The plug holes marked with Roman numbers (at the right on the receiver)
are connected to taps on the aerial or primary coil. The wave range of this.
coil is approximately as follows, with a proper aerial :
Condenser switch at
The turns on the detector or loose coupling coil are variable by means of the
switch located on its top, the wave range for each tap being marked.
Either of the two detectors can be used by means of the switch located be-
For receiving a signal of a known wave length the following procedure can be
1. Use tight coupling.
2. I?lug in on the aerial coil.
3. Set the switch on the detector coil at about " X=500/1000."
4. Turn the condenser very slowly over the entire scale.
5. Change the plug on aerial coil and repeat No. 4. When signals are finally
heard, the coupling and the position of the switch on the detector coil are
varied until the best results are obtained.
NOTE. In some cases two combinations of the aerial plug and condenser give
almost equally good results. The best one is that in which the larger part of the
condenser is used with condenser switch at " short waves " and vice versa, with
the condenser switch at " long waves." The aerial used with this set should
have a capacity of 0.0011 mf and a natural period of 450 meters.
The following detailed notes on the circuits and operation of the
set have been found useful as a result of actual work in the field :
Referring to connection diagram 75, it is seen that D. C. leads
marked 3 and 4 go to both receiving switches in series. It is therefore
necessary to have the main switches of both receiving sets in the same
position that is, cut off when sending, even though one receiving
set may have no aerial wire connected to it. A flash due to the break-
ing of this D. C. circuit will be seen at the rotary switch if the receiv-
ing set is cut in before the engine is stopped. The large double-pole
switch at the top of the receiver when closed so as to connect the
receiver to the aerial and counterpoise automatically disconnects the
sending side from the aerial and counterpoise. This feature is not
indicated in the diagram of connections where the receiving set when
cut in is apparently shunted by the sending set.
TRANSFORMER PRIMARY CIRCUIT.
From A. C. lead No. 1 to the primary inductance, to the snap
switch, to the ammeter, to the primary of the transformer, to the key,
and via A. C. lead No. 2 back to the generator. The voltmeter is
across the A. C. leads as shown. If the voltmeter shows voltage, but
upon closing the key no spark takes place at the spark gap, the snap
switch in the primary circuit is probably open.
The voltage, as indicated by the voltmeter, must never be more than
S5. If it is desired to change the generator frequency (and the pitch
of the note emitted), in order to secure greater selectivity for the set
when working in the presence of other sets having about the same
generator frequency, the engine may be slowed down or speeded up.
but the drop or rise in voltage incident thereto must be compensated
for by a change in the generator rheostat, so that the voltage will be
Connections for Sending
kept constant at 85 when using all the gaps of the spark gap. Any
violation of this rule will cause a breakdown in the transformer.
HIGH-FREQUENCY CIRCUITS TRANSMITTER.
Closed oscillating circuit. This consists of the condenser, vari-
ometer, and spark gap. It is to be noted that the variometer is com-
mon to both closed and open oscillatory circuits, and, therefore, that
66536 17 7
changing the variometer (which is the one at the left-hand side of the
chest and has scale divisions in wave lengths marked upon it) not
only changes the period to which the closed oscillatory circuit is
tuned, but also slightly changes the tuning of the open oscillatory cir-
cuit. A word of caution should be given concerning the switch marked
" Little " and " Great " which throws the coils of this variometer
from a parallel to a series connection or vice versa. This switch can
only be moved to the right or left to " Little " or to '* Great " when
the index is directly opposite the dividing line between the red and
the white divisions. Any attempt to throw this switch when the vari-
ometer coils are in any other position will only result in damage to the
OPEN OSCILLATORY CIRCUIT.
This consists of the aerial, aerial or loading coils, plug for cutting
in proper coil, the aerial variometer (marked from zero to 180), the
variometer common to both closed and open oscillatory circuits, the
hot-wire ammeter, and the counterpoise or ground.
The antenna supplied by the Signal Corps for this set has a natural
wave length of 450 meters and a capacity of about 0.0011 mf.
It is found by experiment that the set using the Signal Corps 80-
foot mast and rubber-covered counterpoise works best at about 1,000
meters, where the antenna hot-wire ammeter reads about 7J amperes.
CODING OF WAVE LENGTHS.
