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Re: [TowerTalk] step away from steppir, Son

To: <>
Subject: Re: [TowerTalk] step away from steppir, Son
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Thu, 14 Jun 2007 07:15:47 -0400
List-post: <>
While we all agree all antennas have losses and bandwidth 
limits, there isn't much useful in all this subjective 
hyperbole about traps having "astonishing losses" and 
"optimization on 14.015MHz will make the pattern junk at 

When it comes  antennas we're all victims of marketing and 
rumors laced with very little fact. Some of the claims from 
the most vocal are laughable, like six dB gain when going 
from 50 to 300 radials and special Quagis with 20 dB over 
monobander performance. And yes, these are real numbers 
offered by real people! Just as bad are the "way better than 
a 4 element monobander", "patterns are junk" and 
"astonishing loss" claims.

One antenna manufacturer who loves linear loading claimed 
traps have 1dB loss per trap, another number obviously 
pulled from deep in that hole in our backsides.

I have a line isolator from a company that claims or claimed 
50k ohms isolation across HF, and it fact it never reaches 
anywhere near that value on any frequency and is only a few 
hundred ohms on some bands! Something like this is beyond a 
simple mistake, it requires almost zero understanding of 
what we are talking about!

A person very well known and well respected for antenna 
modeling (and one of the best engineers I ever met) and I 
had a good conversation at Dayton about Ham antennas and 
gain. He was hired on two different occasions to model 
amateur antennas, and in both cases the widely accepted 
claims of two different manufacturers were obvious junk 
science.  (No, he didn't mention who or what they were.)

My 40 meter Yagi at 140 feet, and it is tougher to get a 40M 
antenna to be broad than a ten meter antenna, has about 6.2 
dBd measured gain at 7000kHz. It has 6.6dB at 7250kHz. This 
is compared to a real dipole at the same spot by measuring 
500 feet away on a 300 ft tower in the main lobe of the 
antenna. It is set for optimum F/B at 7100kHz, but it has at 
least a 40dB null in the middle of the rear null on either 
7000 or 7200kHz.

What really falls apart in pattern? The ANGLE of the rear 
null moves around. I can get a boom truck and fiddle with 
the elements until I almost can't measure the rearward 
signal at a certain angle, but if an element flexes just an 
inch the null moves and the null is 30dB less deep at the 
same angle. The overall average F/B and gain doesn't change 
much at all, but if I was all focused about one certain 
angle on one frequency I could make it sound like a 
bandwidth disaster.

If a thread is going to take up 250kB of hard drive space we 
should at least try to stay somewhat around the real world 
expectations. This stuff is starting to sound like CB 
antenna specmanship or a discussions about religion.

73 Tom


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