TECHNISONIC INDUSTRIES LIMITED
www.til.ca
TFM-500 Installation & Operating Instructions
TiL 98RE243 Rev. N/C Issue 12
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 or 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 (2.5V RMS), 2.5 kHz audio signal into microphone
input 1.
4. Adjust the wideband deviation limit potentiometer, 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 potentiometer, 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.
6. Key the transmitter and input a +10 dBm (2.5 VRMS), 2.5 kHz audio signal into microphone
input 1 if in single mode or microphone input 2 if in dual mode.
