Re: [TowerTalk] VHF/UHF Common Mode Choke

The DK7ZB designs I plan to use give a 50 ohm impedance at the center of a single split driven element.  A small amount of gain is sacrificed to accomplish that.  I modeled the designs in EZNEC+ and they appear to be spot on.  In addition, quite a few VHF/UHF enthusiasts in Europe have built antennas per his designs and verified the 50 ohm feedpoint impedance. So all I really need is a common mode choke, and I will probably use the clamp-on ferrites that K9YC suggests. Thanks es 73, Dave   AB7E On 6/28/2019 7:33 PM, Glenn Pritchard wrote:

A folded driven element is inherently 200/300 ohms, if you take the Sinclair or Comprod antennas there is a 96 ohm transference within the element when they talk about open dipole (feed point open) or closed dipole as in the phasing. I made a 7 element yagi with a folded dipole driven element from a 210-C1, designed the antenna around the driven element. With a yagi, without this arrangement you have to take the inherent 300 ohms down to 53 ohms, hence the balun. I did a LOT of work with similar antennas when I was with CNCP Telecommunications and Unitel here in Canada. Glenn, VA7UO On Fri, Jun 28, 2019 at 5:47 PM jimlux <[email protected]> wrote:

On 6/28/19 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. I guess it might, since 1/4 wave and 3/4 wave (432/144 = 3.00) accomplish pretty much the same thing, but I'd like some input from VHF/UHF hams who would know better than I. And if a sleeve balun is indeed the way to go, what is the best way to fabricate one at UHF?  As W8JI points out, coax jackets aren't necessarily a low loss dielectric at UHF. Thanks much for any suggestions.

• [TowerTalk] VHF/UHF Common Mode Choke, David Gilbert
  • Re: [TowerTalk] VHF/UHF Common Mode Choke, Jim Brown
    • Re: [TowerTalk] VHF/UHF Common Mode Choke, Dave Sublette
      • Re: [TowerTalk] VHF/UHF Common Mode Choke, David Gilbert
    • Re: [TowerTalk] VHF/UHF Common Mode Choke, jimlux
      • Re: [TowerTalk] VHF/UHF Common Mode Choke, Jim Brown
  • Re: [TowerTalk] VHF/UHF Common Mode Choke, jimlux
    • Re: [TowerTalk] VHF/UHF Common Mode Choke, Glenn Pritchard
      • Re: [TowerTalk] VHF/UHF Common Mode Choke, David Gilbert
      • Re: [TowerTalk] VHF/UHF Common Mode Choke, Wes <=
      • Re: [TowerTalk] VHF/UHF Common Mode Choke, Máximo EA1DDO_HK1H