[TowerTalk] Antenna Height

[David Gilbert]

The terrain modeling program HFTA, written by N6BV and available free 
with 20th edition of the ARRL Antenna Book, will plot the takeoff lobe 
for various antennas over whatever terrain profile you specify.  It also 
has a neat feature that compares that takeoff lobe versus the optimum 
takeoff angles for various DX paths as calculated by IONCAP over a full 
11 year sunspot cycle.  The program is quick and easy to use, and since 
you live in Michigan, I assumed you had reasonably flat ground with a 3 
element yagi and did some runs for you.

HFTA says that a 3 element yagi 50 feet high over flat ground will have 
a broad takeoff lobe centered at 20 degrees elevation.  At 70 feet high 
the lobe is slightly narrower in the vertical plane with a peak at 14 
degrees.  Here are the predicted average relative (disclaimer .. read 
the previous three words a few times) signal strengths (70 feet versus 
50 feet) for the major DX headings from Michigan:

Europe    1.1 db
South Africa  2.0 db
South America  1.4 db
South Pacific   2.2 db
Japan  2.1 db
Asia  2.3 db

There are a lot of assumptions and possible errors behind these 
predictions, but as averages they should give you some idea of what you 
might expect.  The longer paths will, of course, benefit more from the 
additional height as shown above.

73,
Dave   AB7E



trife at sirus.com wrote:
> Secondarily, am I likely to see much improvement in performance for the extra 20 feet of antenna height, particularly on 20m?
>
>
> Thanks/73
>
> Tim
> KK9T
>
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