriers; only the
filters are different. For the 306 kc,
the arrangement is similar, but the
connections of the 5-kc oscillator and
the 4-kc harmonic are interchanged
for reasons already stated. In all
cases amplifiers follow the filters.
Besides these seven carriers re-
quired for the first and second group
modulations, six other frequencies are

VARISTOR
541-KC
TO 5-KC OR
543-KC
OSCILLATOR
FILTER |
| 268-KC 000
To an RETARD
CARRIER |548-KC
GENERATOR | BAND
FILTER
VARISTOR
To 316-KC 306 KC
CARRIER | BAND , BAND
GENERATOR | FILTER FILTER
TO5 KC
OSCILLATOR 7

Fig. s—Block schematics of the two modu-
lating circuits used to obtain carriers of
306, 541, and 543 kc

needed to serve as pilots. For the
west-east transmission, the pilots are
at 40 and 80 kc on the line for all allo-
cations, and for east-west transmis-
sion they are 92 and 143 kc for all allo-
cations. For all west-east allocations,
40 and 80 ke are the positions that
would be occupied by the channel
carriers of 64 and 104 kc if they were
transmitted. All carriers are sup-
pressed in the channel modulating cir-
cuit, however, and these two fre-
quencies are resupplied as pilots.
Although the carriers are sup-
pressed in the channel modulator,
there is always a small amount of
carrier leak. The effect of this leak on
the level of the pilot could readily be
allowed for, but if the frequency of
pilot and carrier should differ some-
what, beat frequencies would result,
and would be objectionable. Such
beating is avoided by using the same
4 ke as source for both carrier and
pilot. It is necessary, however, that
the level of the pilot be accurately
constant, while slight variations in the
level of the carrier are unobjection-
able. This constant level of the pilot
is secured by using a second oscillator
whose frequency is locked by the 4-ke
harmonic and whose output is stabi-
lized by a lamp-resistance bridge in

the feedback path. The circuit in
simplified form is shown in Figure 6.
As the output increases, the lamps
heat up, and the bridge approaches
the balanced condition, decreasing
the positive feedback. Equilibrium is
reached when the loss in the lamp-
resistance bridge equals the gain in
the amplifier. In the vicinity of the
balanced condition, the circuit is very
sensitive and maintains a constant
output with considerable accuracy.
Variation in the level of the locking
frequency or in the gain of the ampli-
fier produces very little change in the
output since a small change in the re-
sistance of the lamps in the nearly
balanced bridge produces a relatively
large change in the loss. A 5-db
change in the input or in the gain of
the amplifier, for example, results in
less than a o.1-db change in output.

One locked oscillator is used for the
64-ke and one for the 104-kce pilot, and
their outputs are connected to a single
bus that supplies the two west-east
pilots for as many as ten systems.

It is desirable to have the pilots for
one direction of transmission all at
the same frequency on the line so that
the same pilot filters used with the
regulators can be employed for all
frequency allocations. This is easily
accomplished for west-east trans-
mission by selecting two of the carrier
positions for the pilots because these
remain carrier positions for all four
allocations. With east-west  trans-
mission, however, the carrier positions
for the different allocations are stag-
gered, so that if the same pilot
frequencies are to be used for all
allocations, they must fall outside the
transmitted band.

58 OR 60 KC
64 KC
TO TO
SYSTEM | SYSTEM !0
64 KC ONLY
TO ALARM
CIRCUITS
| DISTRIB-
UTING
MANN RESIS-
CHANNEL RESIS-
DISTRIBUTING —L. TANCE
SYSTEMS
TO ALARM
| CIRCUITS
104 KC ONLY
a |
104 KC Fig. 6—Supply circuit
ds for the production of
pilot frequencies
109 OR KC
128 December 1940

By selecting pilot frequencies, on
the line, of 92 and 143 kc, only two
pairs of pilot frequencies before mod-
ulation are required. These are 58
and 109, and 60 and 111 kc. Since
these frequencies are not normally
furnished by the carrier supply, sepa-
rate oscillators are used. The 58 and
10g are used for the nB and sB allo-
cations and the 60 and 111 for the
na and sa allocations. The oscillators
for these pilots are identical to those
of Figure 5 except that there is no
locking circuit, and instead, a crystal
is placed in the feedback circuit to
control the frequency, as indicated on
the diagram. One such pair of oscil-
lators supply the na and sa alloca-
tions, and one the nB and sB alloca-
tions. All these pilots are generated at
frequencies suitable for supply to the
circuit before the group modulations,
being at 58, 60, 64, 104, 109, and 111
ke. The effect of the two group modu-
lations in bringing them to their line
positions is shown in Figure 7.

The carrier supply equipment is
provided in duplicate, and a transfer
circuit is arranged to change to the
second supply if the voltage on the
first drops below a safe value. Trans-
fer requires only a few milliseconds.
An alarm is given whenever a transfer
is made so that the cause of the trans-
fer may be investigated, and a dif-
ferent alarm is given in the event of
total failure of supply. The pilot
supply is not provided in duplicate,
but alarms are given whenever the
level changes by as much as % db.

