[TowerTalk] Fancy Coax Switches? Coax Crossbar?

[Jim Lux]

you might want to consider a fairly straightforward "relay module" that is a
simple PCB with the relays and a bit of drive electronics (kickback
supression diode, transistor with/without optocoupler drive).  You'd build
several of them and gang them up.  This has a lot of uses, and could be
remoted (for switching,e.g., tuning inductors or caps).  Then, program a
Rabbit or PIC or Basic Stamp to turn on and off the right relays at the
right time, given the PTT and band select info from the rig. A PAL or other
field programmed logic could also do the job quite nicely... even, perhaps a
diode matrix.

Some things to think about.. If you switch between antennas for Rx/Tx, you
might want to put a short delay (even just a relay would do) between
asserting PTT and returning "transmit enable" back to the rig (just like the
interaction between some rigs and linears), so that you can be sure that
you've actually switched by the time the RF hits the wire. (QSK might be a
challenge...)

If you DO go software control, think carefully about fail-safe, if the
software hangs up.  Configure the relays such that, for instance, there's no
combination of relay positions that can feed Tx power into the receiver
(which, by the way, is a failing of a simple NxM crossbar).  While relay
failures aren't too common, driver circuits short and stick high or low.

Jim, W6RMK
----- Original Message -----
From: "Brian Moran" <brianmo at yahoo.com>
To: <towertalk at contesting.com>
Sent: Friday, August 15, 2003 9:53 PM
Subject: [TowerTalk] Fancy Coax Switches? Coax Crossbar?


> I have a fairly modest setup of antennas (high G5RV,
> Tribander stuck in the trees, and low fullwave 80m
> loop), but have noticed a definite need to do some
> fancier antenna switching; for example, to transmit on
> the G5RV, but receive on the full wave loop, put one
> or the other antennas through a noise canceller, etc.
>
> Does anyone make a 4x4 coax crossbar switch that will
> also accomodate send vs. receive antennas?
>
> I'm thinking about building one (my 746Pro doesn't
> have rx antenna switching, which started this whole
> thing), but if one exists, I should probably check
> that out first!
>
> -Brian N9ADG
>
> Specs I've been kicking around:
> 1) Reasonably handle high power (JWS relay suggestion
> - thanks!)
> 2) Transmit/Receive configurations auto-switching
> 3) Have a configuration memory (0=20m tribander, 1=40m
> g5rv xmit, loop receive, 2=80m loop)
> 4) 4x4 or 6x4 config (two radio capability)
> 5) Tx inhibit line if relays are too slow
> 6) Cascadable (I aspire to a great antenna farm)
> 7) "repeats" the TX relay (using FETs) for external
> amps (may use up a contact that an amp needs, so
> provide an extra).
> 8) Optional: Tandem switching line for things like
> pre-amps, etc.
>
>
>
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