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Transient Protection Circuit Test |
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 SB 740-91-01
Step
Setting and Instructions
Normal Indication
5
(b)
Refer to figure B-18 and connect the
The modulation meter shall
(cont.)
equipment as shown. Set the function
read between 80 percent to
switch on the control unit to T/R+G posi-
95 percent. If the modula-
tion and allow the equipment to warm up
tion meter does not read
for at least 5 minutes. Adjust the audio
these percentages adjust A4P1
oscillator for an output of 1000 Hz and a
on the modulator and audio
signal level of 0.8 volts. With the con-
module for approximately 85
trol head frequency set at 304.7 MHz, key
percent modulation.
the transmitter by operating the CW
switch.
6
Transient Protection Circuit Test
To check the transient protection
If it lugs, the transient
circuit when testing the RT-742B/ARC-
protection circuit is good.
51BX, connect a 1 to 1.5k ohms, 1-watt
If it does not, reject the
resistor from ground to the top of the
radio set as Q is shorted.
power diode CR2, main frame, under the
power amplifier and listen for the
sound of the blower motor lugging.
7
Receiver Tests
otherwise specified herein, the
receiver tests shall include those to be
made at approximately each of the extreme
and midpoint frequencies available and
also the guard channel frequency. All
tests should be made using manual control
C-4677/ARC-51X, or preset to the T/R+G
position and give at least a 5 minute
warm-up period. With the equipment
connected as shown in figure B-20 the
following alignment procedure will be
used when bench testing the RT-742B/
ARC-51BX.
(a) Adjust the signal generator for a
The audio level for the main
1,000 microvolt input modulated 30
receiver is now set.
percent at 1,000 Hz. With a frequency
of 304 MHz, adjust A4R21 on the audio
modulator for 100 milliwatts output
across 150 ohms impedance.
(b) Adjust the signal generator for
Squelch level of the main
1.5 to 2 microvolts output modulated
receiver is now set.
30 percent at 1,000 Hz and re-peak the
generator to 304.7 MHz. Slowly turn
A3R50 on 3rd IF amplifier until squelch
opens (threshold).
B-79
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