4          MODIFICATIONS

   There are some 9600 baud ready radios, like the TEKK KS-900, Kantronics 
DVR 2-2 (not recommended), and D410, but most of us will be using our
existing 
radios for 9600 baud packet.  Here are some specific "mods" and tips.

     Radios known to be used at 9600:
Alinco: DR-1200 DataRadio, ALR-72, ALR 709; Kantronics DVR 2-2 Data Radio; 
Icom IC series: 25,38,228,271,290,471; Kenwood TR series: 7500, 7700; 
TM series: 211,212,221,231,431, TS series: 700 and 770
Standard C58, C140; Yaesu FT series: 212,221,230

4.1        RADIO

4.1.1      TEKK KS-900

   For the TEKK KS-900, a TXAudio attenuator is necessary to swamp the
modem's 4 volts peak to peak down to the 50 mV range.  

   This is simply a 470 ohm resistor in series, and a 39 ohm resistor across 
the TEKK's transmit input and ground.

4.1.2      OTHER RIGS

   It's almost embarassing to call these "mods".  We're only bringing out 
terminations of existing signals.

   These mods are non-destructive unless you QSLF (solder with your left 
foot :-) - your rig still does whatever it did before.

   Icom IC290H/V: RXA may be obtained at IC12, pin 9, on the main board; 
TXA may be injected at D-3 cathode on the main board  (This one is my 
personal 2 meter 9600 rig, and is a top performer!)

   Icom IC28A/E/H : RXA may be obtained at IC1, pin 9, on the RF unit; 
TXA may be injected at R-45, at the end NOT connected to trimpot R-100

   Icom IC3200A/E: RXA may be obtained at IC1 pin 9 (main board) - this is a 
common receiver chip for both bands; TXA may be injected at D3 cathode (VHF) 
and D1 cathode (UHF).

   Kenwood TM221, TM321A, TM421: RXA may be obtained at IC1, pin 9 (IF
board); TXA may be injected at connection #7 on the VCO assembly on the TX/RX
unit.

   TR751: RXA may be obtained at IC2,pin 9 on the RX unit; 
TXA may be injected at D21 cathode on RX unit.

   Use the following circuit to couple the modem to the radio.

MODEM                            RADIO
      5 - 10 MF non-polarized
RXA ----||----------------------------- RXA
     
      5 - 10 MF non-polarized
TXA ----||------o-------o---/\/\/\----- TXA
                |       |    10K (approx - adjust for 3 KHz dev
                |       \         with modem's TXA pot about 75%)
          .001 ===      / 500 ohms
                |       \
                |       /
                |       |
               _|_     _|_
              ////    ////


4.1.1      TXA CUTOFF

   If you want to leave your 9600 connected and use the rig for other stuff, 
use the following relay circuit:

+ 12 VDC----------------o     o--->|<------------- Radio PTT
                        |     |   N.O.
                       _|_    |
                      |   |  _|_
                      |RY1| ////
                      |   |
                      |___|   o--->|<------------ Radio TXA
                        |     |   N.O.
TNC PTT ----------------o     |
                              |
Modem TXA --------------------o

RY1 is a double pole 12 volt relay.  Use the normally open contacts

   This removes the modems TXAudio line from the radio's modulator when
you're not keying from the 9600 baud TNC.  If you're using the same TNC for
1200 and 9600, make sure you remove the PTT signal from the relay!  Otherwise
you'll pick up a nice 4800 Hz "tone" from the 9600 band modem.