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TM 11-5825-270-23
setting of R32 determines the delay (in seconds) after
(1) See that the power cord is connected to the
which an alarm condition will be indicated by the
receiver, and plugged into a grounded ac outlet.
receiver. Note the 0 (zero) setting of R32 represents the
(2) See that the antenna cable connector is
minimum delay, approximately 100 mSEC.  Typically,
properly mated with J1 (RF 1/P 50 ohm) at the rear of
potentiometer R32 is set between 10 to 30 seconds.
the receiver.
Note the delay setting.
(3) See that the remote alarm contact at TB1
(rear of unit) are properly wired for remote monitoring.
Terminals TB1 (5-4) are normally open (NO) contacts
Insufficient delay time setting by
and TB1 (4-3) normally closed (NC). If remote alarm
potentiometer R32 may result in a
indication is not required, do not use TB1 (3, 4, or 5).
false alarm condition. The minimum
(4) See that the 600-ohm audio line (if used) is
delay time must be greater then the
connected to TB1 (1-2).
time gap between normal keying
(5) Set power ON/OFF switch to OFF.
(6) Turn front panel latch and swing the front
pane open to the left.
(18) Set power ON/OFF switch to ON. This may
(7) Refer to figure 2-1 and determine the
result in an alarm condition after the time delay. Press
location of various adjustments and controls inside the
ALARM SIL switch to silence the aural alarm.
Familiarity with the location of these
(19) On switch bracket assembly, rotate RF
adjustments and controls will be helpful when performing
ATTEN switch counterclockwise, one step at a time, until
the following procedures.
the front panel CARRIER LEVEL meter shows a
(8) Locate the local oscillator crystal on the RF
deflection. Do not turn RF ATTEN control any further.
PCB and note its frequency, as marked on the crystal (it
(20) While observing the CARRIER LEVEL
is not necessary to remove crystal from PCB to read the
meter, slowly turn RF TUNE control for maximum
frequency marking). Add the frequency marked on the
deflection on the meter. Perform this step carefully so
crystal to the frequency of the NDB transmitter and note
as not to miss the maximum deflection point.
the sum. If the sum of the two frequencies is 4.4000
(21) On RF PCB adjust SENSITIVITY control R7
MHz, proceed with (15) below. If the sum of the two
to obtain a reading of 0 dB on the CARRIER LEVEL
frequencies is not 4.4000 MHz, proceed with (9) below.
(9) Determine the correct crystal frequency
using the following formula:
Crystal Frequency = 4.4 MHz minus the
In some cases it may be necessary to
transmitter frequency OR crystal frequency + transmitter
change the RF ATTEN setting by one
frequency = 4.4 MHz.
step to obtain the 0 dB reading
(10) Install the correct crystal on the RF PCB.
specified in(21) above.
(11) Connect a frequency counter to TP2 on the
RF PCB, using TP5 as the ground.
(22) On IF PCB, set CARRIER control R22 to the
(12) Set power ON/OFF switch to ON.  If the
required alarm trip level. For example, if the receiver is
audible alarm sounds, press ALARM SIL switch to
required to provide an alarm indication when the relative
silence the alarm.
carrier level drops by 3 dB, set R22 to 3 dB position.
(13) Observe the frequency counter reading; it
Note the setting of R22.
must be the same as the crystal frequency 10 Hz. If
(23) Check to see that the CARRIER LEVEL
necessary, adjust trimmer capacitor C13 on the RF PCB
meter reads 0 dB. On RF PCB, adjust the SENSITIVITY
until the frequency counter reading is within 10 Hz of the
control R7 to obtain a CARRIER LEVEL meter reading
crystal frequency. Trimmer capacitor C13 permits up to
of 1 dB below that noted in (22) above. For example, if
200 Hz adjustment in the crystal frequency.
CARRIER control R22 in (22) above was set at -3 dB,
(14) Disconnect frequency counter from TP2,
set SENSITIVITY control R7 to obtain a reading of -4 dB
and set power ON/OFF switch to OFF.
on the CARRIER LEVEL meter.
(15) On switch bracket assembly, set RF ATTEN
(24) Check to see that the receiver generates an
control to 80 dB position and RF TUNE control to the
alarm condition after the set time delay (ALARM light on,
appropriate operating frequency as described in table
NORM light off, and aural alarm on). Listen to the aural
alarm level. If the volume of aural alarm is too high or
(16) On RF PCB, turn SENSITIVITY control R7
too low, adjust potentiometer R13 on audio amplifier
fully clockwise (maximum sensitivity).
PCB for the desired tone volume. Do not adjust R13 if
(17) On IF PCB, turn TIME DELAY control R32
to any desired setting between 0 to 60 seconds. The

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