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Re: [TowerTalk] VHF/UHF Common Mode Choke

To: towertalk@contesting.com
Subject: Re: [TowerTalk] VHF/UHF Common Mode Choke
From: jimlux <jimlux@earthlink.net>
Date: Fri, 28 Jun 2019 17:49:01 -0700
List-post: <mailto:towertalk@contesting.com>
On 6/28/19 3:32 PM, Jim Brown wrote:
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.


Is 31 a good material for UHF? I always think of it as a HF material, but it could well be useful up to 500 MHz.

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