[TowerTalk] Ant switching

[Dick Green]

Tom,

I just finished my two-radio antenna switching system and would be happy to
share all the details with you. What you described is the best way to do it:
one two-way switch on each antenna feedline and one five-way switch on each
rig. However, using high-quality two-way switches, tees and right-angle
connectors, you can bus the two-way switch outputs for each rig together and
eliminate the two five-way switches. There's an excellent description of
this approach on the TopTen web site: www.qth.com/topten. However, you do
have to use high quality components and might experience a small increase in
SWR on ten meters with this setup.

Either way you do it, your setup can be manually switched or automatic.
Since I have only two feedlines running from the antenna farm to the shack,
my setup uses remote switches at the antenna farm end: six TopTen two-way
switches and two TopTen six-way switches. The two-way switches have a
lockout feature that prevents both rigs from accessing the same antenna at
the same time, which would effectively allow one rig to transmit directly
into the other (end of second radio.) I added an interface box with some
diode and IC logic to map 20M, 15M, and 10M to a tribander or multiband
vertical, tell me which rig is using which antenna and flash a warning light
when both rigs are trying to access the same antenna at the same time. I use
band detectors on the rigs to automatically select the correct antennas when
the frequency changes (my FT-990 supports an external TopTen band detector;
I had to make a "slight" modification to my TS950SDX and build a homebrew
interface to do that for the second rig.) Of course, you don't have to use
band detectors -- you can use manual switches to control remote relays.

Depending on antenna separation, you may need to install bandpass filters.
You can use 1/4 and 1/2 wave open/shorted stubs in the feedlines and/or
in-line filters between the rigs and amps (e.g., Dunestar 600.) There's some
great information on this at K1TTT's site, accessible through the W4RNL site
(http://funnelweb.utcc.utk.edu/~cebik/radio.html) My interface box has logic
and outputs for two sets of automatically switched bandpass stubs for each
band, which I'm in the process of building.

In addition to all that, I built a relay box to switch the key, mic, audio,
etc. between the two rigs. It's based on the schematic in the NA manual (NA
has excellent support for two-radio operation.) One enhancement I made is
the ability to automatically switch my 87A between the two rigs, taking
advantage of the amp's frequency detection and autotune features. The
switches were a tad expensive, but they saved me a bundle on a second amp. I
haven't heard of anybody else doing that, so maybe I actually invented
something new here!

Let me know if you'd like more details.

73, Dick, WC1M



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