"JB" wrote in message
news:fuAtk.914$UX.763@trnddc03...

Electronic switches might not have the isolation you would prefer. With a
single band you have the luxury of hanging a stub on the RX port to short
the input during TX Otherwise, something should do that fast enough.
Since
there is 100w pep and I assume you measure 4v pp that is 16/51= .314 w pep
so:

10 log 100/.314 = 25 dB isolation. Not real swift. I would want better
than 35 dB Isolation. Even more for QSK. I wouldn't want to wait for the
RX to recover. I have equipment that burns out the input protection above
.25 w input (ave.)

You might not have trouble with a tube RF amp but...

The problem with a stub is that you still have to disconnect it somehow
during receive, right? I want to work full break in without listening to a
mechanical relay. From my tests, I've found that the T-R switch attenuation
isn't linear - higher power levels turn the switch off faster and produce
more isolation than low power levels, as would be expected with an active
device that used a sample of the output signal to drive a grid negative for
switching. My old Valiant II had an output of 275W for CW and isolation was
no problem for the HQ-170A receiver. I could hear my transmitted signal and
tell whether it was clean or not. Of course, the AGC on the 170A might be
better than the older generation NC-125 and NC-173 I'm planning to use. The
T-R switch is rated for up to 4KW, so it was just loafing even with 275W.
73, Bob AD3K