Maintenance GPH-CMD VHF Radio
Page 5-10 BK RADIO
H. Squelch
1. Squelch adjustment is a semi-automated process that must be performed in both
wideband and narrowband. The squelch adjustment is controlled using a digital
potentiometer U18 (Systems board).
2. Wideband Mode
With preset squelch (monitor/squelch control fully counterclockwise) the GPH-CMD
audio should turn on at approximately 8 dB SINAD. If components in the IF filter or
squelch filter are replaced, adjustment of the squelch may be necessary.
To perform the adjustment:
a) Program a receive frequency with no Code Guard, wideband (25/30 kHz) analog
mode. Turn the monitor/squelch control fully clockwise. Adjust the volume control
to mid range.
b) Connect an RF signal generator tuned to the programmed receive frequency to the
antenna jack of the radio. Modulate the generator with a 1 kHz tone at 3 kHz
deviation.
c) Connect a distortion analyzer to the radio speaker output.
d) Adjust the RF signal generator level to obtain an 8 dB SINAD reading on the
distortion analyzer.
e) Follow the instructions for Receiver Front End in the GPH-CMD Editor Software.
3. Narrowband Mode
This adjustment should always follow the wideband adjustment.
To perform the adjustment:
a) Program a receive frequency with no Code Guard, narrowband (12.5 kHz) analog
mode. Turn the monitor/squelch control fully clockwise. Adjust the volume control
to mid range.
b) Connect an RF signal generator tuned to the programmed receive frequency to the
antenna jack of the radio. Modulate the generator with a 1 kHz tone at 1.5 kHz
deviation.
c) Connect a distortion analyzer to the radio speaker output.
d) Adjust the RF signal generator level to obtain an 8 dB SINAD reading on the
distortion analyzer.
e) Follow the instructions for Receiver Front End in the GPH-CMD Editor Software.
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