A headset for the Elecraft K2
There are times when a headset - headphones with a boom microphone attached - is the most convenient way to operate using SSB. But ham radio headsets can be absurdly expensive, and are often uncomfortable to wear, like some World War 2 relic.
Previous attempts to find a headset that would work with my Elecraft K2 failed, due to the insensitivity of the K2's VOX (which the output from the headset mic was not enough to trigger) or because of RF feedback due to poorly screened leads. Elecraft itself offers the Proset-K2, an Elecraft-badged version of a Heil product, but that certainly fits my description of "absurdly expensive", while postings on the Elecraft mailing list suggest that it may not be immune to the problem of too-little audio output either.
I recently purchased a Plantronics Gamecom 1 headset, and I decided to try this with my K2. The Gamecom 1 is an attractively designed and comfortable headset. The headphones have good audio response. The microphone has a built-in muffler, and is easy to move into position, but when not required - for listening or when working CW - it folds up and out of the way.
There is a switch in the microphone lead, but this simply disconnects the microphone - it is not suitable for use as a press-to-talk switch. The headset is normally used in conjunction with the transceiver's VOX mode, so the switch is useful for muting the mic and preventing accidental triggering of the VOX.
Interfacing
The headset is equipped with two identical 3.5mm stereo jacks for connecting to a computer sound card. Learning from previous mistakes, in which I spoiled a headset by cutting off the microphone jack and connecting it directly to an 8-pin plug, only to find that it did not work satisfactorily with the K2, I used a line 3.5mm jack socket to make an adapter. This way, I could retain the use of the headset with a computer, perhaps for use with my remote control software K2Net.
My K2 microphone socket is wired to the Elecraft standard, so I connected the ground to pin 8 and the audio to pin 1. To help prevent RF feedback I also wired a 1nF capacitor across these two pins, to decouple any RF that might be present.
The microphone element in the Gamecom 1 is an electret type, so a DC bias is required. The K2 provides 5V output to pin 6 (assuming that you made this connection when building the transceiver) and so the bias is supplied via a 1/8 watt 3.3K resistor connected between pin 6 and pin 1. This value is not critical or even scientifically determined - it was simply the first one in this range that I found in the junk box!
The headset cable is very long, so I made an RF choke by tightly coiling several turns of the cable near the connector. I have to say that I didn't try to use the Plantronics headset without this RF choke or the decoupling capacitor, so I don't know whether they are actually necessary to prevent RF feedback into the radio, but previous experiences suggested that some attention to RF filtering would be a good idea.
Results
The results were extremely satisfactory. The headphones are comfortable to wear and provide very satisfactory listening. The microphone provides ample audio output to trigger the K2's VOX and deliver sufficient audio to fully drive the radio. The audio quality isn't quite as clear as when using my desk mic, but it is perfectly acceptable for contest or pile-up use - the typical situation for using a headset. I normally use most sensitive input setting and the 3:1 compression setting, giving the punchy audio that has always enabled the K2 to "punch above its weight" and get the kind of reports one would expect from a 100W rig.
Although I only operate at QRP power levels, with a maximum of 10 watts, I am using an indoor antenna farm located directly above the ceiling of my top-floor office /shack, so there is a lot of RF floating about. RF feedback has often been a problem with various items of equipment. However, after performing tests using 20m, 10m and 6m I could not detect any signs of RF interfering with the audio, with the headset connected as described.
Conclusion
The Plantronics Gamecom 1 makes a comfortable, attractive, effective and inexpensive headset for the Elecraft K2 transceiver. Doubtless it would work with other transceivers, and doubtless other good-quality computer headsets would work with the Elecraft K2, but a certain amount of luck may be needed to find one. Why pay three or four times as much for a "ham radio" headset when a readily available computer headset works just as well?
