[TowerTalk] Another way to make a CM choke ?

Jim Thomson jim.thom at telus.net
Fri Dec 15 15:37:50 EST 2017

Date: Thu, 14 Dec 2017 20:26:16 -0800
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Another way to make a CM choke ?

<And not a very good one, because it fails to consider the common mode 
<circuit of which it is a part.

<73, Jim K9YC

<On 12/14/2017 1:48 PM, David Robbins wrote:
> Ancient reference for aircore baluns:http://www.k1ttt.net/technote/airbalun.html

##  The chart goes from 1 mhz  up to 30 mhz,  in 1 mhz increments.  As noted he did
NOT depict the exact freq of resonance.   But the concept works, with extreme high Zs
and all resistive, when at exact resonance.  Albeit, they are narrow banded devices, as can
be seen when going just plus or minus 1 mhz !   To tweak these correctly, they would have to 
be shifted in freq, by adding or subtracting turns, which of course adds or subtracts both uh
and C.    It would take some mucking about, but ideally, one could get the resonance point
either inside a ham band, or just above a ham band.  If just above a ham band, then a small
amount of external C between  input  and output braids  would lower the resonance... low
enough to fine tune it to the band of interest. 

##  But for 160-80-40m, it will use one helluva lot of coax, to even get close to working with a 
high Z,  so its impractical for the lower bands, and marginal for the upper bands.   Final verification
could easily be done with any clamp on RF ammeter. 

Jim   VE7RF   

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