Adjustment Procedures.

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.

NOTE

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.

sequence.

(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.

receiver.

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.

meter.

(9) Determine the correct crystal frequency

using the following formula:

NOTE

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

2-2.

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

2-5