[TowerTalk] VHF/UHF Common Mode Choke

Dave Sublette k4to.dave at gmail.com
Fri Jun 28 18:58:23 EDT 2019

Using a T-match eliminates the need for a choke, for the most part.  I have
T-matches on everything from 2M to 70 CM.

Dave, K4TO

On Fri, Jun 28, 2019 at 6:33 PM Jim Brown <jim at audiosystemsgroup.com> 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.
> https://www.fair-rite.com/product-category/suppression-components/round-cable-snap-its/lower-broadband-frequencies-1-300-mhz-31-material-round-cable-snap-its/
> 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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