Running a TNC-2 clone at 19K
                ============================
 
The following is a relatively easy modification that allows reliable 19.2K
baud on the serial port and radio port of most TAPR TNC-2 boxes.

***** FIRST AND FOREMOST *****

Replace U3 (LM324 opamp) with a TL084CN or TL094 if no TL084CN or equivalent.
This is a high speed JFET hi-Z op amp.  Just that fix alone will allow you to
run 9600 baud on the serial port to your computer.  I found that the TAPR
1.1.6. code WITH the PMS ran without any serial port misbehaving BUT it was
sluggish.  The 1.1.6. code (or lower) without PMS is quite a bit quicker.

***** 19.2 K *****

Cut the PC trace that goes to pin 2 of divider U1 about 1/8" from U1. Run a
short jumper from pin 10 of the divider U1 to the side of the trace you just
cut that goes to the SW2 baud rate switch.  This is the side of the cut
opposite to pin 2 on U1.  This supplies a 307.2K clock to pin 1 and pin 6 of
the SW2 which NO LONGER SELECTS 300 BAUD.

The 307.2 K is 19.2K/16 which is fine and dandy.  To run 19.2K on the serial
port, turn SW2 switch 1 on.  SW2 switch 6 selects 19.2 K to the MODEM port,
switch 7 selects 1200 baud to the modem port and switch 8 selects 9600 baud
to the modem port.

(Keep in mind to leave switch 7 on unless you have installed a higher speed
modem in your TNC.)

We are running 19.2K serial and 9600 baud radio with G3RUH modems and
Kantronics DVR 2-2 radios with excellent results.  Next step is to up the
G3RUH boards to 19.2K by replacing a couple of capacitors.

Anthony Varga VE3ZAV

(Downloaded from GB7BBS)