Geoff Haines, N1GY
Let me say right at the start, that I did not originate this idea. I have seen several articles in several different
amateur radio magazines on this idea over the years. When I found that I had a need for this device, it seemed obvious that
I would need to build it.
The concept is very simple. Take a commercially available switch box intended for switching data lines such as printer
cables between two computers, and change out the connectors so that it can be used to switch between two microphones to one
The best data switch box to use has a rotary switch knob and a multi-layer switch that controls 25 lines from one DB-25
connector out to two DB-25 connectors in. The switch works both ways, that is one line in to two lines out or two lines in
to one line out. Most of these devices do not use color coded wiring. The one I used had maybe 8 or 9 blue wires going from
the switch to each of the connectors, the other wires were all orange. This could be a problem if one was expecting to use
the color code to keep the wires organized.
There is an easy solution to this seeming problem. Just do not cut any wire off the DB-25 connectors until you are
ready to solder it to your microphone connector. Then cut the same wire in the same position on each of the three connectors
and solder each wire to the same position on each of the three mic connectors. Do each wire set one at a time old connector
to new connector and you will have no problem.
After you have filled all the contact positions in your microphone connectors, and any supplemental connectors such
as the external speaker/ headphone plug selection, simply cut away the rest of the wires to the old DB-25 connectors and remove
them. Now is the time to add the jack for the external PTT switch, if needed. It usually just gets wired across the contacts
for PTT that connect to the Boom Mic in parallel.
Now modify the chassis box to accept your microphone connectors as necessary and install the mic connectors in the
box along with any other jacks that may be required such as external speaker, earphone jack, or PTT switch.
After you test the selector switch to make sure that both mics work as they should, that the PTT switch on both mics
works, etc. then proceed to dress up the box as needed. A new label for the selector switch is all that is really required,
but you may also paint the box if desired.
Now that the selector switch is finished, it is time to plug in both microphones, the external speaker (if used) and
the PTT foot switch (if desired).
Plug the selector into the radio’s microphone jack and the external speaker
plug into the selector. Plug a patch cable if used into the radio’s external speaker jack and into the selector. That’s
it. You are all done. Now sit back and make some contacts with the radio.