Rated Volume; Squelch - Motorola GM950E Service Manual

216-246MHz Tuning Procedure
1.7

Rated Volume

The rated volume softpot sets the maximum 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 Rx Alignments.
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 1kHz tone at the normal test deviation shown in table 6.2-3. Set test box
(GTF180) audio switch to the "SPKR" position. The 1kHz 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)
Note: The voltage at the meter port of the testbox GTF180 is only half the voltage at the
speaker.
6. Click the Program to store the softpot value.
1.8

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. If the radio supports 20 or 25 kHz
channel spacing selection, the radio stores separate tuning data for 20 kHz and 25 kHz channel
spacing. Therefore, both sets of tuning data should be tuned independently.
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 Rx Alignments.
3. Select 'Squelch' to open the squelch tuning window. This window is used to set the values for
12.5kHz radios and the 25kHz data for 20/25kHz radios. 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 6.2-3, with 1kHz 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.
8. When no chatter is detected, select the next softpot and repeat steps 4 - 7 for all test
frequencies shown in the window.
9. Click the Program button to store the softpot values.
10. If the radio supports 20 or 25kHz channel spacing selection, repeat steps 2-9 for 20kHz
channel spacing using the 'Squelch (20kHz)' window.
6.2-6 Radio Tuning Procedure