[TowerTalk] TH6DXX at various heights

Mon Sep 8 07:19:14 EDT 2008

Steve,
Thanks for the info!
This should be an interesting adventure!

Thanks & 73,
Gordon Beattie, W2TTT
201.314.6964

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Steve Hunt
Sent: Monday, September 08, 2008 8:38 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] TH6DXX at various heights

Gordon,

There's a couple of pages of information about antenna height on my web 
site that you might find interesting, particularly the second page. They 
are part of the Hexbeam section, but the data applies equally to any 
beam. The conclusions were:

"For those of us constrained to use a single multiband antenna mounted 
at a fixed and modest height, the results offer some encouragement: if 
we can get the antenna up around the 40ft-50ft mark we will be within 
1dB of the optimum height for short-haul and medium-haul paths on all 
bands 20m thru 10m. And we will probably accept the "half S point" 
penalty that our modest height suffers on the long-haul paths.

If our antenna is presently at the 20ft mark, the effort and expense 
required to lift it to around 40ft looks well worthwhile; we will see 
improvements ranging from 1dB to 5dB, depending on the path and the band.

For the "serious" operator who is able to justify the expense and 
engineering challenges of lifting the antenna to 80ft or more, the 
results show that significant benefits will accrue on the long-haul 
paths; but the ability to switch to a lower antenna under certain 
propagation conditions becomes increasingly important, particularly at 
the highest frequencies.

Finally, a note of caution! The HFOM involves a weighting factor based 
on arrival-angle statistics. This means that, even though we may have a 
good /average/ HFOM, there may still be times when the antenna performs 
poorly. For example, the Hexbeam at 80ft produces a reasonable HFOM of 
8dBi on 20m short-haul paths. However, if at some particular instant the 
signals are arriving in the range 22° to 26° (which they will do over 
25% of the time), we will wish we had another antenna at a different 
height we could switch to!"

For more details, including an explanation of what I mean by HFOM, see:

http://www.karinya.net/g3txq/hexbeam/height/
http://www.karinya.net/g3txq/hexbeam/height_2/

73,
Steve G3TXQ

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