Bob Spooner wrote:
I have acquired a Johnson T-R switch snip

Hi,
Don't forget to include a low-pass filter
between the electronic TR switch
and the antenna. I got c.w. thumps in my stereo system
when I tried operating without a filter. I assume TVI would
be a problem without a filter, also.

The Johnson TR switch also works well when placed between
a separate receive antenna and the receiver. It actually
has a good noise figure, and provides some receive gain.
It works very nicely with a Collins 51S-1, due to its
50 Ohm output to the receiver. The 51S-1 requires a 50 Ohm
antenna for its front end tuned circuits to work as designed,
so a random length receive antenna can provide disappointing
operation otherwise.

Be careful about burning your hand - the Johnson TR switch
runs hot!

73,
Ed Knobloch