This page is a collection of information on the AWA RT85A
FM mobile transceiver.
Most of this information applies specifically to the UHF low band units that were used by the Royal District Nursing Service, Melbourne, Australia, and found their way into the amateur service around January 2002.
The A version is different to the standard RT85 and the C models.
These instructions assume a reasonable level of technical competance and familiarity with radio tuneup proceedures.
Use this information with care, and always use the correct tools!
3/. Replace the EPROM with a new version with Amateur frequencies programmed.
(pry it out of the socket with a small flat blade screwdriver under each end of the EPROM, being careful not to bend anything.
Be very careful not to bend the pins when replacing the EPROM).
5/. With a fine screwdriver, screw the receive (L702) and transmit (L107) VCO slugs all the way in (so they bottom) - don't work about breaking these - they are metal.
6/. Connect up the control head, power supply and a dummy load again.
7/. Turn on radio. Select a channel in the middle of the desired frequency
range. The radio will beep continuously if the PLL is unlocked.
Tuning the VCO should stop the beeping.
Connect a volt meter to Rx VCO test point TP701 (top left corner - large silver pin). It should measure about 3.5 Volts but his is not critical. Now select the lowest frequency channel - check the voltage does not fall below 1.7 Volts. Select the highest frequency. Check the voltage is below 6 volts. If not, adjust L702 for the best compomise around 3.5 Volts.
(The VCO is quite broad and can tune at least 15 MHz).
8/. Repeat step 7, but this time for the transmit VCO adjusting L107
while measuring TP101 (right hand side, mid way between tin cans).
Push the microphone PTT while doing this!.
9/. If you have a suitable connector, connect a power meter where the
PA coax was unplugged( J366, top right corner). While pressing PTT,
adjust trimmer CV102 with an insulated tuning tool for maximum output (about
500mW - 1.2 W).
If a power meter cannot be connected, just follow the next step and tune CV102 for maximum output.
10/. Connect the PA coax back into J366.
Connect a 10 Amp ampmeter in the main 13.8Volt supply line.
Rotate RV501 & RV502 fully clockwise.
11/. Select a Press PTT and adjust trimmers CV501 then CV504 then CV502
and finally CV503 for maximum output power.
Tweak CV102 if necessary. Repeat adjustments for maximum power. Power out should be around 20 to 25 Watts.
You may find that CV501 & CV504 have little effect on second adjustment - Try detuning CV102 so the output power is around 15 Watts, this will make peaking CV501, CV504, CV502 & CV503 easier. Finally reset CV102 to original position.
With careful adjustment you will find that slight detuning of CV504, CV502 & CV503 results in lower current consumption.
Avoid tuning points where the transmitter "takes off" - observable as spots where power output rises and falls rapidly when rotating trimmers through their peaks.
Check power output and current consumption across all channels. Retune for best compromise if necessary.
12/. Adjust output power with RV502. Set output slightly
lower than required as the output power rises with temperature. Either
adjust so that power is reduced slightly on all channels (if you want to
live dangerously!), or reduce to a more conservative value (say 20 Watts
- for a longer PA life!).
Check output across all channels, Current consumption should be under about 5.5 Amps at 20 Watts. Efficiency falls off rapidly at higher power and just creates a lot of heat so keep current under 6 Amps.
13/. Select low power by linking P302 to P303 on back of head. Adjust
output to desired low power level with trimmer RV501 (say 3 to 5 Watts).
Do not adjust too low as this adjustment changes with temperature and may
turn off output completely in cold temperatures.
15/. If this is an unmodified district nursing service radio, start by unscrew (anti-clockwise) all the helical resonator adjustment screws by 2 turns each (L201, L202, L203, L204, L205 & L206 are metal screws on diecast housings). This gets the tuning into the right ball-park for 70cm.
16/. Turn on radio and select mid-frequency channel.
Connect voltmeter to LO buffer between test point pin 4 and pin 1 on connector CM202 (connect located near left hand side. White plastic header with 4 pin positions, pin 2 is the missing pin).
Adjust trimmers CV202 & 203 for maximum reading.
17/. With suitable signal source at input, connect meter between pin
3 and pin1 of connector CM202. Positive goes to pin 3.
The RT85A is relatively narrow banded ~2 MHz and can be tuned for maximum sensitivity if all channels are within this band as follws: Adjust all helicals (L201 to L206) for maximum reading. Reduce signal source level as you go so signal is reasonably noisy when making adjustments. Also adjust CV202 and CV203. Repeat several times.
Maximum bandwidth can be achieved by stagger tuning the helical resonators.
Try the following for a reasonable compromise with good sensitivity in
the 438-440MHz range (repeater outputs & high end simplex) and acceptable
but poorer sensitivity in the 433-435 MHz range (repeater reverse and low
simplex band): First select a channel near 439 MHz and adjust L201,
L202, L205 & L206 for best sensitivity. Also adjust CV202 &
CV203 at this frequency. Then select a channel near 435 MHz and adjust
L203 & L204. There is some interaction, so repeat the tuneup
cycle for 439 and 435 MHz several times.
The lower frequencies will be a few S-points lower than the higher channels.
18/. Finally connect an antenna and try an on-air test. Receive performance should be similar to most amateur transceivers of a similar vintage.
AWA RT85A personality data (configuration bits)