FT-817 Data Interface

In the spring of 2008, I became the proud owner of a brand new FT-817ND purchased from AES.  I wanted a rig that would interface with my HP iPAQ rz1715 and the fantastic Open Source digital application PocketDigi for portable/bicycle mobile operations.  I have not been disappointed!

There are two problems with the iPAQ rz1715 when it comes to interfacing it to the radio:

  1 - There is no direct input to feed the received audio

  2 - PTT is difficult to achieve via the fragile serial connector

The first point is easy to "solve" by just using the built-in microphone.  The AGC seems to work quite well by placing the top of the iPAQ near the FT-817 speaker.  Normal background noise has little, if any effect, on all but the weakest signals.

The second point is a little harder to solve.  I pondered this issue for a number of days, and finally decided to build a circuit to trigger the PTT from the transmit audio.  The circuit is actually quite simple and inexpensive to build.

The value of C1 will directly affect the sensitivity and hang time of the PTT.  There is also some interaction with the sensitivity and the output frequency.  This is not normally an issue as long as you keep your output audio frequency above 1 KHz.

If you are careful and choose your parts carefully, you can place all of the circuitry within the mini-DIN connector.  Surface mounted components work quite well in this case, making for a very compact interface.

One minor issue with this circuit is that the PTT will sometimes trigger when the interface is first connected to the FT-817.  This is easy to "fix" by just transmitting a tone for a second or two.  I do this with the radio set to the FM broadcast band.  The rig will beep for a second while the PTT is active, but no harm will come to anything.