First I want to promote some excellent papers on rig interfacing and grounding produced by Jim Brown K9YC. There is a wealth of information there, produced by a very talented and experienced engineer.
- K9YC Publications web site
- Power, Grounding, Bonding, and Audio for Ham Radio
- Computer to Radio Interfacing…
- etc, etc.
Now…on to the topic of interfacing PC headset to ham rigs…
Heil Headsets get a lot of support and advertising in the amateur community. But they are expensive. The W2SZ VHF/UHF contest group that I belong to uses mostly Heil headsets, so I have a lot of experience with them. The problem is that a lot of them are broken. We only use them two weekends a year for about 36 hours but they fail in a variety of ways.
I don’t own a Heil headset (I’m too cheap), but wanted a more reliable headset for my own use on the mountain. In this case, reliable means I can bring several for a reasonable price. So, this led to a series of experiments with PC headsets that are available for prices that range from about $13 to $50.
PC headsets and Heil headsets operate differently. Heil headsets use a dynamic microphone and cannot tolerate any DC current through the microphone. PC headsets require a DC bias voltage to operate their electret microphone.
The diagrams below (copied from a great presentation on rig interfacing by AudioSystemGroup) shows the two ways a PC puts electret bias on the ring terminal of the 3.5 mm microphone jack.
All PC headsets have the ring terminal for bias…that is the key to this design.
The box below takes 8 volts from the ICOM microphone connector and uses it to power the PC headset. The circuit has…
- 3.5 mm (1/8th inch phone) jack for the microphone
- 0.47 uFd series cap on the microphone, pass audio and block DC
- 2.2K resistor to pass DC from the 8V pin to the ring terminal
- 1/4 inch phone jack for rig keying
- Cable and ICOM microphone plug
It was important to ensure the Heil headset doesn’t see any DC if plugged into the microphone jack of this adapter. The design put bias on the ring terminal to feed the PC headset. But, the Heil microphone connector does not have a ring terminal so it simply grounds the bias voltage… so, no bias gets to the Heil. The dynamic microphone in the Heil couples audio through the series cap.
Here’s another design. This one has two 3.5 mm connectors, one jack, one plug plus a battery. The battery supplies power to the PC headset without the need for power from the transceiver. This also supplies power to the ring terminal and block DC to the microphone on the tip terminal. This took about 5 minutes, the components are under the tape.
One of our W2SZ members, Tom Price KC2PSC, designed of a PC board to implement this idea.
- RJ-45 connector for rig microphone interface
- Converts to 3.5 mm microphone and line out
- Converts 1/4 inch phone for rig keying
- Includes option for battery
There are a number of web sites that discuss the same thing
