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From: khoward@chook.ua.oz (Ken Howard)
Newsgroups: sci.electronics
Subject: Re: How to switch high-voltage RF?
Message-ID: <3362@sirius.ucs.adelaide.edu.au>
Date: 23 May 91 03:41:22 GMT
References: <5170137@hplsla.HP.COM>
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From article <5170137@hplsla.HP.COM>, by tomb@hplsla.HP.COM (Tom Bruhns):
Writes: (concerning automatic antenna tuners)

>........
> that if it took over two seconds, something was likely wrong.  One
> of the failure modes was operation without an antenna connected.  It
> tried to tune its output terminal, and generally ended up creating a
> very high voltage node somewhere, one that would arc over.  It could
> usually tune a 5" piece of wire in the mid-HF range.  --  But maybe
> there's a lesson here about high RF voltages in tuners:  they can cause
> nasty breakdowns, so it's best to avoid trying to tune things that will
> be outside the range the tuner can handle.

Probably a good place for another timely warning here. I spent a while
designing an automatic antenna tuner for use with HF linear amps up to
2KW for an Australian communications comapany called Codan. During the
development work we made the painful discovery that if you tune for best
SWR there can be two possible modes: a) maximum power into the antenna
and b) maximum power dissipated in the tuner ... fun at 2KW!!!
Solution: course tune for max antenna CURRENT, fine tune for best SWR!


			---Ken---

Ken Howard, University of Adelaide         |      Phone:  +61 8 228 5198
	    Department of Computer Science |      Telex:  UNIVAD AA 89141
	    G.P.O. Box 498, Adelaide 5001. |      Fax:    +61 8 223 1206
	    AUSTRALIA.                     |      ACSnet: khoward@cs.ua.oz