The set is normally packed on three mules, but in emergency may
be packed on two. In normal packing the first mule carries the gen-
erator and six sections of the mast. The second mule carries the
operating chest, four sections of the mast, antenna, counterpoise,
accessories, bag, etc. The third mule carries the tent, with tent pins
and extension pieces folded inside, four sections of the mast, flag kit.
lanterns, etc. In emergency packing with two mules, the first mule
carries the generator and 10 sections of the mast, and the second the
operating chest, four sections of the mast, antenna, counterpoise, and
tent. Figures 81 and 82 show the present methods of packing.
1915 RADIO PACK SET.
The 1915 set is similar to the 1913 type and in general the same
instructions, etc., apply to it. It consists of the following units:
1 operating chest.
1 hand generator.
1 pack frames, set (3 frames).
Each unit contains component parts as follows :
Operating chest :
1 resonance transformer.
1 oscillation transformer.
1 sending key.
1 spark gap.
1 hot-wire ammeter.
Operating chest Continued.
1 receiving sol.
1 connecting cord for generator ( 4-conductor, with plugs),
1 connecting cord, with plug, for antenna.
1 double-head receiver.
1 test buzzer.
1 tool kit.
1 extra section for transformer secondary.
1 extra set crystals.
1 canvas case for receiver.
1 connector, 4-wire (lower half), generator.
RADIOTELEGRAPH Y. 121
Operating chest Continued.
'2 connectors, 2-wire (lower half), antenna and counterpoise.
1 flexible connector for antenna inductance.
1 connector, 2-wire, small, for receiving set.
2 spring hooks.
4 legs for chest.
1 copy " Radiotelegraphy."
Hand generator :
1 speedometer (carried in operating chest).
1 cap for speedometer opening.
1 canvas hood.
Mast, type F. (Type D mast h:is 1 top, 1 bottom, 5 intermediate and 3 extra
1 top section.
1 bottom section.
8 intermediate sections:
4 intermediate sections, extra (3 for tent).
9 carriers, wire.
4 pins, antenna.
1 set adapters for tent (4 pieces).
1 bag, antenna and counterpoise.
1 bag accessories.
Pack frames, set:
3 frames (1 set). Each frame is complete with cincha, 2 cincha straps
with rings and snap hooks, and 2 straps with snap hooks at each end.
2 guy ropes.
1 insulating device.
Complete sets should be designated as " radio pack sets, com-
plete" giving year and serial number, and should be so carried on
property returns, invoices, and shipping manifests.
Incomplete sets should not be so designated, but units in them
which are complete should be designated as under the unit heading
above and units tl\at are not complete should be designated as under
the component part heading. When units or component parts are
used to complete sets they should be expended.
Operating chests and hand generators should always be desig-
nated by the year and serial number, and masts by the type letters.
The essential differences in the two models are in the hand genera-
tor, the transmitting oscillation transformer, and the receiving set,
a brief description of which will be given.
The 1915 generator is a 24-pole machine, with a speed of 5,000
R P. M. The ratio of the gearing is 100 to 1, as in the 1913 ma-
chine, so that the speed of the handles must be 50 R. P. M. At this
higher speed less pull is required on the handles and the tiring effect
on the men is less than at 33 R. P. M. of the other machine.
On account of the higher speed, great care must be taken to keep
the D. C. commutator clean and the brushes properly fitted to it.
Failure of a machine to generate current is almost always due to a
Only a nonfluid oil should be used for lubrication of the gears and
ball bearings, and in the same quantity as in the 1913 machine.
The oscillation transformer consists of two open spirals inductively
coupled and a third spiral which is to be used as an antenna induc-
tance for obtaining longer wave lengths. This inductance is inserted
between the oscillation transformer and the antenna by transferring
the long flexible lead from the open circuit spiral to the inductance
which is in turn connected to the oscillation transformer by a short
flexible connection. Care must be taken to see that these added turns
do not oppose the turns of the oscillation transformer; that is, the
inside turns of one should be connected to the inside turns of the other.
