Keep in mind that the old telrex monobanders used a half wave phasing line
to feed the two sides of a t match, this is not tuned like a gamma or driven
like a split element with a balun... the impedance is, I think, 100 ohms on
each side so when paralleled at the feed coax it matches to 50 ohms. It is
'properly' unbalanced and designed to be fed with coax so a choke or other
balun should not be necessary.
HOWEVER! These designs were not the best in the world, especially when
compared to todays designs. If these are the longer ones like the 6 or 8
element designs I highly recommend running them through an optimizer. When
I did that years ago with YO it optimized away an element or 3 turning both
the 6 and 8 element ones into long boom 5 elements. You have to keep the
other elements for wind and weight balance, but they get shortened enough to
make the electrically neutral. The shorter 3 and 4 element ones could not
be optimized as well, but may still benefit from a bit or updating. The big
10m one was also way out of band, when analyzed with today's software it
made a great 11m beam, but was bad on 10m.
David Robbins K1TTT
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:towertalk-
> email@example.com] On Behalf Of Bee Walton
> Sent: Friday, July 18, 2008 22:25
> To: firstname.lastname@example.org
> Subject: [TowerTalk] Yagi Balun
> Three 29 year old TELREX MONOBAND yagi's are off the towers and on the
> ground for maintenance and repairs. The factory made and installed coax
> baluns will be replaced. If the baluns are replaced with a ferrite-bead
> type 1:1 balun such as the Force-12 brand, will the antenna pattern or
> other factors be changed?
> Bee K4JLD
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