Topband: Fabricated common mode chokes - Sourcing

Jim Brown jim at
Wed Aug 31 07:34:35 PDT 2011

On 8/30/2011 10:30 AM, ZR wrote:
> Did you open up a Cushcraft balun to discover that method? I believe some
> other companies do similar and Teflon wire is used so it doesnt char as does

"These methods" are well documented in the literature, especially Jerry 
Sevick's work (W2FMI). In one of his later books, he discussed some 
chokes wound with THHN, noting that their Zo was on the order of 100 
ohms.  What I have NOT found in the literature are discussions of the 
significance of choking impedance, nor of measurements of choking 
impedance.  I may have been the first to do that for common mode chokes 
outside of the military.  A few years ago, after I published my work, 
someone sent me a military research document that did so in the 70s (and 
reached the same conclusions that I did).

As to charring -- that's an issue if the device in question is seeing a 
lot of dissipation.  Properly designed and applied, chokes should NOT 
see a lot of dissipation unless they are being used in series/parallel 
combinations to do impedance transformation.

73, Jim Brown K9YC

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