HM135 Service Manual
Preliminary version Page 13 of 13
3.10 Setting of the Squelch Level.
1) Switch the radio to CH2, 155.100 MHz.
2) Turn RP1, SQUELCH LEVEL ADJ, until radio opens without signal applied to the antenna input.
3) Connect a SINAD meter to pin 5 of rear DB25 connector. Switch off the CCITT filter the SINAD meter. Connect a RF
generator, tuned to 155.100 MHz to the radio’s antenna connector
4) Set the RF generator modulation frequency to 1kHz and the deviation to 3 KHz. Set the RF output of the generator to –87
dBm (10 uV).
5) Decrease the level of RF generator until SINAD meter reads approx 8 to 9 dB. Note the RF generator settings.
6) Decrease the RF generator level with 6 dB. Turn slowly RP1, until the squelch close.
7) Increase the level of RF generator slowly until Squelch opens. Note the RF level. It must be approx the same, as set in step
5 above. If not, set the level to the same, noted in step 5 and repeat the settings of RP1 again.
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