The great advantage of this set lies in the fact that any desired
wave length from 675 to 2,220 meters can be sent out at will and if
the wave length is changed after every word of a message, according
to a prearranged code of wave lengths for example, the first word
sent with 700 meters, the next with 2,100, the next with 1,400, etc. it
will be difficult for any eavesdropping operator who has not the wave-
length code to follow the changes of wave length with any success.
Hence, messages may sometimes be kept confidential even when sent in
plain English. This will take considerable drill on the part of two
men, the operator and an assistant, who will rapidly make the neces-
sary changes in the loading coils and variometers at a signal from
The first step will be to make experimental determination of the
combinations of loading coils and variometers necessary to produce
the best radiation for every wave length within the range of the set
and to set them down in the form of a table. Thus, starting with 700
meters, put the left-hand variometer at 700, put the plug in the hole
marked 675-1,080, and then slowly move the aerial variometer from
toward 180 until the hot-wire ammeter shows the best reading.
The various adjustments can then be noted in a table for future ref-
erence, thus: (The figures given are not the actual figures. These
must be determined for each set separately.)
-' mperes on
and so on, finding the best combination for every 50 meters increase
in wave length up to the limit of the set.
LIMITATIONS OF SYSTEM OF CODING WAVE LENGTHS.
It will be noted that there is one best wave for the set, namely,
about 1,000 meters. From some experiments made recently at Fort
Leavenworth it is concluded that it is safe to state that, up to about
75 miles over average land, the falling off of energy due to the use of
the longest wave lengths will not be so great as to prevent the use of
any wave length within the limits of the set (675-2,220 meters), but
that beyond that distance, up to the extreme daylight distance of the
set (about 185 miles), it would be safer not to work with any wave
length greater than 1,800 meters.
Only further experiments in the field, between two similar sets
working at gradually increasing long ranges, will determine the
greatest distance at which the whole scale of sending wave lengths
may be used.
From the table plotted as above, different codes of Wave lengths,
differing by many meters from each other, may be agreed upon, to
be changed daily in actual work, and confided to all operators con-
Connections for Receiving
Primary or aerial circuit. One lead from aerial comes through
combination switch to the primary of the transformer (shown on
the left of fig. 78), from there through plug contact to a point on
the little switch marked " Long waves "-" Short waves " ; and, if
the switch is thrown to the long-wave side, the circuit goes direct to
the ground; the variable condenser being then in parallel with the
primary of the transformer. If the switch is thrown to the short-
wave side, the variable condenser is in series with the aerial, the
primary of the receiving transformer, and the counterpoise or
The secondary or detector circuit consists of the secondary of the
transformer in series with the usual stopping condenser, connected
through the main switch to the detectors. The telephones are in
shunt to the stopping condenser.
The detector supplied is of the iron pyrites variety, which lacks
the sensitiveness of the Perikon. Any other detector may easily be
substituted for the detectors supplied with the set, the range of
which may be thereby easily increased.
With the switch thrown to "Long waves" the operator will get
the best results when using a small number of degrees of the variable
condenser and as large primary as possible, and, vice versa, with the
switch to " Short waves," which places the variable condenser in series
with the primary coils. The largest possible amount of capacity
of the variable condenser and the smallest amount of primary in-
ductance should be used for maximum strength of signals.
The combination switch which is used primarily to cut the receiv-
ing set onto the antenna and counterpoise simultaneously performs
several operations. Opening this switch disconnects the receiving
set from the antenna and counterpoise; automatically connects send-
ing set to the aerial and counterpoise; closes D. C. circuit of genera-
tor; disconnects detectors from secondary of receiving transformer,
thus opening that circuit and preventing detectors from being af-
fected by the spark when sending, and also opens the primary cir-
cuit of the receiving transformer. As the limits of the various coils
of the primary and secondary are marked, there should be no diffi-
culty about setting the receiving apparatus approximately for the
wave length of a station whose wave length is known. The operator
then varies his condenser, and also the coupling between the primary
and secondary of the receiving transformer, until he gets the best
adjustment. Changing the coupling (that is, pulling the secondary
away from or pushing it closer to the primary) changes the wave
length, though to not as great an extent as does varying the con-
denser. Some stations can not be heard at all well unless the secon-
dary coil is pulled some distance away from the primary. Practice
is the best guide to a working knowledge of the tuning of the receiv-
Figure 76 shows simplified schematic diagram of the transmitting
circuits. Figure 77 shows the generator circuits.
CALIBRATION IN WAVE LENGTHS.
