[Milsurplus] TR switches

[Bill Cromwell]

Pete Williams asked:


I'd appreciate info/directions to building a useful TR switch for HF and
capable of handling 500 or so watts. I have relays but not happy with
the
lack of fail safe facilities--- having experienced the RF coil on a
R-390A
smoking and not good for its health as result of relay hanging up in the
receive  position.

The ARRL  H/B 1985 edition has some examples  chapter 19-8 and am
attracted
to the version using the mosfet,  but wonder if there  are better/later
developments . 

Your experiences appreciated .

Pete VK3IZ

Hi Pete,

I built and used that exact electronic T/R switch in a homebrew amp. I'm
a QRP enthusiast so you will have to understand that a 90 watt amp to me
is QRO. That design uses a section of coax as the coupling cap into the
switch. I used RG-58. For your power levels you will need large diameter
coax. That T/R switch is intended to connect on the final amp side of
the output network so as to not transmit harmonics. That's exactly the
way I used it. I powered mine from a 9 volt battery and I never, ever
had any trouble with the rig. My cheap and nasty television located
about ten feet from the transmitter never suffered any TVI while I used
an end fed wire antenna.

Good luck with your project. Please let us (at least me) know how it
goes for you. By the way..I still have the T/R switch in it's shielded
compartment awaiting use in a new amp.

73,

Bill  KU8H