[TowerTalk] An alternate yagi feed method
garyschafer at largeriver.net
Sun Dec 14 23:56:49 EST 2014
I had a TA33 up several years ago. With that strap grounding half of the
driven element it had a nice broad SWR on each band but it had two resonant
points! One was near where you would expect and the other was below the
band. They did recommend using the coaxial choke. Taking the ground strap
off gave a narrower and well defined SWR curve. I think that their intent
was to try and make the antenna broad banded (it met their SWR spec).
I called the factory and they acted as if they didn't know what I was
talking about. I left the ground strap off.
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
> Jim Thomson
> Sent: Sunday, December 14, 2014 9:12 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] An alternate yagi feed method
> After perusing through the Mosley.... tech notes, I see they use this
> alternate feed method on their
> various yagis. DE is split in the middle, and each DE ele half is
> insulated from the boom.
> They wire the center conductor of the coax to one side....and the braid
> to the other half.
> They then bond the DE ele half..that has the braid, to the boom ! Then
> no requirement for a balun,
> and no pesky CM current flow anywhere. Pattern is not affected. At 1st
> glance, it appears they
> have an unbalanced DE... fed with coax. Will this actually work ? A
> few weeks ago, I had previously
> drawn the exact identical config on paper...and wondered why it had
> never been written about in
> any book. I figured it must be fubar, but was still tempted to at least
> try it. Apparently Im 60 years too
> late, and am just re-inventing the wheel. Is Mosley out to lunch with
> their feed system ?
> To make the DE 50 ohms, Mosely resonates the DE at a lot lower freq than
> normal... to increase the feed point Z.
> This of course creates XL. The XL is tuned out with a series cap in
> each half of the DE, where the ele is split in the
> middle. Very similar concept to a .375 wave vertical, or inverted L on
> 160m. Mosley uses a short length of insulated
> wire inside each ele to provide the series C.
> Jim VE7RF
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