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With control N on position 3, the radio transmitter
works into a series resonant circuit providing "current
feed" and inductive loading. The antenna circuit is
resonated by means of a continuously variable
rotating inductor, control M. This circuit is used for
operation below the fundamental frequency of the
antenna.
With control N on position 4, the antenna circuit
is identical with that obtained on position 3 except
that an additional tapped inductance, controlled by
ANT. IND. SWITCH, P, is added in series with the
rotating inductor. This circuit is used when the
operating frequency is relatively far below the funda-
mental frequency of the antenna.
It is recommended that the operator check the
possible resonance of coil, item 1170 of Fig. 1, at
operating frequencies above 4500 kilocycles. Although
this coil is not connected in the antenna circuit, the
inherent capacity coupling may cause absorption of
useful radio-frequency power. Absorption may be
easily determined by placing control switch P at sev-
eral points while watching the antenna current. Con-
trol P must not be allowed to remain at a point which
indicates a decrease in antenna current. In general,
it will be found that no difficulty will occur if the
following points are used.
Transmitting Tuning Unit
P Switch Position
TU-7-B
2
TU-8-B
5
TU-9-B
5
TU-10-B
5
The antenna resonance is then made in the usual
manner using controls M, N, and possibly 0.
For operation in the frequency range of 150 to 800
kilocycles, the externally connected Antenna Tuning
Unit BC-306-A is used. This unit contains the neces-
sary inductive reactance to resonate specified antennas
at frequencies well below their fundamental. The
variation in inductive reactance is provided by the
ANTENNA VARIOMETER SWITCH, control E,
and the ANTENNA VARIOMETER, control F.
The proper connections are described in SECTION II,
INSTALLATION. In general, it will be necessary
to use Antenna Tuning Unit BC-306-A with Trans-
mitter Tuning Unit TU-26-B. The antenna loading
equipment contained in the radio transmitter will
resonate a 400 micromicrofarad antenna to approx-
imately 650 kilocycles. Therefore when the minimum
inductance is reached on the Antenna Tuning Unit
BC-306-A (E = 2, F = 0), place control E in position 1
which disconnects this unit. Proceed to resonate the
antenna circuit with control N on 4. Control M is
the continuously variable inductance between induc-
tance steps on control P.
Under some conditions it may be found that one
coupling tap will not give sufficient loading while
the next higher tap will give overloading of the trans-
mitter. In this case use the higher coupling tap by
slightly detuning the antenna circuit and keeping
the p-a dial C tuned to a minimum plate current
until the normal transmitter loading of 210 to 220
milliamperes total plate current is obtained.
• 16. DYNAMOTOR UNIT PE-73-C
Starting and stopping of the dynamotor unit is
controlled remotely by the OFF-ON switch at the
Radio Transmitter BC-375-E. No adjustments are
required or provided on the dynamotor unit.
When operated at full-rated load continuously for
M hour the temperature rise of the dynamotor will not
exceed 55 degrees Centigrade. However, if the dyna-
motor is operated for a greater length of time, even at
lighter loads, without being allowed to cool off, its
temperature will continue to increase and will ulti-
mately reach values which are injurious to the
insulation and may even burn out the windings.
This also applies to the starting relay. If it is desired
to operate the dynamotor unit continuously at full
load for a period greater than IA hour (such as for
testing purposes in the laboratory), the end bells of
the dynamotor and the cover of the relay-fuse box
should first be removed. The dynamotor unit can then
be operated at rated load continuously for any period
of time without injurious heating. Care should be
exercised to place guards around the dynamotor unit
when operated in this manner so that the operators
cannot come in contact with exposed high voltages.
When operated in conjunction with the transmitter,
the dynamotor operates at practically zero load unless
the key or microphone switch is closed. Continuous
operation under this condition will not result in
overheating although the transmitter should be turned
off whenever possible between the periods of trans-
mission.
17. REEL RL-30-B
Braking, locking and winding operations are
controlled from the crank on the reel. Normally the
reel is in the locked position such that the wire will not
unwind from the spool. Reeling-in is accomplished by
rotating the crank in a clockwise direction, as indi-
cated by the direction arrow Wind on the nameplate
at the center of the reel spool. A ratchet mechanism
on the spool prevents the wire from unreeling when
the crank is released. By rotating the crank in a
counterclockwise direction the braking mechanism
is released, thereby permitting the wire to be reeled
out. Braking force decreases gradually as the handle
is rotated through approximately the first 40 degrees
of its motion. Beyond this point, and up to the
extreme limit of its motion the brake is completely
8
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