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[TowerTalk] DC and UNUNs

To: <towertalk@contesting.com>
Subject: [TowerTalk] DC and UNUNs
From: W8IK@ibm.net (Joe Subich, W8IK/4)
Date: Wed, 24 Feb 1999 08:59:17 -0500

> 
> I had the situation at one time in the past. I used a couple of really
> large caps (.1uf @5KV, about the size of hockey pucks) that I found at a
> swapfest. I put everything in a plastic box, Caps on either side of the
> UNUN along with a high current rf choke to act as a DC path around the
> caps. Seemed to work fine. Thing to remember with this approach is that
> more than the voltage the caps need to be handle 8 to 10 Amps of 
> RF current.
> 
> Dave K9NX
> 

In practice, a single capacitor placed in the "ground" lead of the 
un-un should be all that is necessary.  The un-un will provide the dc 
path from input to output (the relay operating current is small enough 
that it should not present a core saturation problem with a reasonable 
size core) while the capacitor eliminates the dc short.  

The capacitor should be rated for at least 10 Amps (RF) which may be 
the real problem. 

73,
   ... Joe Subich, W8IK/4  ex-AD8I
       <W8IK@IBM.NET>
 

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