From: LU7AKC@LU7AKC.#COL.CF.ARG.SOAM
To  : NET9K6@WW

 TM531<>G3RUH 9600bd
Hello, Ed.
I received your mail today morning,on Dec., 15.
I'm using TM-531 on G3RUH type 9600bps modem.
We ha local aria network using 9600bps modem.
It is working well,now.  But, beginning of this network is not easy.

You can connect G3RUH type modem as follow.

  1. TXA
   Take off the shielding plate under the main PCB.
   Search for VR3 on main PCB.
   VR3 is indicated on PCB "MAX DEV" for adjust maximum deviation.
   The slider of this VR is connected to MD pin of VCO through C55
   capacitor.
   Connect TXA to MD pin of VCO using resister(56k to 100kohm) and
   capacitor 0.1uF,connected in series,like follow.

     TXA ---II------/\/\/\----MD(VCO)
           0.1uF    56k to 100kohm

   If you get weary to take off shielding plate,you may connect the TXA
   to hot end of VR3, using the resister and capacitor as aforesaid.
TM-531 & 9600 Bps.

  2. RXA
    Search for IC2 on main PCB.
    IC2 is a 16 pin hybrid IC for IF AMP and discriminator.
    You can discriminate pin number of this IC from printed symbol on
    the main PCB, and grand pin.
    Pin 2 and 16 is connected to grand.
    pin 5 is output for ceramic filter(CF1),and pin 7 is input from the
    filter.
    Connect RXA to pin 12(DET) directly.

   9600bps on 1200MHz band is very difficult.
   Because,frequency stability is not enough.
   And, IF band width is not enough,too.
   We are developing SMC transceiver for G3RUH modem on 144,430,1200MHz
   band.
   It has high stability PLL OSC(about 1ppm) and good linearity
   modulator (voltage controlled X'tal OSC)

           Sammy JE1RLA @ JE1RLA
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