The arrangement of the carrier
supply circuit is in general the same
as that used for the type-K system.*
Two bays are required for mounting
the carrier supply equipment and
these supply terminals for ten com-
plete systems, or 120 talking channels.

brought very close to-
gether, even under rela-
tively low voltages, particles are torn
from the electrodes and may establish
a conducting bridge between them.
These conducting filaments form at
voltages less than the sparking po-
tential and are produced by the large
electrical forces which result from the
very small separation of the electrodes.
In experiments by G. L. Pearson,
bridges were formed between gold,
steel and carbon electrodes when
separated from 2 to 70x 1o%cm. The
voltage gradients were about ten
million volts per centimeter. To deter-
‘ mine the point of zero displacement,
electrical contact was made between
the electrodes. They were then sepa-
rated a known distance and the volt-
age between them slowly raised until
the bridges formed. This occurred at
voltages between 15 and 350 volts
depending on the separation. The
resistance dropped permanently to a
low value at the same time.

Measurements of the temperature
coefficient of resistance of the bridges
identified them as consisting of the
material of the electrodes and changes
of their resistance when the electrodes
were separated or brought together
slightly showed that they can be
pulled out and crushed. The separa-
tion of the electrodes was controlled
very delicately by attaching one of ~
them to a cantilever bar and adjusting
it with a micrometer screw. The other
electrode of the apparatus was
mounted on a fixed support. To in-
sure rigidity, the whole apparatus
was cut from a solid block of steel.

Conducting bridges form between electrons
when brought very close together even under
relatively low voltages

gatherers are alert to get
the information to the newspaper
offices as soon as possible. Since pic-
tures are often a very important part
of this information every effort is
made by the reporter to obtain suit-
able ones and to send them in without
delay. The promptness with which
pictures can be supplied from distant
points has been greatly increased in
recent years by the development of
satisfactory telephotograph equip-
ment, and the provision of per-
manent transmission networks with
fixed transmitting points in the more
important cities of the country.

For transmitting pictures from
other points, provision is made for the
connection of telephotograph equip-
ment to leased lines for semi-perma-
nent installations or to regular toll
lines for short intervals. In either case,
it is necessary to have an arrangement
for the connection between the tele-
photograph equipment and the tele-
phone line which will permit the send-
ing of satisfactory pictures, protect
the telephone line from high voltages
that may be present in the picture-
sending apparatus, and prevent the
sending of high signal levels which
might cause noise and interference on
neighboring telephone lines. Another
function required of a satisfactory

connection arrangement is a “‘holding-
coil action,” so that when the appa-
ratus is connected across the line, it
will draw sufficient current to “‘hold”’
the supervisory relay in the telephone
office, thus permitting the handset or
receiver to be replaced on the switch-
hook without releasing the line. This
is important because the telephone

Fig. 1—Schematic of the 105A coupling
unit for connecting telephotograph equip-
ment to working telephone lines. The 1044
differs from it only in the addition of a
switch and plug in place of the line terminals

transmitter, which might pick up
sufficient room noise to spoil the
picture being transmitted, is thereby
removed from the circuit.

To meet the demands presented by
the above requirements, two coupling
units—the 104A and t10osA—have
been developed. These units, shown
in the picture at the head of this
article, provide a simple means for
connecting telephotograph equipment
to working telephone lines, provide
the required holding coil action, and
at the same time protect the lines
from the possibility of
excessive voltages and

mission apparatus to the line, and a
third high-impedance winding con-
nected to a gas-filled tube.

The line winding has sufficiently
low resistance to take the required
supervisory relay current, and for the
protection of the line is insulated from
the other windings and from the case
sufficiently to withstand surges of
2000 volts.

The gas-filled tube connected to the
high-impedance winding is provided
to protect the line from excessive
signal levels. This tube has a nearly
infinite resistance at potentials below
about 75 volts. At approximately this
voltage, however, the gas in the tube
ionizes, and reduces the internal re-
sistance to a very low value. The
voltage ratio between the line and
tube windings of the transformer is
such that this ionizing potential corre-
sponds to a peak voltage on the line of
about 1.2 volts, which permits the
transmission of slightly over one
milliwatt of power into the line with-
out distortion. If, due to improper ad-
justment of the sending apparatus, ©
an input voltage corresponding to
higher power than this is applied to
the coupling unit, the voltage across
the tube exceeds the ionizing potential
and the tube, by virtue of the
impedance-transforming action of the
coil, imposes a low impedance shunt
across the line, thereby limiting the
voltage to approximately the critical

value. This character-
istic is illustrated in
Figure 2, which shows
the relationship be-
tween generator volt-
age and line voltage.
As may be seen, the
output voltage in-
creases linearly with
generator voltage up
to the point corre-
sponding to the ioniza-
tion of the tube. This
indicates no distortion
of the wave form. For
higher generator volt-
ages the output volt-
age increases only
slightly. In this range
the wave form be-
comes flat topped due to the peak-
limiting effect of the tube.

