Transmit Modulation Balance (Compensation); Transmit Deviation Limit - Motorola GM-950 Manual

1.9

Transmit Modulation Balance (Compensation)

Compensation alignment balances the modulation sensitivity of the VCO and reference modulation
(synthesizer 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. If the radio supports 20 or 25 kHz channel spacing
selection, the procedure must only be performed for 25 kHz channel spacing. Values for 20 kHz
channel spacing are calculated by the radio software.
1. From the Service menu, select Tx Alignments.
2. Select 'Modulation Balance' 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 in the
range of 1-4 kHz.) 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 the Toggle PTT button to key the radio. The status bar will indicate that the radio is
transmitting.
6. Measure the transmitter deviation.
7. Change the input tone to 3 kHz, 200 mVrms.
Adjust the deviation to within ±2% of the value recorded in step 6.
8.
9. Check the deviation at 80 Hz again and repeat steps 7 - 8, if it has changed since step 6.
10. Click the Toggle PTT button to dekey the radio.
11. Repeat steps 3 - 10 for the remaining test frequencies.
12. Click the Program button to store the softpot values.
Note: The step size change for step 8 is approximately 2.5% of the softpot value.
1.10

Transmit Deviation Limit

The transmit deviation limit softpot sets the maximum deviation of the carrier. The deviation value
needs to be set at 7 frequencies across the frequency range. If the radio supports 20 or 25 kHz
channel spacing selection, the procedure must only be performed for 25 kHz channel spacing.
Values for 20 kHz channel spacing are calculated by the radio software.
1. From the Service menu, select Tx Alignments.
2. Select Deviation Limit to open the deviation limit tuning window. This window is used to set the
values for 12.5 kHz radios and the 25 kHz data for 20/25 kHz radios. 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 1 kHz tone
at 800 mVrms into the "Audio In" port. 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 the Toggle PTT button to key the radio. The status bar will indicate that the radio is
transmitting.
6. Adjust the transmitter deviation to the value shown in table 2-5.
Radio Tuning Procedure
Midband (66-88MHz) Tuning Procedure
5C.2-7