Converting an AWA RT85 LOW BAND Transceiver
to 6 Metres
by Roger Baker VK3BKR and Mark Detering VK3TLW
Notes apply to the RT85. NOT the RT85A,B, or C
The RX VCO.
TX VCO.
The EXCITER
- Remove original L114 and keep (for use in PA Board); replace with 7.5 turns O.5mm wire
The RECEIVER
- Add lOp to C202
- Add 22p to C205.
- Add 22p to C208.
- Add 22p to C212.
- Add 4p7 to C220.
P.A. BOARD.
- Add 22p to C512.
- Remove original L501 and keep; replace with original L114 (fom the Exiter board)
- Remove original L503 and keep; replace with original L501.
- Remove original L507 and replace with original L503.
- Remove original L513 and keep, replace with 2.5 turns 1.25mm wire.
- Remove original L512 and replace with original L513.
RX VCO
- The RX VCO will probably be out of lock when the radio is first powered up. The display will show "95" and the speaker will beep.
- Connect a multimeter to TP701 and adjust for approximately 4.7 volts. It should now be possible to change channels up and down.
- Set the radio to Channel 18 (53.975MHz highest Rx), and adjust L701 for 4.70 volts.
- Set the radio to channel 37 (52.500MHz lowest Rx) and check that the voltage is NOT less than 1.6 volts.
TX VCO
- Set the radio to channel 36 (53.975 MHz highest Tx) and connect a multimeter to TPl0l. Operate the PTT and adjust L107 for 4.70 volts.
- Set the radio to channel 37 (52.500 MHz lowest Tx) and operate the PTT and check that the voltage is NOT less than 1.6 volts
LO Injection
- Connect a multimeter to pin 4 on CM202 on the Receiver board. Adjust L209 and L210 for maximum indication on the meter (about 0.5 volts).
RX Tuning
- Using a suitable signal source, adjust the RX front end slugs for best bandpass
TX Tuning
- Connect multimeter to TP101 and adjust L107 for 3.5v on a centre channel
- Adjust CV102 for max RF output
- Set RV502 to fully clockwise position
- Adjust CV501, 502 AND 503 for Maximum Power output
- Re-adjust RV502 for approx 25W (or slightly less than whatever power is attained in the previous step as this enables your PA protection circuitry).
- Set Deviation at 4.5khz using RV501
- L101 and L102 may be adjusted slightly to give deviation symmetry
These mods should result in the receiver having a sensitivity of approx 0.25uV and a Tx power of at least 25Watts
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