B



c

tilt



FIG. 72.

to different spark frequencies or to group tuning, as it is sometimes
called. By the use of such a variable condenser and of a telephone
with adjustable pole pieces it is often possible to increase the loudness
of signals and the selectivity of the circuits without making changes
in the tuning.

In some types of circuits the fixed condenser serves another pur-
pose, as shown in figure 68, where it prevents the short circuiting of
the battery by the coil, in which case it is often called the stopping
or blocking condenser.

CALIBRATING WAVE LENGTHS OF RECEIVING CIRCUITS BY
MEANS OF THE WAVE METER.

In the previous illustrations of the wave meter it was used to
receive oscillations from a transmitter and to measure its wave
lengths. It may, however, be used to send out oscillations of known
wave lengths of comparatively feeble intensity like a miniature trans-
mitter. Several types of circuits may be used to excite the meter, as



RADIOTELEGRAPH Y. 85

a buzzer shown in figure 72, where A is a battery of not more than
two dry cells, B is the buzzer, and L C is the meter. This circuit is
sometimes known as the ~buzzer vwthod of excitation of the wave
meter which thereby becomes a source of slightly damped oscilla-
tions. The action of the buzzer circuit seems to be that at each spark
at the buzzer contacts, the meter condenser is charged and then dis-
charged through the inductance and thus sets up oscillations, inde-
pendently of the charging circuit in a manner similar to that of a
closed circuit as charged by the secondary of the A. C. transformer.
If a circuit is brought near the coil L and loosely coupled with it
the meter will induce in the circuit oscillations of the wave length
or frequency corresponding to the setting of the wave meter con-
denser. The circuits of a station receiver connected to the station
antenna may be calibrated by this method.

This circuit may be used in making many measurements and tests
in radio work, such as inductance, capacity, sensitiveness of tele-
phones, detector, etc.

RADIO APPARATUS IN USE IN THE SIGNAL CORPS.

The Signal Corps has installed 10 radio stations in Alaska, varying
in size from 1 kilowatt at Petersburg, Wrangell, and Kotlik to 8
and 10 kilowatts at Fort Gibbon, Fort Egbert, Nulato, and Nome.
Stations of from 3 to 5 kilowatts have been installed at St. Michael,
Circle, and Fairbanks.

In the Philippines stations have been installed at Manila, Fort
William Mcinley, and in the coast defenses of Manila, including a
set of 8 kilowatts at Corregidor.

In the United States 1 or 2 kilowatt sets have been installed in
several of the Coast Artillery districts ; 1-kilowatt set at Fort Wood ;
3-kilowatt set at Fort Riley ; an 8-kilowatt set at Fort Sam Houston ;
sets of from 1 to 5 kilowatts on 14 transports and cable ships; and
sets of from one-eighth to 2 kilowatts on the harbor boats assigned to
Coast Artillery districts that have a shore station.

All the Alaska and the Philippine stations except Corregidor have
their generators driven by gasoline engines. The generators in the
Artillery districts and on the harbor boats are nearly all driven by
motors from local electric power. The Fort Wood station may be
operated either from a gasoline engine or the local electric-light
plant. The Fort Riley and Fort Leavenworth sets are operated
directly from city power.

Two types of portable field sets have been issued by the Signal
Corps. The smaller size, known as a field radio pack set, is fur-
nished to the Organized Militia as well as to the field companies, and
is described on pages 104 to 127. The range of these sets under nor-



86 KADIOTELEGRAPHY.

mal conditions is about 25 miles over land, but much greater over
water. Thus one of the one-eighth kilowatt sets, with a 100-foot
mast, at Habana has worked with the naval station at Key West,
a distance of about 110 miles.

The larger size of field sets, known as a wagon set, is described
on pages 93 to 104. It is of 2-kilowatts output and is carried on a
two-chest pintle wagon, one chest with the engine and generator
and the other with the transmitting and the receiving apparatus.
The range of these sets varies from 75 to 800 miles, depending on
favorable weather conditions, time of day or night, character of
the land between the sets, etc.

FORT SAM HOUSTON STATION SET.

The following description of the Fort Sam Houston station is
given as an illustration of the type of .the 8 and 10 kilowatt sets in-
stalled by the Signal Corps in Alaska and in the United States.

