MarkAren wrote:
Hi All,

I keep noticing something which looks odd to me - I am sure it is
correct because this appears to be standard practice, but I would
appreciate it if someone could shed some light on the reasons...

Take a peek at http://web.telia.com/~u85920178/tx/500w-txt.htm (first
example I found). Specifically look at the 5 position switch on the
output matching, in position 5, the bulk of the inductor is shorted
out. This just looks plain wrong to me.

I assume that having shorted turns on an inductor like this drops the Q
drastically, or is this the whole point ?

Is the same true for roller coaster type variable inductors ?

Comments appreciated.

Thanks,

Mark.

I've pondered this question myself. I've only seen this done on
air-wound coils -- on a coil wound or a core this would be disaster. I
think the reason it's done is because if you _don't_ short the turns
you'd have all sorts of wierd resonance and/or high RF voltage effects
in the unshorted coils.

--
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com