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Re: Topband: alternative to vacuum variables

To: topband@contesting.com
Subject: Re: Topband: alternative to vacuum variables
From: "Joe Subich, W4TV" <lists@subich.com>
Date: Thu, 24 Jan 2013 21:28:21 -0500
List-post: <topband@contesting.com">mailto:topband@contesting.com>

> Making capacitors out of coax seems like an easy solution, however
> they end up being fairly lossy due to copper loss.  Think about
> it:  you would not deliberately make a capacitor long and skinny.

One way around this is to use multiple shorter sections in parallel.

One can also use series/parallel arrangements of fixed "doorknob"
capacitors to obtain the necessary voltage/current rating to pad a
lower capacity/wider spaced "breadslicer".

73,

   ... Joe, W4TV


On 1/24/2013 8:39 PM, Rick Karlquist wrote:
Pete Smith N4ZR wrote:
One of the reasons I have mot gone to high power on 160 is the cost of
capacitors for my omega match - at least $300.  Anyone know of any
workable alternative?  I remember someone writing about using coiled-up
RG-8, RG-213 or maybe Teflon coax.  Where can I find more information?

Making capacitors out of coax seems like an easy solution, however
they end up being fairly lossy due to copper loss.  Think about
it:  you would not deliberately make a capacitor long and skinny.
The only thing that makes them workable at all is that the heat
generated is spread out over a large area.  You would have to
carefully evaluate your proposed design to see if it were feasible.

Rick N6RK

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