Ordinarily the antenna inductance will not be in the circuit except
a few inches from the lid of the chest.
The wiring diagram is shown in figure 83, in which the heavy
wave lengths, and the dotted lines from it to the antenna inductance
and antenna are for the longer waves.
The open and closed circuits of the oscillation transformer are
electrically joined together at their base, to which the counterpoise
is connected through the control switch and ammeter. This method
of construction reduces the number of movable contacts from four
to two and also has the advantage that the outside metal rings may
be handled without danger of shock.
To put the set into operation : Connect the " Gen," " Fid," etc.,
plugs into the corresponding sockets ; connect the short flexible wire
from the rear binding post of the closed circuit condenser to the
small angle piece extending out at right angles from the base of the
oscillation transformer ; connect the long wire at the opposite end of
the condenser to the primary or closed circuit spiral, inserting the
number of turns corresponding to the desired wave length as given
on page 116, counting the turns from the outside turn inward; con-
nect the wire from the control switch to the open circuit spiral, the
exact number of turns to be found later by trial. The other end of
the spiral is already connected to the counterpoise through the
In tuning the circuits the two spirals should be swung apart from
8 to 10 inches. After the two circuits have been brought into
resonance, as indicated by the greatest deflection of the hot wire
ammeter, the coupling of the two circuits should be increased or made
tighter by gradually swinging the spirals closer together until the
ammeter deflection just begins to decrease. If a wave meter is
available or a distant station assists in the test, a single wave length
or " hump " should be radiated and a Clear note obtained, the number
of gaps being adjusted if necessary as previously described. Care
should be taken not to have too close a coupling.
When the standard closed-circuit condenser and oscillation trans-
former are used the wave lengths are very approximately given in
the following table :
Ware IcHf/thx of jtriinunj or closed oxciU(i1'n\<i circuit.
Wsive length, in meters:
NOTE. Turns counted from the outside turn inward.
RECEIVING SET, TYPE C.
In the earlier sets, types A and B, the two circuits were magneti-
cally coupled, that is, the current in the primary (open or antenna)
circuit induced currents in the secondary (closed or detector) circuit
by means of magnetic lines which passed from the primary coil
through the turns of the secondary coil. In the present set the two
circuits are statically coupled; that is, the current in the primary
circuit induces current in the secondary circuit by means of static
lines in two coupling condensers connected in the leads between the
circuits. The transfer of the energy from the primary to the second-
ary circuit for the operation of the detector and telephones is as effi-
cient in this type of connection as in the other. By choice of suitable
values of the coupling condensers no movement of the coils or changes
in coupling is necessary for the reception of any wave lengths within
the range of the set, as is the case in the former sets. This reduces
/ SHORT WAVE LENGTHS
/Antenna 300 T0 ?00 METERS
m . -^
^8^ Detector r
j \ j j ^*\ j
/ LONG WAVE LENGTHS
/, 500 TO 2400 METERS
U, , , _
O | jfp^
coupling Detector^ ( ^
o condensers | Vo")^
< r fi ""
TYPE C RECEIVING SET
126 RADIOTELEGRAPH Y.
the number of adjustments for tuning from 4 to 3, and at the same
time the set is much more rugged, as there are no moving parts. The
values of the coupling condenser have also been so chosen as to make
the set much more selective than the others; that is, it can receive
signals from a station on one wave length and cut out signals from
another station on a different wave length more completely than be-
fore. In addition to the above advantages, the set as a whole has been
found to be more efficient than the previous types.
The type C receiving set consists of two statically coupled circuits,
high-resistance telephones, stopping condenser, fine wire-galena de-
tector, switch for short and long wave lengths, three dial switches for
tuning, etc. The circuits are shown diagrammatically in figure 84.
