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RT-85

Sat, 19/09/2009 - 20:18 — VK2VSV

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

REPROGRAMMING THE EPROM

Either, we can programme your EPROM for you with
OUR channels, or, you are on your own.

The RX VCO.



  • Add lOp to C709.

TX VCO.



  • Add lOp to C137

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

Our Channels are

Ch
Rpt Rx

Ch
Rpt Rx

1
53.550
19

52.550

2
53.575
20
52.575

3
53.600
21
52.600

4

53.625
22
52.625

5
53.650

23
52.650

6
53.675
24

52.675

7
53.700
25
52.700

8
53.725
26
52.725

9

53.750
27
52.750

10
53.775

28
52.775

11
53.800
29

52.800

12
53.825
30
52.825

13
53.850
31
52.850

14

53.875
32
52.875

15
53.900

33
52.900

16
53.925
34

52.925

17
53.950
35
52.950

18
53.975
36
52.975

Ch
Simplex
Ch
Simplex

37
52.500
55
53.400

38

52.525
56
53.425

39
53.000

57
53.450

40
53.025
58

53.475

41
53.050
59
53.500

42
53.075
60
53.525

43

53.100
 
 

44
53.125
 

 

45
53.150
 
 

46

53.175
 
 

47
53.200
 

 

48
53.225
 
 

49

53.250
 
 

50
53.275
 

 

51
53.300
 
 

52

53.325
 
 

53
53.350
 

 

54
53.375
 
 
Roger Baker VK3BKR and Mark Detering VK3TLW