Radio W4KAZ

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W4KAZ SO2R Collection – Engineer The Possible -SO2R part 2

At the bottom of this page is an accumulation of some of the SO2R resource materials I used in developing my own custom SO2R solution. My first SO2R post hashes out the thought process involved in choosing the homebrew methodology for hacking together a workable SO2R set up via home brew components.

The big issues for customizing an SO2R capability appear to me to be philosophical. It is possible to wear two sets of headphones and manually switch everything, praying you don’t transmit from radio A into radio B. That is a bit TOO minimal, even for me. A minimum SO2R set up for my purpose came down to an audio switch box, a switch for the CW, microphone, and PTT, as well as band pass filters and filter switching(manual and/or automatic).  And something like the Array Solutions SixPak to “keep ’em separated”[cue “The Offspring”].

It turns out none of those components are out of reach for home-brewing – if you are willing to compromise. The audio and radio input functions can coexist, but they could also easily be separated into two discrete units. One unit to handle headphone audio and the second for CW/MIC/PTT switching and route band data(if used). Likewise, the filters, switching, and band decoder for automatic antenna/filter switching can all be discrete units.

The crucial decision is whether to use USB(New Hotness) versus serial/parallel(old-n-Busted) interfacing. It didn’t take very long to determine that Old-N-Busted was going to be much easier to twist up in the KazShack. YMMV, and it is a VERY subjective decision. For my own uses it is just simpler to use the parallel interface, even if it requires milking the life from a few old computers running un-supported OS’s. But I suffer no illusions that “simpler” equates to “better”. That’s a subjective call, and will depend upon the circumstances and resources available.

Building a custom SO2R set-up grew out of my interest in a project by Jim, K4QPL, as well as my interest in filters, both band pass filters and coaxial stub notch filters. Being able to scout a second band will be fun, and it isn’t a great leap from a bit of extra S&P to full two radio operation. I don’t expect to be very proficient at it, but running at low power into mediocre antennas is not terribly productive either. So a full integration of the second radio into the station set-up might be fun.

All of those considerations lead to researching the topic. Others have done a good job of documenting certain things via the internet, so I’m just aggregating a few of the links I found useful. Some are ideas I have incorporated, like the band pass filters. The filters merit their own separate treatment. Some of the other SO2R links discuss ideas that seem to have merit, but did not apply to my situation. Some are just good reading.

The first set of links are station specific information, posted by folks describing their own SO2R set-ups. My own customized designs will be referenced first, simply because I can. But just so it is clear, my own design is an amalgamation of the work of others, including K4QPL, KK1L, and others.

Many thanks to K4QPL. Jim sparked my initial interest in this project via a club program about his own SO2R project, and answered several philosophical questions that led me to my own research and experiments.

The next set of links point to reference materials or other sites aggregating similar links, or some of the commercial sources. Note: There is a lot of duplication and cross linking. K8ND’s site has a good round up of the commercial sources from here in North America.

Hardcopy Reference:

2004 ARRL Handbook, Chapter 22.47, “A Computer Controlled Radio Switch Box”

Last Amended 9/20/2009, w4kaz

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