Although the action of the two
units is identical electrically, there
is considerable difference physically as
may be seen in the photograph. The
104A coupling unit is intended for
temporary installations, and is there-
fore provided with a handle for carry-
ing, a flexible cord terminated in a
plug, and a switch in the cord circuit.
The plug in conjunction with a jack
installed in the line by the telephone
company affords a ready means of
connection to the line. The 105A
coupling unit is intended for perma-
nent or semi-permanent installations,
and the line and apparatus windings
are brought out to screw-type termi-

Fig. 3—The 104A coupling unit with cover removed to show
the tube case at the left

To insure long life, the transformer
in both units is sealed to exclude
moisture. The tube is mounted inside
a small aluminum can which is, in
turn, assembled in the larger case with
the coil, and the connections between
the coil and tube are made by means
of the flexible leads with which this
tube is provided. The cover of the
104A unit is readily removable so that
if necessary the tube may be replaced.
This unit with the cover removed is
shown in Figure 3.

The development of these units has
been a factor in increasing the useful-
ness of one of the newer types of serv-
ice offered by the Bell System and
available for the use of the press.

assure quiet operation, and it is
required to develop an air stream of
such low velocity and low noise level
that a special set-up had to be made
in the Laboratories to measure it; also
a stringent vibration requirement
must be met.

In the tests a three-inch anemom-
eter is mounted in front of the fan and
twelve inches away from it. Measure-
ments are made opposite the center
of the fan and at one-inch intervals in
four directions along a vertical and
horizontal line which intersects the
fan’s axis. The anemometer is moved
outward until the air velocity be-
comes too small to measure accurately.

anemometer readings by dividing the
cross-section of the air stream into
rings one inch wide and concentric
with the axis of the fan. The area of
each ring multiplied by the average of
the four anemometer readings for that
ring gives the air flow through it and
the sum of these values the total air
flow. The rate of rotation of the fan is
measured with a stroboscope by de-
termining how many flashes per
minute make the blades of the fan
appear to stand still. Ordinarily, the
fans that are provided for telephone
booths circulate from 175 to 350 cubic
feet of air per minute.

To test for vibration fhe fan is
mounted on a platform on which rests
a vibrometer. By moving the vibrom-
eter about on the platform the vibra-
tion in different directions is found.

Les.ie R. Cox graduated from Purdue
University in 1922 with the degree of
B.S. in Electrical Engineering, and then
joined the Western Electric Company at
Hawthorne. After completing the stu-
dents course he was engaged in writing
installers’ specifications for panel machine-
switching exchanges. After a few years
outside of the Bell System, he joined the
toll development group of the Bell Tele-
phone Laboratories in 1929. Since then
he has been engaged in the development
of carrier terminals for broad-band sys-
tems. His principal interest has been
modulators and their carrier supply.

C. D. Owens received the degree of
A.B. in Physics from Indiana University
in June, 1928, and immediately joined the
Technical Staff of of the Bell Telephone
Laboratories. As-a’miember-of the Trans-
mission Apparatus Department he -has-
heen engaged in the development of con-
densers, loading coils, retardation coils,
and compressed magnetic powder cores.
During this period, he took part-time
graduate work at Columbia University
and received an M.A. degree in Physics
from this university in 1936. ,

D. W. Grant received the degree of
B.S. in electrical engineering from Kansas
State College in 1928. Coming at once to
these Laboratories, he joined the trans-
former group in the Apparatus Develop-
ment Department, where he has been
engaged in the development of audio-
frequency transformers for use in the tele-
phone plant and in specialty products
apparatus.

K. G. Van Wynen came to the De-
velopment and Research Department of
the A. T. & T. Company after receiving
the E.E. degree from Cornell University
in 1925. Until 1927 he was associated
with a group working on program trans-
mission problems. From 1927 to 1929
his work was on inductive interference in
connection with railway electrification.
Since 1929 he has been concerned with
the rating of transmission performance.
During this interval he has been princi-
pally interested in the design and con-
struction of circuit arrangements used in
field and laboratory tests. Mr. Van
Wynen also attended the Brooklyn
Polytechnic Institute where he received
the M.E.E. degree in 1933.

A. C. Gitmore joined the Laboratories
in 1916 and became associated with the
Materials Inspection group. Shortly after,
however, he transferred to the Systems
Department and for a number of years
was engaged in equipment drafting. In
1923 he joined the Equipment Develop-
ment group where he was first concerned
with the analyzation of Hawthorne orders
and later with trial installations. At the
present time he is engaged in the develop-
ment of equipment for central offices such
as that he describes in this issue.

devices some five years ago. Entering our
Physical Research organization in 1929,
he had behind him undergraduate work at
Willamette (A.B. 1926) and graduate
study at Stanford (M.A. 1929). His initial
assignment was to study thermal noise in
conductors, shot noise in vacuum tubes
and carbon noise in microphones. One of
these studies has been accepted by
Columbia University as a thesis for the
doctorate of philosophy. A collateral in-
vestigation of thermo-sensitive materials
grew eventually into a project under Mr.
Pearson’s direction, from which have
come a number of present and prospective
uses for thermistors in the Bell System.

Bell Laboratories Record  1940-12: Vol 19 Iss 4