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Section III
Paragraphs
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AN
08-40SCR274-2
SECTION III
OPERATION
WARNING
Dynamotor DM-33-A on the modulator unit
of this radio set generates 600 vol!s direct cur
rent. This is sufficient to cause severe shock
or even death. Make absOlutely certain that
the dynamotor is not running before making
any adjustment whatever with the exception
of tuning the transmitter. Do not remove the
transmitter tube covers while the set is 0per
ating as this exposes the high voltage. The
receiver and transmitters are calibrated di
rectly on the tuning dials. The operator should
be careful not to tune be�nd the normal end
frequency. End stops are� provided, but if an
unreasonable amount of force is supplied dam
age can be done to the equipment. Never leave
the airplane without setting the .. T R A N S.
POWER" and the "CW-OFF-MCW" switches
to their "OFF" position.
I.
STARTING AND STOPPING EQUIPMENT.
a.
TO START EQUIPMENT.
(1) To start the receiver equipment place the
"CW-OFF-MCW" switch on the receiver radio control
box to
"cw"
or "MCW."
AU
receivers may be oper
ated at once.
(2) To start the transmitter equipment place the
"TRANS. POWER" toggle switch on the transmitter
radio control box to "ON" position. Only
one
trans
mitter may be operated at a time.
b.
TO STOP EQUIPMENT.
(1) To stop the receiver equipment place the
"CW-OFF-MCW" switch on the control box to "OFF"
position.
(2) To stop the transmitter equipment place the
"TRANS. POWER" toggle switch to "OFF" position.
2.
OPERATION.
a.
RECEIVER OPERATION.-Operation of the re
ceivers of Radio Set SCR-274-N may be accomplished
by local and remote control or just by remote control,
by either one or two operators, and with any or all of
the four receivers. The type of installation determines
whether control is to be remote or local or both.
(1) REMOTE CONTROL.-Radio control boxes
are provided as part of this radio set for remote con
trol of the receivers. These radio control boxes providf
for control in one location of all the receivers, or for
control in one location of part of the receivers and in
another location of the remaining receivers. When re
mote control boxes are used, each receiver so controlled
must be equipped with an Adapter FT-230-A. For
remote control proceed as follows:
( a)
Set the "A-B" switches to "A" position.
(b)
Plug the headsets in the "A-TEL." head jack.
(
c
)
Set the "CW-OFF-MCW" switches to either
"CW" or "MCW".
(d)
Turn the "TUNING" controls to the desired
frequencies on each of the receivers.
( e)
Use the "INCREASE OUTPUT" controls to
adjust the volume. The gain controls of these receivers
may be used to amplify the signal from one receiver by
advancing the "INCREASE OUTPUT" knob of that re
ceiver, and feeding the signals from the others at the
same time so that only the one receiver signal is heard.
Note
For airways radio range signals keep the vol
ume to a minimum usable level by manipula
tion of the "INCREASE OUTPUT" control
on the receiver control box, to avoid incor
rect indications of the off course signals.
(f)
In case the radio control boxes are split
between two operators, both should follow the above
directions. In case the operator wishes to receive the
other operator's signal, he must turn his "A-B" switch
to the "B" position (presuming that the interphone
system is connected to the "B-TEL." jacks.)
(g)
Turn the "A-B" control to midposition to
cut off the signal.
(2) LOCAL OPERATION. - Adapter FT-260-A
and Control Unit MC-237-A are provided with this
radio set for local control of the receivers. The same
directions apply for local operation as for remote con
trols. The "A-B" switch for local operation is under
the front of each receiver, and, must be in the center
position when the receiver is remotely operated.
b.
TRANSMITTER OPERATION. - Transmission
may be accomplished by using any of the four trans
mitters of Radio Set SCR-274-N, however, only one
may transmit at a time. Radio Control Box BC-451-A
is provided for the selection and control of the trans
mitters.
CAUTION
Do not switch from one transmitter to another
while transmitting and
do not operate
Dyna
motor DM-33-A for extended periods of time
if the transmitter in use is not properly tuned
to the antenna.
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