Stefan,
The feeder is 10mm diameter stainless steel. I guess it takes at least
300A before it melts :-) So the limit would be the withstand voltage of
the ceramic isolator, even on MF :-)
Brings back an old memory - from about 40 years ago. My boss and I were
doing some routine maintenance on the power divider for a 3-tower AM 5kw
broadcast array on 580 kHz. The box (circa 1939) had a fairly large coil
for power division, and a couple of networks for matching and a part of
the phasing. The big coil therefore had a bunch of taps, including one
to short out some turns at the "hot" end. The short was done with an old
piece of tinned braid, and its position had to be shifted a couple of
times a year.
My boss remarked that the jumper (about 15 cm) was looking sort of
ratty, so I suggested that we replace it with a solid copper strap. He
remarked that he had always wanted to try a nice shiny piece of 1.2 cm
stainless-steel "Wraplock" as an RF conductor. We had several rolls of
it, used in securing conduits and cables to towers. So he cut off a
length, drilled the needed holes, and we put it in place. Turned the rig
on, and the current into the divider was normal. Then it started to
drop. And drop.
Killing the transmitter, we opened the cabinet, and found a nice black
stainless steel jumper that was still very warm. We switched to copper,
and all was fine. I'd guess that the current through the strap was
around 10 Amps -- not sure after all these years. So, I'd suggest
treating stainless-steel with caution as an RF power conductor!
John, W1TAG
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