[TowerTalk] Change in Frequency As Antenna Height Rises

[Jim Thomson]

Date: Tue, 31 May 2016 17:37:52 -0700
From: Grant Saviers <grants2 at pacbell.net>
To: Jeff DePolo <jd0 at broadsci.com>, towertalk at 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