Date: Tue, 31 May 2016 17:37:52 -0700
From: Grant Saviers <grants2@pacbell.net>
To: Jeff DePolo <jd0@broadsci.com>, towertalk@contesting.com
Subject: Re: [TowerTalk] Change in Frequency As Antenna Height Rises
A little sloppy, I should have said "transforms to some other SWR on an
SWR bridge".
We agree there are a couple of much better measurement means. Your
"lacking that" example still requires a measuring device that can do TDR
and complex impedance measurements which a classic "SWR Bridge" can't do.
It still seems a bit bizarre to me to be tuning individual elements of a
beam near the ground with an SWR bridge. Also, several classic
"great/proven" beam designs have been redesigned with good modeling for
much better performance out of the same pile of aluminum. And some well
known brands showed zero gain in the K7LXC et al yagi tests raising big
questions about "manufacturer's data.". It's gonna be hard to convince
me that there is a better way than good modeling to design a beam.
Grant KZ1W
## I have taken several brands of monoband yagis, like Telrex, wilson,
hygain, HB etc, and redone them all in software, usually YO-7.3 and
managed to enhance their performance by a bunch. In the case of telrex,
with its equal spaced eles, the best I could do is tweak the tips, even then,
the telrex performance was enhanced. So yes, software designed yagis work.
## I only know of a few folks who have checked individual ele resonance points
on any f12 N style 40m ele. And even then, they jive with the freqs that
F12 sez they
should resonate at.
## The f12 N version 40m yagis are 85% full size..and work exactly as
described.
They jive with the software, and the FB and gain curves vs freq match the
software.
## Now the old style F12 40m eles, the 39 ft ones and also the 44 ft ones,
that both used
LL wires, using alumoweld wire...coming back towards the boom were a pita to
tune. The shorting
wire on each side of the boom, had to be adjusted, to bring each ele to
resonate at a specific freq.
## The K7LXC tests were for trapped yagis. Mosley has no clue how to design
anything, and
still don’t, so its no surprise their heavy, long boomed, trapped yagis get
solidly trounced by a f12
2 el monoband yagi.
Jim VE7RF
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