User's Manual

3-9
3.11 SQUELCH ADJUSTMENT
The squelch circuit is designed to open or close depending upon the noise content and not
the strength of the received signal. Therefore high squelch settings are not necessary nor
possible. The squelch on both the VHF and UHF receivers is factory set to open at
approximately 22 dB SINAD, while the guard receiver is set to open at 25 dB SINAD. The
range of adjustability is approximately 3 to 27 dB SINAD. This adjustment can be made or
altered to suit local conditions as follows:
1. Set the receiver to 157.000 MHz for VHF or 457.000 MHz for UHF. Connect a signal
generator to the antenna input of the desired band.
2. Set the signal generator to produce a ±3 kHz deviation with a 1 kHz tone on 157.000
MHz or 457.000 MHz. Increase the signal generator RF level from 0 uV until the
squelch indicator LED is on. Verify the squelch opens at the desired level.
3. If not, re-adjust receiver squelch potentiometer through the access hole located on the
bottom or side of the transceiver chassis (see Figure 3-4).
3.12 TRANSMITTER DEVIATION ADJUSTMENT
VHF:
1. Remove the bottom cover of the transceiver.
2. Set the VHF operating frequency to 157.000 MHz and connect an appropriate test
receiver to the RF output connector. Ensure that the output of the transceiver is
terminated into a proper dummy load.
3. Key the transmitter and input a +10 dBm (2.5 VRMS), 2.5 kHz audio signal into
microphone input 1.
4. Adjust the wideband deviation limit potentimeter, R30 on the VHF Rx/Tx module (see
Figure 3-5) to produce a ±4.25 kHz deviation. Select narrow band mode on the VHF
band and adjust the narrowband deviation limit potentimeter, R76 on the VHF Rx/Tx
module to produce a ±2.15 kHz deviation.
5. Verify that the deviation does not exceed ±5 kHz for wideband and ±2.5 kHz for
narrowband on 138.000 MHz, and 174.000 MHz. Re-adjust R30 or R76 as required,
if the deviation exceeds ±5 kHz or ±2.5 kHz, respectively.
6. Replace the bottom cover.
UHF:
1. Remove the top cover of the transceiver.
2. Unplug the white coax from the guard receiver and remove the front panel.
3. Remove the guard receiver tray.
4. Replace the front panel and select the UHF band.
5. Set the UHF operating frequency to 457.000 MHz and connect an appropriate test
receiver to the RF output connector. Ensure that the output of the transceiver is
terminated into a proper dummy load.