Rated Volume - Motorola GM950E Service Manual

Radio Tuning Procedure
7.7

Rated Volume

The rated volume softpot sets the volume at normal test modulation.
1. Set test box (GTF180B) meter selection switch to the ÒAUDIO PAÓ position and the speaker
load switch to the ÒMAXARÓ position. Connect an AC voltmeter to the test box meter port.
2. From the Service menu, select Rx 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 1kHz tone at the normal test deviation shown in table 3-6. Set test box
(GTF180B) audio switch to the ÒSPKRÓ 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 3.74 Vrms)
Note: The voltage at the meter port of the testbox GTF180B is only half the voltage at the
speaker.
6. Press Program 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. For 20/25kHz radios, the radio stores
separate tuning data for 20kHz and 25kHz channel spacing. Therefore, both sets of tuning data
should be set independently.
1. Set the test box (GTF180B) meter selection switch to the ÒAudio PAÓ position and connect a
SINAD meter to the ÒMETERÓ port.
2. From the Service menu, select Rx Alignment.
3. Select ÔSquelchÕ 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 Þrst 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 3-6, with 1kHz tone. Adjust the generator for a 8-10 dB SINAD
level (weighted with psophometric Þlter).
3-12
Table 3-5 Start Value for Front-End Pre-selector Tuning.
RF-Band
UHF
VHF
Table 3-6 Normal Test Deviation.
Channel Spacing
12.5 kHz
20 kHz
25 kHz
Start Value
Maximum
Minimum
Deviation
1.5 kHz
2.4 kHz
3 kHz
Maintenance