[Moon-net] T/R relays

[Earl (Jim) Shaffer, WB9UWA]

HI Joe.

I have used these relays on 2M in a couple of different ways.
The first way is to decrease the inductance by shorting two adjacent
contact arms near the contact points. This reduces inductance substantially
and increases isolation. Remove the then unneeded wire. I simply
series resonate the remaining inductive reactance with a series capacitor
if need be. You then have two contacts that are normally contacting each 
other.
You also have a totally separate pair of contacts that connect when the 
relay is
keyed. To do a DPDT, you need to start with the typical 4PDT. It's probably
a good idea to use separate relays to improve any input/output isolation 
else
you may have an unwanted oscillator.


73, Jim Shaffer, WB9UWA.



----- Original Message ----- 
From: "Joe Taylor" <joe at Princeton.EDU>
To: "'moon-net-list-serv.davidv.net'" <Moon-net at list-serv.davidv.net>
Sent: Tuesday, December 18, 2007 9:28 AM
Subject: [Moon-net] T/R relays


> Does anyone on this reflector have experience using heavy-duty
> open-frame relays for QRO T/R switching at 144 MHz?
>
> Obviously this can be a workable approach at HF, and even at 50 MHz,
> where the resulting "impedance lump" in the signal path exists over just
> a small fraction of a wavelength.  I wouldn't want to try it at 70 cm;
> but what about 2m?
>
> I would be interested to hear if anyone has used such an approach
> effectively.  Is it a foolish idea, and just asking for trouble?
>
> -- Joe, K1JT
>
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