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Re: [TowerTalk] HFTA Accuracy / Usefulness

To: towertalk@contesting.com
Subject: Re: [TowerTalk] HFTA Accuracy / Usefulness
From: <donovanf@starpower.net>
Date: Thu, 19 Mar 2009 00:21:51 -0400 (EDT)
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Hi Pete,

I agree that arrival angle statistics generated with models using isotropic 
antennas produce an unrealistic bias towards very low angles (much less than 5 
degrees).

In the real world, only ocean-front full size vertical antennas and mountain 
top horizontal antennas actually produce very low angles.  The very few 
stations using such ideal locations (e.g., VP6DX) will soon be in your log 
anyway, even if your own antennas are far from ideal.

The most difficult QSOs are with low power DX stations in urban locations using 
low horizontal dipoles or short verticals over lossy terrain (e.g., the W3LPL 
QSOs with YI9HU on 40 and 20 meters in the ARRL CW DX Contest with his 6 foot 
rooftop vertical).

The ability to quickly switch among various antenna heights makes a big 
difference for these marginal QSOs.  In some cases very high antennas (150 to 
200 ft) are the best choice; however, antennas at moderate heights often 
outperform high antennas when propagation is good to excellent.

73
Frank
W3LPL






---- Original message ----
>Date: Wed, 18 Mar 2009 16:44:28 -0400
>From: Pete Smith <n4zr@contesting.com>  
>Subject: Re: [TowerTalk] HFTA Accuracy / Usefulness  
>To: Steve Hunt <steve@karinya.net>, 
>
>At 03:37 PM 3/18/2009, Steve Hunt wrote:
>>I developed an analysis techniques which correlates an antenna's
>>vertical response with the Angle-of-Arrival statistics published by
>>ARRL. Basically it gives you a "figure of merit"  for an antenna at a
>>particular height on a specific path and frequency. It's a useful tool
>>for analysing the trade-offs at various heights. It shows very clearly
>>that an antenna CAN be too high.
>>
>>QST will be publishing it next month or the one after. If you want a
>>"sneak preview" the same material in a different form is presented on my
>>web-site:
>>http://www.karinya.net/g3txq/hexbeam/height_2/
>>
>>73,
>>Steve G3TXQ
>
>
>Steve, I published substantially the same method in the US National Contest 
>Journal in January 2001, with a correction in the September/October issue 
>to incorporate the point about applying the weighting to linear rather than 
>logarithmic relationships.  N6BV incorporated a Figure of Merit using the 
>same method in the first version of HFTA, which has been out since around 
>2003 or 2004.
>
>A rather more interesting question to me, at this point, is what antennas 
>should be specified for the two ends of the path to generate the arrival 
>angle statistics.  There is a discussion of this on the ARRL TIS web page, 
>but as far as I'm concerned the jury is still out on that subject; in the 
>past, I had argued for isotropic antennas on each end of the path, so that 
>the statistics would reflect the actual behavior of the ionosphere rather 
>than the selection of antennas.  I'm now coming around to a somewhat 
>different view, if what you're interested in is trying to open up the most 
>"layers" of stations to work in a contest, for example.  At some point, the 
>lowest layers are guys with low dipoles or lossy ground-planes.
>
>With luck maybe we can smoke Dean out and restart the discussion.
>
>73, Pete N4ZR
>
>   
>
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