[TowerTalk] An alternate yagi feed method
robrk at nidhog.net
Sun Dec 14 22:27:49 EST 2014
On 12/14/2014 10:11 PM, Jim Thomson wrote:
> 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
My 1960 TA33, in 1980, had a broken DE insulator. Made one from a chunk
of 2" plexiglas.
Never could accept their feed, so tossed the ground strap and made a
coax "Collins" balun.
Worked fine for 20 more years.
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