PTT (Push to Talk/Transmit) Cable

AGWPE will generate the Transmit Audio, but you also need a way to open the radio's PTT circuit so that the audio can be transmitted. AGWPE and other sound card programs such as PSK31 provide for this by sending a signal to the RTS pin of the serial (COM) port or parallel (LPT) port on your computer. This gives you several options:

1. build a cable with an isolated 'gate' circuit that opens the radio's PTT circuit when it receives a signal from the RTS pin. You can use this cable on either your serial or parallel port.

2. use the cable above with a serial-to-USB port adapter to use your computer's USB port instead of the serial or parallel port.

3. use the voice activated (VOX) PTT circuits if your radio has one. If it works, you won't need a separate AGWPE-activated PTT cable. (Although you need to guard against room/computer noises if the VOX also opens the microphone.)

4. build a TX audio-activated circuit to achieve the result as #3.

A. Building A Cable With An Isolated Gate Circuit

You may find other variations of the circuit below, most commonly one using a standard transistor and a diode (in fact, there's one in the AGWPE 'Help' file). While these circuits will work, they create a direct electrical connection between the computer and radio, and thus create a risk of radio/computer damage in the event of different voltage potentials between the two components. For that reason, I don't recommend them.

Instead, I recommend an isolated 'gate' circuit. Here's a schematic for a single port (one Radio) AGWPE setup which uses a  phototransistor/opto-coupler as the gate: 

  <-- Click to enlarge

R1 = Resistor, e.g. 1K2, to reduce voltage on the IC pin 1
IC =  Integrated Circuit; this sketch shows an IC, such as a 4N33
        or PS2603 Optocoupler, which uses a Darlington pair transistor.
        (Note: to identify pin #1, look for a small embossed circle on
         the top of the IC above pin 1; or looking into the notch in one
         side of the IC with the pins down, pin #1 is to the right of the notch.)
D1 = Diode, e.g. IN4001, would shunt any potential reverse voltage
        that might damage the sensitive diode/emitter in the IC.
        (Note: the band printed on the diode marks the cathode end,
        which attaches to the Serial Port/IC Pin 1 line in the sketch above.
        The opposite/anode end attaches to Ground.)

The ideal components for your circuit may vary because of your radio's requirements. For example, you might be able to use a different type of IC, such as a 4N25 or PS2601, but that may require a different value for R1.