[TowerTalk] Stack-matching

[Lux, Jim]

On 7/19/22 5:24 PM, Joe Subich, W4TV wrote:
>
> Jim,
>
> The question wasn't about a transfer switch ... it was about
> a stacking switch that would allow the antennas to be fed to
> separate rigs when not used as a stack.
>
> 73,
>
>    ... Joe, W4TV


That wasn't entirely clear from the question..


Yeah, if you need Radio A connected to Antenna 1, or Antenna 2, or Both; 
and the same for Radio B.


I'd do it with 2 SPDT relays, because it's "foul up proof".  The common 
terminal goes to the antenna, the two switched ports go to the radios, 
with a T.

That way, no matter what state the relays are in (or if they get stuck), 
Radio A is never connected to Radio B.


If you do it with a pair of 1xN switch made up of SPST switches, then 
you have the risk of a stuck relay (or incorrect switching signals) 
connecting two radios.  You could probably do it with a pair of 1x3 
switches, and be "one stuck relay safe", but you still have the "wrong 
switching configuration" failure mode - with DC coils and some diodes, 
and some small signal relays, you could probably work out something that 
is failsafe.    Another scheme for safety (used in HV circuits) is 
grounding relays - you may wind up transmitting into a short, but at 
least the receiver doesn't blow up.


The whole "how do I connect N radios to M antennas" and keep good enough 
isolation, be fail safe, etc. is an interesting problem, especially when 
you're trying to use inexpensive surplus.