[TowerTalk] Are_higher_HF_antenna's_really_better?

[Bill Ralston]

OK, I've got to throw in my $0.02, since I spent months playing with TA
trying to optimize antennas at my QTH.

1. There is more up to date propagation than the antenna book - I think it's
on the ARRL web site somewhere.  The newer data uses isotropic radiators at
each end of the path to allow all possible (not necessarily useful)
propagation modes.

2. In real life, arrival angles are not always symettrical at both ends of a
link - the ionosphere has tilts and non-uniform ionization that make all
sorts of weird stuff happen.

3.  Here's some _theoretical_ information for my QTH (DN30xl) on optimum
antenna heights (I have generally sloping ground up in all directions except
towards the NE). Results for DX heavily biased towards EU.  Average gain
computed over all elevation angles weighted by frequency of propagation at
that angle.

 80m: Higher=better for at least up to 130', terrain irrelevant
 40m: 80' for US, higher=better for DX up to 130', a stack helps (+2 dB on
average)
 20m: 50' for US, 110' for DX, 100/50 stack big win (+4 dB on average)
 15m: 30' for US, 90' for DX, 90/60 stack great (+5 dB on average), many
heights poor due to terrain
 10m: 70' for US and DX, 80/60 stack slightly better, many heights good due
to terrain

Note: for stacks, much of the gain is due to the ability to select either
antenna or both, depending on what combination has the best gain at a given
angle.

Obviously, my terrain has an impact - particularly when looking at the 15m
and 10m results.  I had originally planned on a single antenna at 70', and
as a result of this analysis (which in total is over 1Mb of Excel
spreadsheets and 6+ months of playing around) I decided the flexibility of a
tribander stack at 55' and 95' (with 40m at 110') was enough better than the
single 70' to be worth the extra work.  It is still a compromise.

My current small tribander at 45' works great, by the way, especially on
10m.

Location, local terrain, and conditions do mater. Anecdotal evidence is not
particularly useful.

-- Bill N7VM




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