[TowerTalk] VHF/UHF Common Mode Choke

Jim Brown jim at audiosystemsgroup.com
Fri Jun 28 18:32:24 EDT 2019

I recently did some work on chokes for 6M and posted the result to an 
email reflector devoted to grid chasers for that band. Two turns of 
RG8-size coax through a 1-in id. #31 clamp-on is optimum for 6M, and 
yields about 1K ohms resistive choking Z. I recommend at least two such 
chokes in series at the feedpoint. For RG8X or RG400, two turns through 
TWO 3/4-in i.d. cores is optimum for 6M, and yields about 1.2K choking 
Z. Again, use at least two such chokes in series.

For 2M, use multiple #31 clamp-ons, sized to fit the coax. Use the link 
below to select the size that fits your coax. Each will provide about 
250 ohms choking Z on 2M. Do not wind turns, just clamp them onto the 
coax. I would use at least five, and ten is better. :)   Arrow is a good 
vendor for parts they have in stock.


73, Jim K9YC

On 6/28/2019 11:50 AM, David Gilbert wrote:
> I've never been much interested in VHF/UHF, but with the current level 
> of solar flux and the summer static I'm thinking of giving it a try 
> using homebrew antennas based upon DK7ZB designs.  For 6m I'll 
> probably use a coaxial sleeve as a common mode choke (unless somebody 
> can suggest something better/simpler), but for 2m/70cm I'm planning to 
> build a dual band yagi with a common feedline and I'm not sure a 
> sleeve would work.

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