BULLETIN: PK0325 VENDOR: ICOM & KENWOOD SUBJECT: 9600 MODIFICATIONS FOR THE VARIOUS RADIOS ICOM: IC-290, IC-28, IC-3200 KENWOOD: TM-321, TM-421, TR-751 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, through a 680 ohm resistor. This one is my personal 2 meter 9600 rig, and works great! 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. Some rigs will require the transmit audio 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.