Parts List

VHF Amplifier Instruction Manual VT-3 132 - 174 MHz 3-5
3.6.2.3 Output Power
1. Turn R7, the output power adjustm ent, clockwise to the desired transmitter output
power.
3.6.2.4 Antenna VSWR Alarm (Reverse Power)
Open Collector Output
* note: the antenna VSWR alarm output is factory configured as an open collector
output so a pull-up resistor may be required on transmitter pin Z26 if one is not
already present. The output power alarm must be set first before the antenna VSWR
alarm can be set.
1. Disconnect the radio communications test and terminate the transmitter with the 3:1
mismatch load.
2. Monitor pin Z26, the Antenna VSWR Alarm line, and turn R36 fully
counterclockwise. Pin Z26 should be high. Slowly turn R36 clockwise until pin Z26
is pulled low. Put the 50 ohm load back on again, Pin Z26 should go high. The
reverse power trip point is now set for a VSWR of 3:1.
Linear Output
1. Open the amplifier case to disable (open circuit) jumper JU3 and enable (short)
jumper JU4.
2. Monitor transmitter pin Z26 with a voltmeter.
3. Disconnect the radio communications test set and terminate the transmitter with the
3:1 mismatch load.
4. Adjust R36, the VSWR alarm adjustment, so that the voltmeter indicates +5 Vdc for a
3:1 mismatch.
5. Put the 50 ohm load back on again. The voltmeter should read approximately 0 Vdc.
6. Disconnect the voltmeter.