The primary circuit consists of: (1) The antenna, which when the
control switch in the cover of the chest is thrown to the " Receive "
position, is connected by a double plug with flexible wires to the bind-
ing post on the set marked "A"; (2) two primary coils in series, one
large and the other small, the number of turns in both of which is
variable by means of the two dial switches marked " Primary ". On
each coil there are contacts, to 24, for tuning to different wave
lengths, the dial nearest to the binding post "A" being connected to
the large primary for large changes in wave length and the other to
the small one for small changes and fine tuning; (3) counterpoise
which is connected to the binding post marked " C " through the
double plug and control switch. There is no series condenser in the
antenna circuit for the reception of wave lengths shorter than the
fundamental wave length of the antenna, as in types A and B, as it
has been found not to be generally useful.
When comparatively short wave lengths are to be received, as
from 300 to TOO meters, the double-pole double-throw switch on top
of the set should be thrown to the position marked " Short." This
makes no changes in the primary circuit, but connects into circuit
(1) the secondary coil with the dial switch marked " Secondary,"
with contacts to 24 for tuning to different wave lengths; (2)
detector and telephones.
Short wave signals should be picked up by adjustments of the
large primary and the secondary dials and fine adjustments made
later on the small primary dial.
When longer wave lengths are to be received, as from 500 to 2,400
meters, the D-P D-T switch should be thrown to the " Long " posi-
tion. This makes no changes in the primary circuit, but disconnects
the secondary coil, which in this set is most useful only at short
wave lengths, and connects the circuits as shown in the second print.
As the secondary coil is not in circuit, only the two primary dials are
effective in tuning.
RADIO-TELEGRAPHY. ' 127
Long wave signals should be picked up only by adjustment of the
large primary dial and fine adjustments made later only on the small
RECEIVING SET, TYPE D.
This set is practically the duplicate of the type C, except that the
number of studs in the three dials has been increased so as to give
The Signal Corps has designed and built two sizes of automobile
radio sets, or tractor sets, as they are called (a) a "divisional"
tractor of 1 k. w. size; (ft) an "Army" tractor of 2 k. w. size.
The 1 k. w. set, complete with supplies and detachment of seven
men, weighs about 6,700 pounds, and on an average road is capable
of making a speed of from 20 to 25 miles per hour. It carries a
60-foot sectional mast, which can be raised in a few minutes by means
of guides on the roof of the tractor. The antenna is of the umbrella
type, with 16 radiating wires each 75 feet long. The counterpoise is
likewise of the umbrella type, laid on the ground with 8 w T ires, each
75 feet long. The transmitting set is of the quenched-spark type,
with inductively coupled circuits adjusted to radiate waves of 600,
800, 1,000, and 1,200 meters. The receiving set is of the statically
coupled type similar to that in use in the 1915 radio pack sets, but
of larger size and capable of reception of much longer wave lengths.
The 2 k. w. set, complete with supplies and detachment of eight
men, weighs about 9,000 pounds, and on an average road is capable of
making a speed of at least 15 miles per hour. It carries an 80- foot
sectional mast, which is raised in a manner similar to that in the 1
k. w. set. The transmitting and receiving sets are likewise similar to
those in the previous set, but capable of using much longer wave
DAMPING LOGARITHMIC DECREMENT.
The oscillations in a wave train in a single circuit of coil and con-
denser die down to zero, as shown in figure 13. Other things being
equal, the higher the resistance the more rapid is the decrease in
amplitude of each successive oscillation ; that is, the higher the damp-
ing; and, vice versa, the lower the resistance the less rapid is this
decrease and the smaller the damping. In every circuit in which the
resistance is constant any amplitude in the train is a constant frac-
tional part of the preceding amplitude.
It is possible to compare the relative amplitudes of the oscillations
in this way and thus to indicate the rate at which they decrease. For
purely theoretical reasons, however, the measure of the damping has
been taken as the natural logarithm, sometimes called naperian or
hyperbolic logarithm, of the ratio of two successive amplitudes in the
same direction. The symbol for this expression which is constant
for a wave train is generally written 5. Thus Iog e j 1 = 5, where Ij
is the amplitude of any oscillation as at B, in figure 13, I 2 the
amplitude of the next oscillation in the same direction as at F ; and 5
is the logarithmic decrement, or simply decrement, the significance
of which term will be given later. Although the amplitudes are both
positive, the same formula applies when both amplitudes are nega-
tive. In both cases the amplitudes are one complete oscillation apart
and hence the decrement when so measured is called the decrement
per complete oscillation. In a few cases the logarithm of the ratio
of two successive amplitudes in. opposite directions is used, in which
case the decrement is per half oscillation, and numerically it is one-
half the decrement per complete oscillation. The decrement per
complete oscillation is always used in practical work in this country.