Towers. These are of structural steel, about 200 feet high, 28 feet
square at base, and 4 feet square at top. The towers are supported
on concrete piers, each leg resting on a cribwork of timbers 12 inches
square, painted with insulating compound for preservation and in-
sulation. Timbers are bolted to the piers and to each other, the
bolts from the towers not extending down into the concrete. The
towers are about 300 feet apart.

Antenna. The antenna is of the T type, the flat top part of
which is composed of 7 wires, each 280 feet long and 4 feet apart.
Both ends of these wires are insulated with 18-inch electrose in-
sulators. The vertical w y ires, reaching from the center of the flat
top to the station, are each 180 feet long, separated 4 feet, and at
the bottom are joined together and carried as a single wire for
about 10 feet into the station through a porcelain wall insulator.

Counterpoise and ground. Connections are made to the water-
pipe system as a ground, but the most dependence is placed on a
counterpoise, described on page 56, which covers about half an acre
of land.

Poicer equipment. The alternator is belted to a single-phase, 60-
cycle, 20-horsepower induction motor driven by electric power fur-
nished from San Antonio. The motor can be automatically started
by closing a switch on the operator's table. In places where such
power is not available, as in Alaska, a Fairbanks & Morse 20-horse-
power gasoline engine is generally used. The motor speed is 1,750
R. P. M., the diameter of its driving pulley is 12 in., the diameter
of the driven pulley on the generator is 14| in., thus giving the
normal generator speed of 1,500 R. P. M. This machine is of the
inductor type, separately excited by a 1.5 kilowatt D. C. exciter on



KADIOTELEGRAPHY. 87

the same shaft as the A. C. armature, and delivers the power of 8
kilowatts, at a frequency of 500 cycles, 150 volts, 65 amperes, with a
power factor of about 82 per cent.

Switchboard. The switchboard is mounted close to the operating
table and contains the 500-cycle frequency meter, A. C. ammeter and
voltmeter, the exciter D. C. ammeter and voltmeter, and generator
field rheostat for the adjustment of the alternator voltage. The 500-
cycle wattmeter and the antenna hot-wire ammeter are mounted else-
where.

Transformer. The transformer in use is of the Closed magnetic
circuit type and oil immersed, as mentioned on page 23. The spare
transformer is of the open magnetic circuit type with dry insulation,
with a reactance in its primary circuit for the proper adjustment of
these circuits, as mentioned on page 25.

Key. The key is of the relay type, controlled by an ordinary
Morse key, which uses the direct current from the exciter to operate
the relay. The Morse-key contacts are shunted by a condenser to cut
down the sparking.

Condenser. The closed-circuit condenser consists of 26 Leyden
jars, covered with copper foil, each of a capacity of 0.002 mf. im-
mersed in oil to reduce the brush discharge, as mentioned on page 33.

Inductance. The closed-circuit inductance is in the form of a helix
wound with flat strip and adjustable only by steps for certain pre-
determined wave lengths, contact being made on the step correspond-
ing to the desired wave length and the secondary or open circuit
tuned to resonance with the closed circuit.

Spark gap. The gap is of the quenched type with plates of copper
but with a heavy plate of silver for the sparking surface, as men-
tioned on page 42. The separators are of mica. The gap is cooled by
a blower driven by an electric motor taking power from the direct-
current exciter.

Open or radiating circuit. As this set is of the directly connected
type, the closed-circuit inductance is included in the open circuit.
The coupling is made loose by the use of antenna loading inductance,
variable by steps for approximate resonance, and an antenna variom-
eter for fine adjustment between these steps, as described on page 35.

Receiving set. This is of a statically coupled type similar to that
in the field radio pack chest but of larger size for use with longer
wave lengths and provided with both tuned and untuned secondary
circuits. Both galena and audion detectors are used, the latter partic-
ularly for faint signals and distant stations.

COAST ARTILLERY STATION SET.

The following directions and instructions should be used in the
installation and operation of the 1-kilowatt Marconi 500-cycle sets
supplied by the Signal Corps for use in the Coast Artillery stations.



88



EADIOTELEGEAPHY.




RADIOTELEGRAPHY.



