Alan -
You're forgetting the loading coil has to be switched out
when
using the loop at HF, so the relay has to withstand the full
RF voltage
when using it as a vertical at LF/MF.
So you'll need a vacuum relay with a contacts rated at
something
like 10kV. The current will only be an amp or so. I tried
this once
using FR / Crydom reed relays that were certainly rated at
that sort of
voltage. Trouble was that rating was DC. At 137kHz it died
with a
flash from inside and melted contacts as soon as a decent
amount of RF
was applied.
A knife switch on a ceramic former would probably work,
otherwise find someone working for
NatGrid and try to get a 33 or 132kV contactor :-)
Andy G4JNT
