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5. CORDS
The cords to be used with the various radio sets
are listed in the parts lists for same. Schematic
diagram (Fig. 1) shows the necessary cording for the
Radio Transmitter BC-375-E. Plug PL-64 and Socket
SO-44 contain the necessary interconnections for the
radio receiver and transmitter control.
6. ANTENNAS
Because of the wide variety of antennas in the
radio sets of which Radio Transmitter BC-375-E is
a part, no specific details will be given for antenna
installations. However, the following general pre-
cautions should be observed:
1. The antenna and ground leads should be made
as short as possible, except where the length of lead-in
is definitely determined by the placement of radio
set and antenna.
2.
Antenna leads should be insulated to withstand
radio-frequency potentials as high as 5000 volts.
3. Antenna leads should be so placed that operat-
ing personnel will not come in contact with them
during normal operation of the equipment. Points
accessible to personnel should be covered with
Isolantite beads.
4.. Ground connections should have as low resist-
ance as possible. In aircraft installations the ground
path should be well bonded. The GND post should
always be connected to the ground system by a
short lead, allowing, of course, for flexure due to
vibration and shock. A link will be required between
posts LOAD A and LOAD B when Antenna Tuning
Unit BC-306-A is not used.
5. Antenna leads between the antenna and radio
transmitter and between the radio transmitter and
the radio receiver should be located as far as possible
from any primary wiring of the airplane. This applies
especially to the wiring to the dynamotor unit and is
necessary in order to decrease the pick-up of electrical
interference by the antenna circuit wiring.
7. ANTENNA TUNING UNIT BC-306-A
This tuning unit is provided with Mounting FT-142.
It should be mounted so that the tuning controls will
be accessible during operation. It is desirable that the
length of leads between the.radio transmitter and the
antenna tuning unit be kept to a minimum and that
the leads be well insulated.
' Terminals A-TRANS and B-ANT on the antenna
tuning unit are connected to LOADING TERMI-
NALS A and B respectively on the radio trans-
mitter when operation is with the low-frequency
transmitter tuning unit (Transmitter Tuning Unit
TU-26-B). However, at high altitudes (above 15,000
ft) and frequencies below approximately 400 kc,
better operation may be obtained by connecting
terminal A-TRANS on the antenna tuning unit to
the antenna post on the radio transmitter; placing a
jumper between LOADING TERMINALS A and B
on the radio transmitter; and connecting the antenna
to terminal B-ANT on the antenna tuning unit. This
alternate connection should be used only if it is
necessary to reduce the r-f voltages at the radio
transmitter because of high altitude flashovers. The
sensitivity of the radio receiver may be reduced
slightly. The post marked GND on the antenna
tuning unit should always be connected to the radio
transmitter ground.
8. REEL RL-30-B AND CONNECTOR
CLAMP MC-163
The reel should be mounted in such a position that
the crank is readily accessible and the counter is
visible. In order to prevent excessive "piling" when
the wire is being reeled in, the reel should be mounted
at least six inches above the fairlead and so placed
that the point at which the antenna wire leaves the
spool is in line with the axis of the fairlead; that is,
for best operation there should be no bends in the
antenna wire between the point where it leaves the
reel and the far end of the fairlead. The four mounting
bolts can be inserted in the reel base through the hole
provided in the web of the spool. Unless the mount-
ing screws themselves are grounded, a heavy ground-
ing wire or strap could be clamped under the nut of
one of the mounting screws for the purpose of thor-
oughly grounding all metal parts of the reel.
To fasten the antenna wire to the bottom of the
spool channel it is first necessary to remove the
spool cover by withdrawing it forward over the spool.
This can best be done by placing the fingers of both
hands on opposite sides of the cover and pressing
on the spool with the thumbs. The end of the wire
should be looped under the anchor pin in the spool hub
and then twisted around the wire proper a few times.
The twisted loop should then be placed in the groove
and all of the wire wound on the spool by turning the
crank in a clockwise direction. At this point the cover
should be replaced by passing the wire through the
slot opposite the wire opening and pushing the cover
over the spool until it rests against the flange on the
back plate. The cover should now be rotated so that
the wire from the fairlead to the spool will not rub the
edges of the wire opening in the cover either when
the spool is full or nearly empty. The counter should
now be set to zero. This should be done each time the
reel is used in order to reduce the error in the reading
caused by irregularities in winding.
Electrical connection to the radio transmitter is
made by means of Connector Clamp MC-163, the
installation of which is as follows :
a.
Remove the brass bushing from Connector
Clamp MC-163 by loosening screw in top of cover
2
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