89



Installation. Install the motor-generator in a level position,
securely mounted on a solid foundation, preferably of concrete, Jill
the bearings with oil, and take care that the oil rings are working
properly. Connect the apparatus as shown in figures 73 and 74,
locating the quenched gap, oscillation transformer, antenna induc-
tance, and switchboard so as to be easily reached by the operator at




BACH V/EW

FIG. 74.



the key. Locate the antenna ammeter where it can be easily seen
from the operator's seat. Ground the middle points of the carbon-
rod protective devices on some ground other than the one used for
the antenna circuit. In the case of A. C. motor-driven sets, one-
half microfarad condensers should be used as protective devices in
addition to the carbon rods.



90 KADIOTELEGRAPHY.

Operation. The generator may be driven either by a D. C. or an
A. C. motor. In the case of the A. C. motor set, the machine starts
as a repulsion motor, with the armature short-circuited through car-
bon brushes on the commutator, and when nearly up to full speed
the brushes are automatically lifted from the commutator, which is
short-circuited at the same time. This change of connections con-
verts the motor into an induction motor. In motors of this small
size, start the machine by closing the main A. C. switch. No means
is provided for the regulation of speed. In the case of the D. C'.
motor set, start the machine by closing the switch of the automatic
starter and adjust the speed by means of the motor-field rheostat
until the frequency meter reads 500 cycles. Connect into circuit 8
gaps of the quenched gap. Close the switch to the generator Melds
and adjust the generator voltage by means of the generator field rheo-
stat until the A. C. voltmeter reads about *JOO volts. Make certain
that the spark-gap blower is running, which should have been started
when the generator field switch was closed. Set the switch of the
primary of the oscillation transformer on the desired wave length.
CAUTION: Never move the primary switch which controls the wave
length when the key is closed. Pull out the handle of the secondary
of the oscillation transformer 3 inches or more. Then close the gen-
erator armature switch and press the key. Rotate the handle of the
secondary of the oscillation transformer until the antenna ammeter
shows a maximum reading. NOTE: It is intended that the h<i>t<Uc*
of the oscillation transformer and antenna inductance can be turned
when the key is closed without danger of shock. If no maximum is
found and if the reading increases as the number of turns in the
secondary increases, connect in some of the turns in the antenna
loading coil. If no maximum is found and if the reading increases
as the number of turns in the secondary decreases, set the switch of
the primary of the oscillation transformer on a shorter wave length.
Rotate the handle of the antenna inductance until a maximum is
found. In some cases it is possible that a maximum can be found
without using the antenna inductance at all. Next adjust the cou-
pling by pushing the handle of the secondary in until the highest
possible reading of the antenna ammeter is obtained. It may be
necessary to make slight changes in the number of turns in the
secondary simultaneously with this adjustment, but the amount of
this change should be not more than one-eighth to one-fourth of
a turn. See that the frequency meter reads 500 cycles when the key
is closed and adjust the note of the transmitter until it is a clear
high whistle or note characteristic of this frequency. This note can
be heard in the telephones of the receiving set by leaving it connected
to the ground but disconnected from the antenna and adjusting the
detector until the note is heard. If the generator voltage is too low.



RADIOTELEGRAPH Y. 91

the note will be clear, but of low pitch ; if too high, the note will be
rough or hissing. If a clear note is not obtained by the adjustment
of the generator voltage, make slight changes in coupling and pos-
sibly in the number of turns in the primary and secondary of the
oscillation transformer until the desired purity of note is obtained,
but these changes should not appreciably reduce the antenna ammeter
reading. If after these adjustments have been made, the wattmeter
does not read the full 1 kilowatt, open the generator armature and
field switches to avoid the danger of a shock and connect in two or
three more gaps to give the necessary increase in power. Close both
switches and increase the generator voltage until the note is again
clear and of the proper pitch. CAUTION : Never touch any circuit
which may be alive without 'first opening the generator field or arma-
ture switches, preferably both; note that opening the key does not
render the high tension circuits safe to handle, because there is a
reactance coil shunted across the key which permits a sufficient flow
of current to render the high-frequency circuits dangerous.

