An Extension Box For The IC-706MkIIG

An Extension for Your Radio

Geoff Haines, N1GY

Every once in a while, I come across a reason to build a specific piece of gear for a specific purpose that seems to suddenly be applicable to all kinds of other situations that I didn’t even think would apply. The little gadget described here fits that mold.

I needed a kind of extension to allow me to operate the radio in my car from a position outside the car. Specifically, I needed to be near to but outside the car to see and log participants in a charity bike race/tour as they went by my checkpoint, but I also needed to report their progress back to net control. Ordinarily, I would just use my hand-held to do this, but in this particular instance, the HT did not have enough power to reliably hit the repeater. Since I knew that this would mean a lot of running back and forth to the car, and the possibility of missing some of the riders, I put some of those little grey cells to work on the problem.

I had previously discovered that I could easily operate a headset with PTT over 15 feet away from the Icom IC-706MkIIG in my house, using standard CAT-5 cables as extensions from the mic connector on the radio. This meant that I could go at least that far away from the car and still be able to control the PTT and the UP and Down switches on the mic. An external speaker would provide the received audio. With a simple switch or even one of those audio jacks that automatically route the audio to the external speaker when it is plugged in, I could also use a headset if need be. The only real question was how do I package it all so it is easy to set up?

The answer came while I was looking at another project of mine, an ON-AIR sign I had made from a VHS Video Cassette Box. You know, the kind that is made out of plastic and has a folding lid that snaps shut. I could mount an external speaker, scrounged from an old computer speaker set in the top. Along the side of the box, I could mount the CAT-5 female connector for the mic and a 1/8” stereo jack for the headset or earphones. Because I did not have one of those slick audio jacks available that I mentioned before, I used a SPDT switch to route the audio to the speaker or the earphone jack. I was even able to re-cycle the speaker grille from the PC speaker set to cover the external speaker and make it look neat.

The upshot of all this puttering about is that I can now sit in a comfortable chair watching the race, with a small box on the table beside me that contains all the vital controls to operate the radio in the car. I have not determined what the longest distance is that I could extend the controls to, but for now 15 feet seems fine. All of the functions that are available on the stock hand mic are functional and the external speaker delivers great audio to my position outside the car.

If you wish to experiment with extending the distance further, my suggestion would be to add more CAT-5 patch cables and double female RJ-45 splice blocks and have at it. You will know when you have extended it too far, it will cease to work properly. Back up one patch cord and you will know what the maximum extension distance is.

I mentioned at the beginning that it has more uses than just what it was originally designed for. I can also use it to operate my base station from outside the room where my station is sited. Yup, there I am outside on the patio talking on the radio which is inside the room. I can enjoy the pleasant evening outside while still using the radio, without having to haul the radio outside too.

The same idea could be applied to an Emergency Operations Center where desk space is limited. Mount the radio under or inside the desk and just bring out the extension box for the mic with its external speaker. EOC radio setups usually do not have to change frequency often anyway. The radio is secure against being knocked off the desk by an errant elbow and yet the mic and the audio are close at hand.

I am sure you can come up with other situations where a mic/speaker extension could be of use. For now, just keep on building stuff, that’s one of the things that makes amateur radio so enjoyable.