Richard Clark wrote in message . ..
....

Seems unlikely. PIN diodes (or any diode for that matter) would have
a very difficult time switching 300W voltage potentials far in excess
of the diode's own intrinsic boundary potential. PIN diode switching
is most often employed in receive circuits where the signal level is
considerably smaller than the switching potential. Then, on the other
hand, they may have huge power sources capable of blocking the RF
potential swing anticipated at the node the PIN diode serves (talk
about cost!).

Dunno about using PIN diodes to switch turns in a helix for an
antenna, but for sure they are used as TR switch elements to some
rather high powers. The usual switch topology turns on two diodes
during transmit so that there is little RF voltage across either, but
certainly they can work fine with P-P RF voltage up to their reverse
breakdown voltage, which can be hundreds of volts. (Some 1N4007s are
actually PIN structure, for example.) They can be put in series to
stand off more voltage if necessary. Just takes a very low current DC
bias voltage at half the breakdown.

I believe the HF radio used in P3 aircraft after they decided that the
ARC-94 didn't have enough frequency stability and resolution had an
electronically-switched tuner which I suppose used PIN diodes.
Perhaps some lurker knows for sure. That was quite a long time ago.
There are probably bunches of examples of power switching which also
require voltage standoff since then.

Cheers,
Tom