Radio Tuning Procedure
Maintenance 3-11
7.7 Rated Volume
The rated volume softpot sets the volume at normal test modulation.
1.
Set test box (GTF180) meter selection switch to the “AUDIO PA” position and the speaker load
switch to the "MAXAR" position. Connect an AC voltmeter to the test box meter port.
2.
From the Service menu, select Receiver Alignment.
3.
Select Rated Volume to open the rated volume tuning window. The screen will indicate the
receive test frequency to be used.
4.
Set the RF test generator to the receive test frequency, and set the RF level to 1mVolt
modulated with a 1 kHz tone at the normal test deviation shown in table 3-5. Set test box
(GTF180) audio switch to the “SPKR” position. The 1 kHz tone must be audible to make sure
the radio is receiving.
5.
Adjust the value of the softpot to obtain rated audio volume (as close to 3.87 Vrms).
6.
Click the Program button to store the softpot value.
7.8 Squelch
The squelch softpots set the signal to noise ratio at which the squelch opens. The squelch value
needs to be set at 7 frequencies across the frequency range.
1.
Set the test box (GTF180) meter selection switch to the "Audio PA" position and connect a
SINAD meter to the "METER" port.
2.
From the Service menu, select Receiver Alignment.
3.
Select Squelch Attenuation to open the squelch attenuation tuning window. The window will
indicate the receive test frequencies to be used.
4.
Select the first test frequency shown, and set the corresponding value to 0.
5.
Set the RF test generator to the test frequency and modulate the signal generator at the normal
test deviation shown in table 3-5, with 1 kHz tone. Adjust the generator for a 8-10 dB SINAD
level (weighted with psophometric filter).
6.
Adjust the softpot value until the squelch just closes.
7.
Monitor for squelch chatter; if chatter is present, repeat step 6.
Table 3-5
Normal Test Deviation.
Channel Spacing Deviation
12.5 kHz
20 kHz
25 kHz
1.5 kHz
2.4 kHz
3 kHz
Table 3-6
Start Value for Front-End Pre-selector Tuning.
RF-Band Target Stepsize Start Value
UHF
VHF
336-390MHz
0.5%
0.42%
0.84
-2
+2
-2
Maximum
Minimum
Maximum
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