Atlanta tri-weekly journal. [volume] (Atlanta, Ga.) 1920-19??, 1922-06-10

whose SUES, OuISluS Ol LLldL SSCIlOll
given over to the insulating panels,
are inclosed by expanded metal
guards which serve both to protect
the apparatus from injury and ia
prevent accidental contact with
those parts subject to high poten-
tial.
Four 250-watt vacuum tubes and
one 50-watt tube will be used for
transmitting. These tubes, which
have an Divide coated filament that
insures maximum electron omission
with minimum expenditure of fila
ment circuit power, are mounted in
the upper part of the framework Of
the transmitter. This location pro-
vides adequate ventilation.
Each of the vacuum tubes requires
a filament current of 6.25 amperes.
The current for heating the fila
ments is supplied from a constant
potential generator. The filament
current is adjusted and held con-
slant by means of the generator field
rheostat. The tubes are rated in
accordance with their filament re-
sistance, each tube being marked
with a designating letter A, B, G, D
or E. A separate adjustable resist
ance with stages correspondence
marked is placed in circuit with the
filament of each tube.
The radio transmitter is essential
ly a generator of radio frequency
energy IAN oscillation generator),
with means for modulating this
energy in accordance with current
variations produced by a microphone
operating in conjunction with an am
plifier and certain other auxiliary
equipment. The oscillator comprises
a tuned circuit which includes the
antenna system. This tuned circuit
determines the frequency and wave
length of the radiated energy.
Description of Equipment
The modulating system provides
means whereby the alternating cur
rents corresponding to speech or
| music are supplied in amplified form
| direct to the oscillator circuit. Oper-
alton of this system may be under
stood by considering that the plate
circuit of the oscillator is supplied
with. speech currents directly from
! the incubator. The combined cir
cults provide a sort of mixing cham
| Der in which the speech currents
are combined with the steady carrier
wave supplied by the oscillator to
produce the modulated wave re-
quired. The system of meditation
used in our equipments, in connec-
ton with Western Electric vacuum
tubes, insures the highest efficiency
in clearly reproducing speech and
music; in other words, complete and
| perfect meditation.
The frequency of the transmitted
energy (wave lengthy is controlled by
the value of the inductance in the
oscillatory circuit which includes the
antennae. This inductance is adj
i justed by means of a Veriometer.
| To provide this feature portion of
the oscillator coil included in the
antennae circuit is arranged to turn
on an axis at right angles to its nor
NAL axis so that the inductance of
the movable coil either aids or op.
poses the inductance of the re-
ma1nder of the coil. The movable
coil also serves to vary the coup.
ling between the antennae circuit
and that portion of the coil system
which is connected to the plates and
grids Of the oscillator tubes in a
| manner to insure satisfactory
operating conditions throughout the
frequency range for which the trans
mitter is designed.
A variable condenser connected
across the coil controls the plate cur
rent through the oscillator tubes,
and to- large extent the output Of
! these tubes. This condenser con-
sists of a variable unit in parallel
with two fixed units which may be
switched in or out of the circuit as
required. The variable unit is con-
trolled by knob on the front Of
| the set. Both the adjustable in
ductance and the adjustable con-
denser are provided with graduated
| dials so that after the transmitting
set has once been calibrated in con-
| nect1on with it's associated antennae,
wave length adjustments can be
| made without a wave meter.
The input equipment consists of
microphOnes, input amplifier, con-
troll apparatus, batteries and a loud
speaking receiver for monitoring
purposes, and may be operated by
talking close up or from a distance
of several feet. The microphone de-
sign is such as to insure faithful
reproduction Of every graduation of
tone of speech or music which is to
! be transmitted
Three Stage Amplifier
The microphone is mounted in a
casing which minimizes the effect of
mechanical vibration that might aft
feet the clarity of the reproduced
! sounds.
10 obtain the best results the mag
nitude of the feeble currents pro-
duced by the microphone must be
! increased many thousand times be-
fore they are impressed on the radio
transmitter. For this purpose an
input amplifier provides the neces-
sary amplification.
| This consists of a three-stage am
plifier mounted upon a black fin
ished angle iron framework so that
all items of the apparatus are &C.
cessible. The dimensions of the
framework are approximately five
feet high by two feet wide by ten
inches deep.
In addition. to the amplifier tubes,
| transformers, ETC., the input ampli-
f1er panel has mounted upon it con-
troll apparatus to regulate the am
plification.
Current to operate the microphone
is supplied by an 18volt storage bat
terry, and is regulated by rheostat'
on the input amplifier panel. Fila
ment current for the input amplifier
is obtained from the same 18-volt
storage battery that supplies the
current to the mfcrophone.
Suitable provision is made for
charging this battery, depending
upon whether the commercial cur
rent supply is alternating or direct.
Current for the plate circuit of
the amplifier should be at least 1870
volts. To enable the operator to
observe the loudness and quality of
| 1o1ivya,.ad fn q