It will be noted that the gap contains gaskets of two colors, gray
and red, which are of slightly different thicknesses, the gray being
thinner than the red. The two colors are to berinterchanged depend-
ing on whether or not full power is obtained when all the gaps are
used. If more than 1 kilowatt is obtained, substitute a gray gasket
for a red ; and, vice versa, if less than 1 kilowatt is obtained, substi-
tute a red gasket for a gray one. As delivered by the manufacturer
each gap is assembled with a proper number and kind of gasket and
a full set of spares is provided. The number of gaskets in place will
generally be correct, but, on account of small variations in spacing
which may take place when the gap is opened for cleaning, it may be
necessary to change gaskets from one color to the other.

The gap when received is in proper condition for working and
should not be opened until absolutely necessary. This necessity is
made evident either by the radiation falling below its usual value
when the circuits are properly adjusted or by inability to get a clear
note or a considerable reduction in the wattmeter reading when the
proper number of plates is connected up.

Under ordinary conditions it ought not to be necessary to open the
gap more than once in two or three weeks, and in case of any trouble
with the set all adjustments should be gone over carefully before
opening the gap. When it becomes necessary to do this, loosen the
set screw in the end of the gap and lift out the plates. It will prob-
ably be found that the gaskets and plates are stuck tightly together.
A wrench is provided for breaking the plates apart, and this wrench
is to go over the gasket, the wrench being given a slight twist until
the plates separate. Do not twist enough to damage the gasket.
Any irregularities found in the surface of the plates should be



92 EADIOTELEGRAPHY.

smoothed off with fine emery and the plates wiped perfectly clean
before inserting in the gap. The gaskets are expected to keep the
sparking space air-tight, and if such is the case the surfaces of the
plates will be found to have a bright granulated appearance. If,
however, the space has not been air-tight, the plates will show black
surfaces.

In case the gaskets stick so tightly that opening the gap tears the
surface off the gasket, the plates should be carefully cleaned and a
new gasket inserted. The tightening bolt of the gap should occasion-
ally be tried to see that it is perfectly tight, and if not should be
made so.

Owing to the slight compression of the gaskets which takes place
in time it will probably be found that this bolt can be turned from
one-eighth to one-half a turn. It will be found after the gap has
been in use for some time that one more plate will have to be con-
nected in for full power, and also that the gap improves somewhat
with use and that the radiation will be somewhat higher after it has
been in service for a short period.

If when the gap is opened a plate is found whose sparking surface
is partly black and partly bright, it is not an indication that the
gap is leaking air, but that this particular plate may not have been
in use long enough to consume the air between the plates when first
put together. Ordinarily this condition will be found only on the
plates which are not in use at all times, or if the gap is opened after
being in use only a short time.

After the plates have been put back in the gap the set screw at the
end should be tightened up again, and to secure air-tightness it should
be screwed with a great deal of pressure, about all that an average
man can exert with a 12-inch monkey wrench.

The base of the quenched gap should be connected to ground, a
screw in the base being provided for that purpose.

If at any time it becomes necessary to get at the contacts of the
oscillation transformer or aerial inductance, set the instrument on the
edge of a table with the slotted side of the base overhanging. Insert
a screw driver or other convenient tool in one of the holes of the
perforated cover and press down on it, when the cover will be found
to slide down through the slot, exposing completely the coils and con-
tacts. If at any time a contact appears to stick at the spiral con-
ductor, it can be lubricated with vaseline.

In case it is desired to work at wave lengths other than those
marked on the oscillation transformer, the movable coil of the oscil-
lation transformer may be used as a primary and the fixed coil as
secondary, in which case any wave length up to the limits of the
apparatus may be obtained. When using this arrangement the
switch should be set at the 1,200 meter mark for medium and long



RADIOTELEGRAPH Y. 93

wave lengths and at whichever of the other positions may be neces-
sary for the shorter wave lengths. The adjustment of the two xdr^.
cuits to resonance and to the proper coupling should be made as
previously described. If it is desired to work at less than 400 meters,
it will be of advantage to use two condenser jars instead of three
and to substitute red gaskets in the spark gap instead of gray ones to
obtain full power.

