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Topband: Radio Arcala, HFTA, elevation angles

To: "topband@contesting.com" <topband@contesting.com>
Subject: Topband: Radio Arcala, HFTA, elevation angles
From: "k9la@frontier.com" <k9la@frontier.com>
Reply-to: "k9la@frontier.com" <k9la@frontier.com>
Date: Thu, 25 Oct 2012 05:32:46 -0700 (PDT)
List-post: <topband@contesting.com">mailto:topband@contesting.com>
More comments.
Radio Arcala – My only experience with them is in CQ WW CW a couple years ago. 
There was another OH up that a way running a vertically polarized antenna (I 
don't remember at the moment if it was a vertical or a 4-Square). This other OH 
had a stronger signal than Radio Arcala for the several times I checked. Note 
that this is not an extensive comparison. As a side comment, when Radio Arcala 
announced this project, I expressed my concern to them – but by then it was too 
late. Regardless of the results, we're going to learn something (as GM3POI 
pointed out).
HFTA – Those 1.8 MHz elevation angles likely came from IONCAP/VOACAP as the 
program does give results below 2 MHz. The real issue is there is very little 
(if any) validation data on 160m.
Elevation angles on 160m – I believe useful elevation angles on 160m fall into 
three categories. With the nighttime E region critical frequency around 0.35 to 
0.5 MHz, elevation angles below about 10 degrees are refracted by the E region 
(in other words, E hops). The importance of these extremely low angle E hops is 
not well understood. Higher angles can result in ducting at night as long as 
the electron density valley above the E region peak is well formed. My guess 
for these angles (from ray tracing work with Proplab Pro) is something like 10 
to 20 degrees. Above 20 degrees, the wave passes through the E region and is 
not refracted enough to get into the duct – so we get F hops. Please realize 
this is a very general summary, as “stuff” happens.
160m differences – When considering propagation on any band, one has to 
consider refraction, absorption, and polarization. With refraction by a given 
electron density profile inversely proportional to the square of the frequency, 
160m is bent the most and results in shorter hops. Due to 160m being close to 
the electron gyro-frequency (one of N0AX's favorite words), absorption is more 
than on our HF bands. This results in shorter hops with more loss. In fact, the 
extraordinary wave (one of two characteristic waves that propagate thru the 
ionosphere) is usually considered out of the picture on 160m due to 
significantly more absorption than the ordinary wave. And again due to 160m 
being close to the electron gyro-frequency, polarization tends towards highly 
elliptical as compared to circular polarization on our HF bands. And vertical 
polarization couples the most energy into the ordinary wave at the high 
latitudes.
Carl K9LA
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