The receiving set should be calibrated so as to locate the actual
combinations necessary for receiving the wave lengths sent out by a
similar sending set, either by actual tuning to another set sending
out successive wave lengths differing from each other by 50 meters,
as oiitli'ned above, 1 or by using the \vave meter provided with each
wagon set as a sending device, and with its coupling coil held near
the antenna lead, set up, consecutively, different wave lengths in
the antenna and make adjustments of receiving set necessary to tune
to the particular wave lengths sent out ; then compile a table showing
adjustments of condenser switch, primary, secondary, and variable
condenser necessary for each wave length in turn, so that the receiv-
ing operator can at once adjust his receiving apparatus to any desired
wave length, and, by quick changes, constantly follow, according to
prearranged code, the message sent out by the other station.
It is recommended that, in order to eliminate one adjustment of
the receiving set, the primary and secondary of the receiving trans-
former be kept in the same relative positions throughout; that is,
as close to each other as possible. This, while possibly sacrificing
efficiency, secures simplicity. The receiving operator's chart may be
arranged as follows:
Best receiving adjustments necessary to tune to wave lengths used
by similar wagon-set sending wave lengths shown in Table I.
NOTE. The condenser adjustments given above are not the actual ones necessary for wave lengths
And so forth for every 50 meters.
Constant drill in changing sending and receiving adjustments, car-
ried on between two or more similar sets, will result in remarkable
efficiency and rapidity, and the time necessary for transmission of
messages will be found to be but little increased over that required
w r hen sending on a single wave length.
RECEIVING BY CODING OF AVAVE LENGTHS.
Two complete receiving sets are provided with each wagon set,
though ordinarily only one is used. Two messages from different
stations may be copied from the same antenna without either operator
hearing the message copied by the other. To do this it is, of course,
necessary to have a lead from the aerial running to each of the receiv-
ing sets. A change in the tuning of one receiving set will call for a
slight readjustment of the other receiving set, however, in order that
the latter set may stay in tune with the given wave length.
RADIOTELEGRAPH Y. 103
The use of two receiving sets in parallel makes it comparatively
simple to folloAv a message sent according to a prearranged code of
wave lengths, for it is perfectly practicable to so arrange the wave-
length code that the waves of any length within certain limits will
fall within the limits of the condenser of either one set or the other,
and either one operator or the other, without making any change of
adjustment other than a mere movement of the condenser handle,
will have his apparatus constantly in resonance with the incoming
Thus, let us say that in the code agreed upon, which includes all
wave lengths between 900 and 2,150 meters, the first word will be
sent with a 900-meter wave, the next with 2,100, followed by 1,500,
1,850, 1,050, 2,000, etc.
The two sets are cut in at the receiving station and are each manned
by an operator. Operator No. 1, at the left, puts the plug in the hole
of the primary of his receiving set marked " 900-1410," couples his
primary and secondary as closely as possible, throws his receiving
switch to " Long waves," and puts the switch of the detector coil on
whatever coil will give him the strongest signals. He can then, by
merely moving his condenser from toward 180, tune his set to
any desired wave between 900 and 1,410 meters, and it will be his
duty to copy all words of the message which may fall within those
Operator No. 2, on the right, similarly throws his switch to " Long
waves " and plugs in primary coil marked " 1270-2150," and makes
the other adjustments as given for No. 1. He is then ready to receive
any wave between 1,270 and 2,150 meters by merely setting the
pointer of his condenser at the proper number of degrees on the
From Table II, prepared as before described, either operator can
set his condenser accurately and instantly to the proper reading for
any desired wave length within limits; hence when the message
is to be received the first word sent as per schedule at 900 meters
is copied by No. 1 operator, who has his pointer at the proper place
on the condenser scale; the second word at 2,100 meters by No. 2,
who has already set his pointer at the proper place. As the third
word is sent at 1,500 meters, No. 2 readjusts his condenser for the
next word, and later turns the pointer to the proper place for the
next word at 1,850; then No. 1 comes in on his set and copies the
next word at 1,050 meters, No. 2 the next at 2,000, and so forth, the
words being placed together in accordance with the order of their
receipt so as to make a complete message.
This method of using two operators saves time by dispensing with
a number of switch and plug changes, which a single operator would
have to make in using only one receiving set.
The method of using two receiving sets tuned as above could easily
be worked by one operator who could wear the single head receiver
of one set on one ear and that of the other on his other ear.
All these methods should be practiced continually to improve the
skill of the operators.
