On Sun, 13 Jun 2004 08:58:42 -0700, Jim Weir wrote:

But that's not the common failure mode. The common failure mode is for the
PTT/relay circuit to fail to respond to a "put me in transmit" mode. Thus, the
only isolation you have is from the splitter.

I've already said that you don't key the transmitter until all relay
positions are verified. You can do this at DC and still pass RF.

If you're really worried about this failure mode, put two
-independent relays in series.

Isn't that flawed logic like carrying a bomb with you on an airliner? The odds
of TWO people having a bomb are much smaller.

No. It's more like checking for a bomb twice. See above.

Lastly, I would not select a Wilkinson divider for the receiver. I'd
-use a transformer hybrid.

Your call. I note that under the common failure mode that your transformer
hybrid will have to handle the whole 10 watts. That's going to be one hell of a
transformer. The Wilkinson splitter will handle 50 watts without a whimper.

If the failure mode for the receiver is addressed, the failure mode
for the hybrid is addressed.

R-
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Robert Cherney e-mail: rcherney(at)comcast(dot)net