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Section II
Paragraph
2
AN 08-40SCR274-2
When Antenna Relay Unit BC-442-AM is furnished the
capacitor can be added if necessary by the use of the
HKit tor conversion of Antenna Relay Unit BC-442-AM
to Antenna Relay Unit BC-442-A".
(3) MODULATOR UNIT.-Locate the modulator
unit near the 24-28 volt d-c supply and the radio equip
ment. Use a minimum of connecting cable.
(4) RADIO CONTROL BOXES.
( a)
Install the radio control boxes so that they
are accessible to the pilot and co-pilot.
1. Locate the receiver radio control box so that
the dial can be easily read day or night. Use Radio Con
trol Box BC-473-A or BC-473-B for one receiver, Radio
Control Box BC-496-A for two receivers, or Radio Con
trol Box BC-450-A for three receivers.
2. Locate the transmitter radio control box so
that the three switches and built-in key can be easily
operated.
(b)
Allow clearance below the boxes for inser
tion of plugs.
(5) TUNING SHAFTS, CONNECTORS, ETC.
(See figure
5-8.)
( a)
Keep the flexible tuning shafts short, as
straight as possible, and avoid all sharp bends. Be sure
that the receiver radio control box dial corresponds with
the dial of the receiver to which it is connected.
(b)
Coupling MC-211-A (right angle) may be
used as a link between Tuning Shaft MC-2I5 and a
receiver if necessary. This coupling can be used within
certain limits at the control box end of the tuning shaft
but it should be omitted altogether if a satisfactory in
stallation can be made without it.
(c)
Plug PL-15I-A may be plugged into either
one of the side receptacles on the receiver racks.
(d)
Make ground leads as short as possible. Con
nect a short flexible lead from the airplane frame. to one
of the uG" binding posts on each of the racks, in order
to secure a good ground connection to the receivers and
transmitters.
( e)
Provide bonding across at least two shock
mounts at each mounting.
(f)
Safety-wire the snap-slides which lock the
several units to their mountings.
(6) ANTENNA RELAY UNIT BC-442-A (or
BC-442-AM).-In general Antenna Relay Unit BC-
442-AM will be furnished and will provide satisfactory
operation for most antennas. If proper tuning of the
transmitter is not possible dlle to large antenna capaci
tance or inductance, series capacity may be added in
series with the antenna by the use of Antenna Relay
Unit BC-442-A or by the use of the
ffKit tor Conversion
of Antenna BC-442-AM to BC-442-A".
c.
CABLE CONNECTIONS.
(See fig.
5-9.)
( 1) Interconnection of the units can be accom
plished by any one of three methods of wiring:
( a)
By use of plugs and individual wires run in
both rigid and flexible conduit.
(b)
By use of plugs
I
and individual wires run in
flexible conduit only.
( c)
By use of plugs and individual wires with
out shielding.
(See fig.
5-10.)
(2) These methods should be accomplished
accordance with Air Corps Specifications 32300-A,
323I0-A and other Air Corps instructions, including
wiring diagrams which may be issued from time to time.
2. ADJUSTMENTS.
WARNING
Dynamotor DM-33-A, on the modulator unit
of this radio set, generates 600 volts direct
current, which is sufficient to �ause severe
shock, or even death. Make absolutely certain
that the dynamotor is not running before
making any adjustment whatever with the ex
ception of tuning up the transmitter.
a.
EQUIPMENT REQUIRED.-A small screw driver
or alignment tool is required.
b.
ANTENNA CIRCUIT ALIGNMENT OF THE
RECEIVERS.-AIt receivers must be connected to the
antennas or antennas with which they are to be used.
(1) Set the ttCW-OFF-MCW" switch on the con
trol box controlling the first receiver, to UCW" position.
(2) Set the UA TEL.-B TEL:' switch of the same
control box section to uA TEL." position.
(3) Connect Headset HS-33 and Adapter MC-
385-(
)
*
into any ttA TEL." jack or into a correspond
ing interphone jack box.
(4) Set ttINCREASE OUTPUT" knob for max
imum output.
(5) Rotate uTUNING" knob until the dial indi
cates the highest frequency. Do not attempt to rotate
the dial beyond the boundary calibration marks.
(6) Turn uALIGN INPUT" knob on the front of
the receiver for maximum background noise.
(7) Set uCW -OFF -MCW" switch to "OFF"
position.
(8) Perform a similar operation with each of the
other receivers in turn.
(9) Repeat the alignment operation on all receivers
for optimum results even though the improvement may
seem small.
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