On Oct 17, 3:09*pm, Cecil Moore wrote:
On Oct 17, 9:52*am, K1TTT wrote:

that doesn't really 'solve' it, that just provides a single big
shorted turn instead of many turns.

Maybe the single big shorted turn IS the solution? :-) When there are
no actual shorted turns, i.e. all of the coil is exposed, does the
bottom section of aluminum tubing become that same single big shorted
turn?

no, it becomes a very small diameter and long shorted turn... but yes,
it is a shorted turn. you don't see as much effect because it is
smaller in diameter so the self inductance is smaller and it only
intercepts a fraction of the flux from the end of the coil. you get
more of an effect if you place an air core coil with its end near the
side or bottom of a metallic enclosure, the plate looks like a shorted
coil and can have large circulating currents.

In any case, one very conductive and very wide shorted turn is a
lot less lossy than a number of small shorted turns.
--
73, Cecil, w5dxp.com

that is why they get away with it, the losses in the big fat thing are
low enough that it causes less trouble than shorting turns with a
switch or relays.