It is advisable to close the switch short-circuiting the ammeter
and open the voltmeter switch on the board after the set has been
tuned up, as it protects them from the jerk due to opening and
closing the key. Owing to the very large drop in voltage when the
key is closed the reading of the frequency meter may not be very
plain, and if such is the case the key may be opened and the first reed
which starts to vibrate after opening the key indicates the fre-
quency when the key is closed. Usually, however, the motion of the
reed is sufficient with the key closed except when working at reduced
power. It is possible to operate at any power between J and 1J
kilowatts by cutting in circuit the right number of plates and making
proper adjustment of the generator voltage.

When working at 1 kilowatt, with proper adjustment of all cir-
cuits, the A. C. ammeter will read between 10 and 11 amperes and
the A. C. voltage will vary between 125 and 150 volts with the key
closed. The power factor will vary between 80 and 85 per cent. All
of these readings will vary somewhat with the wave length used,
the constants of the particular aerial with which the set is used, and
the adjustments made, but will generally be within the limits men-
tioned.

FIELD WAGON SETS.

The following are the general instructions for the operation and
care of the Telefunken two- wagon 2-kilowatt set:

Engine. The engine supplied with this set is a water-cooled, single-cylinder
gasoline engine with a normal speed of 1,500 R. P. M., and the same general
directions as to care and operation which apply to water-cooled gasoline engines
in general apply in this case, and the principal points are briefly as follows :

Before starting make sure

1. That the water tank is full.

2. That all bearings have been oiled.

3. That the engine has sufficient lubricating oil by means of the stopcock on
under part of crank case. If it drips when opened, there is sufficient oil.

4. That there is sufficient gasoline in the tank as indicated by the gauge on
the front of the tank.

5. That the main switch of the generator is open.
To start

1. Open gasoline feed cock.

2. Prime carburetor by plunger on top.



94 RADIOTELEGRAPH Y.

3. Set the governor control handle (just above (lie mink) vertically, i. e.,
halfway across the scale.

4. Set the spark-control lever on the magneto on bottom notch.

5. Crank.
After starting

1. Make sure that the fan is running.

2. Close main switch.

Speed: The speed, as indicated by tin- tachometer on the engine, is controlled
by the position of the governor control handle (directly over the crank) and
by the position of the spark-control lever on the magneto (at the right), and
the best position of each for any particular speed i.^ best and easily determined
by experiment.

To shut clown temporarily

1. Open main switch of generator.

2. Press button on front of magneto until engine stops.
To shut down permanently

1. Same as above.

2. Ditto.

3. Turn off gasoline.

4. In cold weather empty all water out of every part of cooling system by
means of the cocks provided for that purpose.

Generator. The alternating-current generator supplied with this set is of tin-
inductor type with the field and armaimv winding stationary, and has there-
fore no brushes or sliding contacts of any kind. Its normal voltage is 85. The
exciter is an ordinary low-voltage direct-current machine. The voltage of the
alternating-current generator is varied by means of the rheostat in series with
its field. The rheostat is located in the lower left -hand coi'ner of the front
part of the instrument wagon. The connections between the power wagon
and the instrument wagon are made by means' of a flexible armored four-
conductor cable having the sockets so arranged that the terminals can be in-
serted only in the proper manner, the circuits of the alternator, exciter, etc.,
being shown in figure 77.

Transmitter and receiver. The connections of both are clearly shown in the
drawing and require no further description.

To adjust the transmitter for any wave length within the range of the set
proceed as follows, assuming that the desired wave length is l.ooo meters:

1. If it is intended to send at full power, adjust the voltage of the generator
by means of the slide rheostat (at the left) to about 85 volts.

2. If it is intended to send at less than full power, short-circuit one or more
of the gaps by means of the clips provided and at the same time reduce the
generator voltage about 10 per cent per gap short-circuited.

3. Set the primary variometer (at the left) at the wave length desired, viz,
1,000.

4. Put the aerial-coil plug (at the right) in hole No. 1, marked GSO/1050.
This adds sufficient inductance to the aerial to bring the final adjustment within
range of the aerial variometer.

5. Make the final adjustment with the aerial variometer (also on the right
and on one side of the aerial coils) by turning it slowly up from zero until the
ammeter in the aerial or ground circuit indicates a maximum.

6. The transmitter is now adjusted for the most efficient production and
radiation of the wave length selected when used with the aerial and count er-
poise supplied with the set.

Receiver. To receive, close the large double-pole switch at the top of the
receiver.