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[TowerTalk] Vertical vs Yagi

To: TowerTalk <towertalk@contesting.com>
Subject: [TowerTalk] Vertical vs Yagi
From: David Gilbert <xdavid@cis-broadband.com>
Date: Mon, 06 Apr 2009 09:42:06 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
This whole thread illustrates the dangers of making generalizations.  
There are so many factors that affect antenna performance, even well 
constructed ones, that in my opinion it's not very objective to make 
absolute statements.

1.  Optimum takeoff and arrival angles vary according to solar 
conditions, band, and whether the path is open or opening/closing.
2.  Antenna vertical response patterns vary according to height and 
ground conductivity, both of which are huge variables in practice
3.  Perceived antenna performance is affected by relative noise, and 
that's a function of both vertical and horizontal response patterns
4.  Polarization affects not only ground losses, it also affects 
propagation characteristics, especially for the low bands

I think point #4 has some bearing on the discussion regarding a vertical 
versus a high dipole on 160m even when EZNEC predicts similar results, 
and I'm really surprised that nobody so far has referenced the 
gyro-frequency effect espoused by propagation expert NM7M and others.  I 
don't pretend to understand the physics, but the concept says that the 
rotational frequency of electrons around the magnetic lines of force in 
the ionosphere (being about 1 MHz) strongly affects the absorption of 
signals as they enter depending upon polarization ... or something like 
that.  Vertical polarization is attenuated much less than horizontal 
polarization depending upon QTH and direction of the path.  At one point 
a few years ago I had a 160m dipole hanging about 280 feet in the air 
across a canyon behind my house.  I was kind of proud of the European DX 
I was working with it from Arizona until NM7M sent me an email telling 
me that for my QTH he had calculated an eleven db (!) handicap for 
horizontal polarization.  80m is apparently affected as well, but 
considerably less so, and 40m and above are not.


73,
Dave   AB7E


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