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To: topband@contesting.com
From: John Brosnahan <broz@csn.net>
Subject: Re: TopBand: New antenna on loaded tower
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> No one has ever written
>up a series of steps which, if followed, will ALWAYS result in a good
>match and an efficient antenna. If someone has written up such a
>step-by-step procedure for loading a tower, I've never seen it -- BUT I'D
>LOVE TO SEE IT! -- Fred K1VR
Shunt feeding of a tower suffers from the same problem that gamma
matching of a Yagi suffers. Depending on the driving point impedance
there are ratios of DE diameter and gamma rod diameter that can
result in "not being able to get there from here". Depending on tower
eight and number of Yagis it can be impossible to gamma match a
tower with a single wire shunt feed system. This problem can be
overcome by "fattening up" the gamma wire by making it a cage of
two or three wires with a similar width as the tower. Combine that
with an omega match (series and shunt variable C) and you should
always be able to match the tower, although there can be combinations
of matching values that result in reduced BW.
Gary Breed's (K9AY) article on shunt feeding of a tower in the
Low Band Monitor goes a long way to showing how one can ALWAYS
match a tower on Top Band.
73 John W0UN
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