TECHNICAL MANUAL FOR COMPACT VHF DSC RM2042

3 SERVICE RM2042ADJUSTMENT OF TRIGGER LEVEL FOR CHANNEL-70 CARRIER DETECTThe channel-70 carrier detect circuit is constructed as a noise triggered squelch and the trigger level isadjusted by the trimming resistor R36-3.1. Apply an unmodulated carrier with the frequncy 156.525 MHz to the antenna terminal and adjustthe output level of the RF-signal generator to -126 dBm (EMF: -13 dB/µV).2. Connect a multimeter or an oscilloscope to the output of the voltage comparator, pin 14 at U4.3-3, for measuring the DC-voltage.3. Turn the trimpot R36-3 counter clockwise until the output goes high.4. Increase the RF-input level to -125 dBm (EMF: -12 dB/µV).5. Now adjust R36-3 clockwise until the output goes low.6. Increase the RF-input level to -122 dBm (EMF: -9 dB/µV) and control that the output goes high.ADJUSTMENT OF TRIGGER LEVEL FOR VHF CARRIER DETECTThe VHF carrier detect circuit is identical to the corresponding carrier detect circuit for the build-inchannel-70 receiver and the trigger level is adjusted by the trimming resistor R93-3.1. Connect the RM2042 to the VHF tranceiver by means of the 9 pole SUB-D connector.2. Apply an unmodulated carrier with the frequncy 156.525 MHz to the antenna terminal at theconnected VHF tranceiver and adjust the output level of the RF-signal generator to -126 dBm(EMF: -13 dB/µV).3. Connect a multimeter or an oscilloscope to the output of the voltage comparator, pin 13 at U4.4-3, for measuring the DC-voltage.4. Turn the trimpot R93-3 counter clockwise until the output goes high.5. Increase the RF-input level to -125 dBm (EMF: -12 dB/µV).6. Now adjust R93-3 clockwise until the output goes low.7. Increase the RF-input level to -122 dBm (EMF: -9 dB/µV) and control that the output goes high.ADJUSTMENT OF 10VThe 10V power supply is used by the build-in channel-70 receiver and the FSK encoder/decoder.1. Connect a voltmeter to the output of the 10V power regulator, pin 1 at U10-3.2. Adjust the DC voltage to 10V ±10mV.3.7 REPLACEMENT OF COMPONENTSWhen replacing integreted circuits, transistors, diodes, resistors, capacitors and similar components youmust use a small “pencil” soldering iron with a maximum temperature of 300°C (572°F). The soilderingmust be performed rapidly to avoid superheating and the use of a desoldering wire is recommended, asotherwise there is a risk that both the components and the printed circuit will be spoiled.3.8 REPLACEMENT OF MODULESIf a fault has been located to a single module, it may often be worth-while to replace it and then repair itlater on.9403PAGE 3-9