[ICOM] Digital Interface Problems

[gfiber at comcast.net]

Bob,

The PTT line is unlikely causing the issue. Its the high impedance audio input in the back of the rig. Any noise that gets onto the cable running into that input will get into the radio. Sometimes ferrite beads will do the trick. You might have a ground loop so the addition of a transformer into the audio line will help.The mic being connected is secondary to this issue. The real culprit generally is RF floating about the shack. This will cause distortion every time. I have seen it many times with AFSK setups for packet and PSK31. You might have some luck with by establishing a better RF ground system. But I think the addition of a transformer will do as well. I would think you are likely getting the distortion when operating digital modes too. Others here may also have some Ideas to tell you about.

For the mic being left connected, I don't remember much about the EX-1514 but seems to me you could use it for either VOX or PTT. If I am correct then every time you key the radio in Voice mode the mic element is working. So far as I remember none of Icom's mics ever switched the mic audio lead through the PTT switch. It the PTT did switch the mic audio then you would need to make sure it was closed to run VOX. Really it may not be much of an issue leaving the mic connected. It is not likely causing the distortion you are experiencing. But just the same you do need to be aware that the element is operational every time the PTT line is operated in Voice mode no matter when keyed from the mic or rear panel of the radio.

Gary K8IZ