Squelch; Transmit Voltage Limit; Transmit Deviation Balance (Compensation) - Motorola GM1200E Service Manual

GM1200E Tuning Procedure
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.
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 4-3, 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.
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.
1.9

Transmit Voltage Limit

The transmit control voltage limit softpot sets the maximum power control voltage. All 7 voltage limit
softpots are tuned and programmed automatically when the Program button is clicked.
1. From the Service menu, select Transmitter Alignment.
2. Select Voltage Limit to open the voltage limit tuning window.
3. Set the Power Factor to 1.3.
4. Click the Program button to store the softpot values.
1.10

Transmit Deviation Balance (Compensation)

Compensation alignment balances the modulation sensitivity of the VCO and reference modulation
(synthesiser low frequency port) lines. Compensation algorithm is critical to the operation of
signalling schemes that have very low frequency components (e.g. DPL) and could result in
distorted waveforms if improperly adjusted. The compensation value needs to be set at 7
frequencies across the frequency range.
1. From the Service menu, select Transmitter Alignment.
2. Select Modulation Attenuation to open the deviation balance tuning window. The window will
indicate the transmit test frequencies to be used.
3. Set the Test Box (GTF180) meter selector switch to the "GEN" position, and inject a 80 Hz tone
at 200 mVrms into the "Audio In" port. (The deviation measured at step 6 should be about
1-4kHz.) Connect an AC meter to the meter port to insure the proper input signal level.
4. Select the first test frequency shown in the window.
5. Click Toggle PTT to key the radio. The status bar will indicate that the radio is transmitting.
6. Measure the transmitter deviation.
4-6 Radio Tuning Procedure