KFRT's SOxR
Single Operator Multiple Radio Interface


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One of the fun things about amateur radio is that it's a great excuse to buy all sorts of equipment. Most hams who have been around awhile and are active have more than one radio. This is never a problem because more rigs means more fun!

In a fixed station installation, multiple rigs can be a slight issue because we don't generally want to assemble a number of complete stations, each with its own microphone, key, etc. Or maybe we do, but play along here, okay?

Contesters have been using SO2R (Single Operator, 2 Radio) interfaces for some time. This allows the operator to quickly switch from using one radio to using another almost instantly. The microphone and key stay the same and in essance, the SO2R box is a way to electrically swap radios at the flick of a switch. Some of the commercial solutions to this are elaborate and expensive! Of course, I'm just a contest hacker with a limited budget, but it's still a minor problem looking for a major solution.

It seemed to me that this might be pretty easy to homebrew. Of course, this is a custom solution for my own situation, but it's probably adaptable to your own station. Part one of this project concentrates on phone and CW modes.


First off, the equipment to be interfaced: I have my Kenwood TS-570SG, an Icom IC-7000, a Drake 4C line (separates) plus a Drake TR-4C. This is an intersting mix for the project because the Drake stuff uses low-impedance microphones and grid-block keying while the modern gear uses high-impedance audio and logic-level keying. In addition, the newer rigs both have keyers while the Drake stuff requires an external keyer (or you use a bug or straight key).

The goal will be to use all four rigs, so SOxR instead of SO2R. With the right switches, this could be adapted to almost any number, but 4 seems reasonable for now.

The microphone impedance problem is easy to solve. My main microphone for the TS-570 has been a Kenwood MC-60 for some time now, and it's switchable to either high or low impedance. I'm told that this works fine on the Drake gear, so I'll use it as-is and avail myself of it's dual-impedance feature which is controlled via slide switch on the microphone body (how often do you think I'm going to forget about that?).

CW has it's own set of problems. One thing I don't like about the built-in keyers on the TS-570 and IC-7000 is that you have to go menu diving to change the keyer speed. This isn't too bad on the 570 because there is a front-panel button that takes you there. It's a little more difficult on the IC-7000. But, what of the Drake gear? Obviously, the answer is to use an external keyer with a simple knob to adjust the speed. There are a number of nice PIC based keyers on the market, and they're relatively cheap. But, you can't key a grid-block rig with one. For that, it's easy enough to make a grid-block level adapter.

I picked K1EL's K40 keyer for this project because it has keyboard capabilities and a nifty LCD interface.


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Page last updated 29 Dec 2009