Care must be taken to close or open both main switches of the
receiving set at the same time when working both receiving sets
in order to prevent sending into one of the receiving sets and
burning it out.
FIELD RADIO PACK SETS.
The smaller size of portable sets, known as a field radio pack set,
has been made in several models designated by the number of the
year in which they were made. Owing to the rapid improvement in
design and construction, the 1912 model has become practically
Radio pack set, model 1913, 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.
1 receiving set.
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 crystal's.
1 canvas case for receiver.
1 connector, 4- wire (lower half), generator.
2 connectors, 2-wire (lower half), antenna and counterpoise.
1 copy " Radiotelegraphy."
RADIOTELEGRAPH Y. 105
1 speedometer (carried in operating chest).
1 cap for speedometer opening.
1 canvas hood.
Mast, type F. (Type D mast has 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 that 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 new type F sectional mast with short sections is superseding
the type D with long sections as the stock of the latter becomes ex-
hausted, as it has been found by experience that a mast with short
sections can be raised more easily from the ground than one with
long sections. The type F mast equipment consists of 14 sections,
each 4 feet 2 inches long or 5 feet 2 inches over all, including the
106 RADIOTELEGRAPH Y.
coupling tube. The 10 sections are used for the mast itself, 3 sec-
tions for the shelter tent when erected, and 1 extra section for use in
case one of the others becomes unserviceable.
When starting to erect the mast, the four antenna wires and guys
should be laid out on the ground at right angles to each other and
the umbrella insulator put on the upper end of the section that is not
provided with a coupling tube. This section should then be raised
and eight more sections with coupling tubes added, section by section,
the tenth and last section being the one provided with the insulator
fixed at the bottom end. During the erection the mast should be
kept as nearly vertical as possible by the men holding the distant
ends of the antenna guy ropes. Owing to the liability of the mast to
buckle, no attempt should be made to erect the entire mast at one
time ; that is, by coupling all sections together and raising by means
of the guys.
ANTENNA AND COUNTERPOISE.
The standard antenna is of the umbrella type with four radiating
wires, each 85 feet long, suitably insulated at the open ends and held
as nearly horizontal as possible by guy rope extensions, each 85 feet
long, the outer ends of which are made fast to ground pins. The
standard counterpoise has four radiating insulated wires, each 100
feet long, laid out on the ground under the antenna wires. Both
antenna and counterpoise wires are carried on hand reels for conven-
ience in packing and quick reeling and unreeling in setting up and
taking down the mast.
The generator is a hand-driven, 18-pole, alternating-current ma-
chine having an intermittent output of 250 watts at 110 volts and
500 cycles at a speed of 3333 R. P. M. It is self -excited, the exciting
current for the fields being generated by a small shunt- w T ound direct-
current machine, the armature of which is mounted on the same shaft
as the alternator armature. The exciter has two poles and delivers
the direct current at about 110 to 150 volts. The whole machine is
driven by two handles, which should be turned at the rate of 33
R. P. M. to give the necessary armature speed of 3333 R. P. M., the
combination gear having a ratio of about 100 to 1. The direction
of rotation of the handles must be as shown by the arrow on the top
of the gear case, as otherwise the machine will not deliver any cur-
rent. The w r hole is inclosed in a dust-proof aluminum case. To
obtain access to the commutator, remove the flywheel, taking care
not to lose the key on the flywheel shaft; then remove the large
brass nut and the aluminum disk held in place by the latter, after
RADIOTELEGRAPH Y. 107
which it will be found that the commutator is readily accessible,-
To remove the armature from the machine, proceed as above; then
take off the casing covering the spur gears at the opposite end of
the shaft, and the gears themselves; before removing the armature
take the brushes out of the holders to avoid injuring or breaking
The tension on both sets of the generator brushes should be kept
as light as possible consistent with good commutation. A small in-
crease in the friction of these brushes will require considerable ad-
ditional power to drive the machine. Both sets of brushes can be
removed when necessary through openings in the lower part of the
case, the D. C. exciter brushes being at the flywheel end and the
A. C. brushes at the opposite end.
A canvas cover is provided for the generator, which should be
kept on at all times when the generator is not in use.
A speed indicator is mounted on the upper part of the gear case
in sight of the men driving the machine so as to show if it is being
driven at the proper speed, at which time the red line on the moving
vane coincides with the black index or arrow at the window. The
vane is divided diagonally into black and white parts, the white
showing if the speed is too low and the black if too high.