[TowerTalk] Antenna Heights, Stacking, and Siting
jlangdon1 at austin.rr.com
Thu Apr 16 13:38:46 EDT 2015
I have done lots of HFTA modeling and have years of experience and thousands
of hours listening to and switching combinations of stacked yagis on HF.
Here are my (primarily W5 area based) stacking rules of thumb, FWIW, YMMV:
(1) If the QTH is really flat, and by that I mean +/- less than 10 feet out
4 miles or more, the best stack set up for 15M is 30', 60', 90' and 120'.
More than a 4 stack will not be worth the trouble. Use the wavelength
equivalents for 40, 20, and 10. If your QTH is not that flat, do not pretend
that you can dispense with the modeling.
(2) 85% of the time on the air, using all four antennas in the stack will
produce the best signal. The other 15% is accounted for by (a) precipitation
static on receive is greatly reduced when you do not use the top antenna,
(b) lowest antenna is sometimes best for short domestic paths and high angle
multi hop summer F2 (but not necessarily for sporadic E), (c) long or
antipodal paths where the top pair will often be best, and (d) all other.
(3) Long path is usually not a big a contributor to contest scores.
(4) Multiple fixed stacks on EU and JA are a better long term investment
than a single stacks with rotators. A fixed antenna on SA/Caribbean will
produce lots of contest points per $, especially if you SO2R.
(5) You have to use a stack of at least two full size 3 element yagis on 40
to be able to reliably run both EU and JA from W5.
(6) Stacks of yagis are the least affected by poor ground conductivity,
verticals and inverted L's are the most affected.
If your QTH is not flat, throw out all rules of thumb and model the hell out
of everything before you break ground. Do not believe anybody's rules of
thumb will work for your non-flat QTH: they are usually anecdotal
observations specific to their QTH and not very useful for yours. You must
model to plan well. The unhappy surprises come from nearby hills and
valleys. The happy surprises come from gently sloping terrain.
Modeling rules of thumb:
(7) Try lots of modeling scenarios. Vary the heights by one or two feet and
watch for widely varying results. Believe a model setup that shows low
sensitivity to small changes in height. Be very suspicious of one that
(8) Moving a tower 100 feet horizontally can really change things,
especially if you have hills and/or valleys.
(9) When you have to change an antenna elevation on the tower a few feet
because of guy wire clearance, proximity of other antennas, etc. be sure to
go back and do the modeling with the new height before you build it.
(10) Do not assume that the highest points on your property are the best
spots for a tower. Play around with some other spots, too.
(11) If you only have one or two viable tower locations at your QTH due to
practical considerations like slopes, roads, property lines, etc. then model
the hell out of all your choices and permutations for those spots.
There is often a complete break between what you want for DX contacts and
domestic ones. At my current QTH, with some very fortuitous sloping
foregrounds, heights over 35' or so are highly counterproductive for
domestic paths to high rate QSO targets like California or along the east
coast. Optimizing for the SS, for example, would likely involve very long
boom yagis pretty close to the ground, where DX would dictate a 3 or 4 stack
of 'normal' yagis.
I am sure no one will want to comment! :)
73 and Good DX
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Roger
(K8RI) on TT
Sent: Thursday, April 16, 2015 9:11 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Antenna Heights
Remember, that when we talk of "best heights" that is a statistical number
and is not always the best height. I don't have the numbers in front of me,
but there was a good article in QST I believe last year.
Say, the best height is 60 feet 30% of the time, the other 70 % is spread
through a variety of heights. So, when going for the best height it just
means that height will be better than the others more often.
Higher might give stronger signals, but fewer times. "Best Height" is
dependent on frequencies, band conditions, and local soil conditions.
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