BULLETIN: PK0400
VENDOR:   YAESU
SUBJECT:  9600 BAUD MODIFICATION FOR PACKET

Yaesu FT-207 9600:
      Discriminator output:  pin 9 of Q104.
      PTT connected to PTT switch.
      FSK input:  wiper of VR201.

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
                |       |   5-10K (approx - adjust for 3 KHz dev
                |       \         with modem's TXA pot about 50-75%)
          .001 ===      / 500 ohms
                |       \
                |       /
                |       |
               _|_     _|_
              ////    ////

If the transmit audio must be cut off during receive.
This is a simple circuit that'll do this.

+ 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.  The relay adds no measureable keyup delay.