Natural logarithms are indicated by writing the letter e as a sub-
script ; thus, log 2 where e is the base of the natural system of log-
arithms, s being the number 2.71828. (In some cases in books on
pure mathematics the subscript may be omitted.) No subscript is
used with the common or ordinary logarithms, the base of which
Tables of natural logarithms are sometimes used, although not
convenient for most computations. The natural logarithm can, how-
ever, be found by multiplying the common logarithms by 2.3026;
thus, log 3.000 = 0.4771, Iog e 3.000 = 0.4771 X 2.3026 = 1.099, as would
be found directly in a table of natural logarithms.
The expression 5 = log e =p can be written 5 = log I t log I 2 , the
logarithm of the fraction being the logarithm of the numerator minus
the logarithm of the denominator. The expression can also be
written log e I A d = log e I 2 , in which form it is seen that as d is con-
stant for any one wave train, the natural logarithm of the amplitude
of any oscillation can be obtained by subtracting the constant quan-
tity 5 from the natural logarithm of the next preceding amplitude
in the same direction. The term logarithmic decrement, or simply
decrement, as mentioned above, thus receives its name from the fact
that it is the constant quantity by which the logarithm of any ampli-
tude must be decreased so as to give the logarithm of the next ampli-
tude in the same direction.
A simple illustration of the decrement is given in the table below,
where in the first column are given the numerical values of the
successive amplitudes in a wave train, beginning for convenience
with a value of 10. Each amplitude is a constant fractional part,
0.818 approximately, of the preceding; in the second column is the
common logarithm of the amplitudes; in the third column the
natural logarithm; and in the fourth column the decrement
6=log e I 1 -ldg I 2 .
From this table it is seen that the decrement of this wave train
is 0.20, which is very closely represented in figure 14. Similarly in
figure 13 the decrement is 0.4 and in figure 15 in the case of un-
damped oscillations it is zero.
MEASUREMENT OF LOGARITHMIC DECREMENT.
The subject of damping and its measurement in terms of the
logarithmic decrement is one of the most technical parts of the
66536 17 9
subject of radiotelegraphy so that only a brief outline of the simplest
cases can be given here.
The logarithmic decrement can be measured either directly by a
decremeter which is a modified form of a wave meter or by a wave
meter if it is provided with a suitable means of indicating resonance.
When a wave meter is adjusted to resonance with a circuit in which
oscillations are taking place it will be found that the larger the
resistance in the circuit the broader will be the tuning in the wave
meter i. e., the greater will be the change that must be made in
the wave-meter condenser to make any decrease in the wave-meter
current from the value at resonance. Similarly the larger the resis-
tance in the wave-meter circuit the broader will be the tuning. On
the other hand the smaller the resistances in both the circuit and
the wave meter the sharper will be the tuning. As has been pre-
viously stated on page 128, the less the resistance in the circuit the
less will be the damping, and hence the smaller the logarithmic
decrement. Thus it is seen, in a general way, that there is a relation
between the shape and breadth of the resonance curve and the decre-
ment of the circuit under measurement.
It has been shown by theory that if the resonance curve is taken
by a wave meter under certain standard conditions, a simple formula
can be used to find the logarithmic decrement of a circuit. For this
purpose the wave meter should have a variable condenser witli a
suitable scale, graduated from to 180 or to 90 degrees, with
which there is furnished a calibration curve of the capacity of the
condenser, and the wave lengths indicated by the meter; and ti hot-
wire wattmeter with a suitable scale, connected as shown in figure 48.
