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
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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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