>> switch? Is your reason for avoiding the relay that you don't want
> to have a failure in the middle of a contest, or is it the COST of
> the relay?
You can still have a PIN diode failure in the middle of a contest if the
antenna system begins breaking down.
For me the question is reduced to the operating environment at the station.
If there is occasion that SWR can exceed 2:1 at any time, high-power PIN
diodes will be less reliable than a vacuum relay, even with protective
circuitry. On the other hand, if you contest, and know that SWR will always
remain low and the line will not be subject to lightning-induced charges,
then PIN diodes are the ticket.
Amps like the Alpha 87A will do a reasonably good job at protecting the PIN
diodes from failure except during the times when you really need that amp to
perform (my experience anyway). And then there's the issue of the amp
going into bypass if its sees less than a well-performing antenna system -
at which point the amp is useless anyway.
Like the muffler, spark plug, and oil change scenario, vacuum relays can be
changed at regular intervals to reduce the likelihood of failure. In this
case, you can manipulate the odds in your favor - not necessarily so with
PIN diodes unless your antenna and transmission line is very well
maintained.
As long as a good, high-speed vacuum relay is used with an accelerator
circuit and is essentially noise-less, it's my pick 100% of the time.
-Paul, W9AC
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