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Re: [TowerTalk] Capacitors To Tune 160 Vertical

To: Bill Turner <>
Subject: Re: [TowerTalk] Capacitors To Tune 160 Vertical
From: David Gilbert <>
Date: Wed, 05 Dec 2007 14:02:31 -0700
List-post: <>

I don't think you get it yet.  Normally I'd let it go but you're going 
to mislead a lot of people here if I do.

The original question involved capacitors in the range of 1000 pf, which 
at 1.8 MHz have an impedance less than 100 ohms.  That 100 ohms is in 
parallel with whatever leakage the dielectric might have.  It would take 
a pretty defective capacitor for the RF voltage across it in any series 
configuration to divide in any way other than per that 100 ohms AC 

Besides, if the leakage was that bad and it was part of a parallel 
combination, Q would be horrible and the capacitor would burn up because 
of the excess current.  Just the opposite of what you stated.

I'm not in any way suggesting that anyone "just slap together some 
capacitors without further thought".  Quite the contrary ... I'm 
suggesting they simply take into account basic electrical theory when 
deciding on a configuration.  You should do the same.

Dave   AB7E

Bill Turner wrote:
> On Thu, 29 Nov 2007 12:15:26 -0700, David Gilbert
> <> wrote:
>> I don't understand that comment.  Murphy's Law has nothing to do with it 
>> ... Ohms Law does.
> ------------ REPLY FOLLOWS ------------
> Murphy will be glad to provide you with the occasional capacitor which
> has considerably more leakage than another. In a parallel circuit,
> this may be of no importance, but in a series circuit it may be fatal.
> Likewise, since this box is going to be outdoors, Murphy may cause dew
> to condense more on one cap than the other, again of little or no
> consequence in a parallel arrangement.
> These things can be overcome, but the designer must take them into
> account before construction begins. Just slapping a couple of caps in
> series with no further thought is asking for trouble. 
> 73, Bill W6WRT
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