We all learn this sooner or later: Don't use ferrous metals to
conduct RF. If a metal fails the magnet test, it's out. Every time
I get some item of homebrew or something that's had a previous owner,
(transmitter or matching network) I go through with a magnet and see
if a previous owner or builder used steel around RF stages or matching
networks. Some steel alloys may be better than others but it's
impossible to tell, so out they go. Brass, copper, aluminum, silver,
nickel all okay. EF Johnson and perhaps others used steel nuts and
bolts that were plated with nickel. That's okay as RF current has the
skin effect.
What's wrong with ferrous metals? They don't conduct as well but more
important, at the microscopic level, they vibrate at the RF frequency.
This does two things: Generate heat, and slowly loosen clamp, as in
the case of a nut, bolt and washer for example.
Rob
K5UJ
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