The wattmeter indicates the value I 2 R in fractions of a watt, where
I 2 is the square of the current flowing in the wattmeter wire and
R is its high-frequency resistance. This wire is generally made of
a special alloy w T hich does not change its resistance appreciably
with heating and hence the product PR, that is, the watts on the
scale of the wattmeter, can be taken as relative values of I 2 , and of
the squares of the currents in the wave-meter circuit. Thus if for
two different currents the wattmeter scale deflections are 0.35X1/10
watt =0.035 watt and 0.0175 watt, the relative values of I 2 are 1
The logarithmic decrement of a circuit can be measured as follows :
Couple the wave meter loosely with the circuit and adjust the vari-
able condenser until resonance is obtained. Adjust the coupling
slightly until the wattmeter needle is on some convenient scale divi-
sion at or near full scale reading. Note this wattmeter reading. I R 2
and the condenser capacity, C R . Without changing the coupling ad-
just the variable condenser toward the zero end of its scale; that is,
for smaller values of capacity and for shorter wave lengths than at
KADIOTELEGRAPH Y. 131
resonance until the wattmeter reading is reduced to one-half of its
value at resonance. Note this reading, - = Ij 2 , and the condenser
capacity, C t . Similarly, without changing the coupling, adjust_the
variable condenser toward the 180 end of the scale, that is, for
larger values of capacity and for longer wave lengths than at reso-
nance until the wattmeter reading is again reduced to one-half its
value at resonance. Note this reading -|- = I 2 2 = I 1 2 and the con-
denser capacity C 2 . From the readings taken at resonance and on
both sides of resonance, the following formulas can be used to de-
termine the desired decrement, in which 5 t and 8 2 are, respectively,
the logarithmic decrements of the wave meter and the circuit under
measurement; x= 3.1416; C R is the capacity of the condenser in
microfarads or other convenient units, where resonance was ob-
tained, and G! is the capacity, where the wattmeter current was re-
duced to one-half its value at resonance on the short-wave length
side of resonance, and C 2 is the corresponding capacity on the long-
wave length side. The formula as usually written gives the sum
of the two decrements, from which the decrement of the wave meter,
which is given as a part of the calibration of the instrument, must
be subtracted to give the desired decrement. Two measures of the
decrement can be obtained from the above values; the first from
the readings at the resonance point and one side of the resonance
curve, and the second from the resonance point and the other side
of the curve.
For the capacity at resonance C R and that on the short-wave
(J _ (J
Similarly for the capacity at resonance C R and that on the long-wave
side C 2 :
P _p p _p
t> i p. ^ Jg >. V7 R c\ i i ^V. V/o
C 2 C 2
As the resonance curve is not always symmetrical it is best to take the
average of these two values for the average value of the sum of the
Instead of computing two values and taking the average, the fol-
lowing single formula, using the values on both sides of resonance,
gives approximately the same value for the sum of the decrements:
132 RADIOTELEGRAPH Y.
It will be noted that the values of I R 2 , I t 2 , and I 2 2 , do not appear in
the formulas but rather C R , C 1? and C 2 , which however depend on the
relative values of I R 2 , Ij 2 , and I 2 2 .
The following numerical example will show the use of the formulas,
the data being taken from the resonance curve of figure 85, where, as
described on page 62, a single turn of wire had been inserted in the
antenna of a quenched-spark set, the two circuits of which had been
carefully tuned to resonance as described on page 60.
Resonance _ . 001195
. 007 _______________________________________________ 0. 00115
From the plot of the curve in figure 85 it is seen that at resonance
I R 2 = 0.038 C R is 0.001195 mf.; and at Ii**-nf- C t is 0.001175 mf., and
at I 2 2 = -7r C 2 is 0.001225 mf.; hence
Average value, 8 1 -|-&o=0.065
Using the single formula
i 2 .
The value of 8 X being given with the wave meter as 0.016, it is seen
that 5 2 =0.066 ^=0.050 by both formulas, which is the logarithmic
decrement per complete oscillation of the antenna circuit.