It is important to realize the disclaimer here ...mostly based on W5 prop.
I agree with the majority of what N5CQ has posted, especially the rules
for modeling.
Comments interspersed:
K4XS
In a message dated 4/16/2015 8:58:07 P.M. Coordinated Universal Time,
jlangdon1@austin.rr.com writes:
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.
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That may be true for W5 but I'll bet the boys in Maine would think that
was too high. I could have put my 4-stack for 15 at any height but to
accommodate condx for FL, 156 evenly spaced worked the best. It allowed me to
compensate for almost all arrival angles using BIP/BOP.
On anything more than a 4 high stack....not always so. I once had a 6
high stack starting around 165 feet for 10 meters. I was able to switch out
the top two, etc at any time. I can tell you it was a vacuum cleaner for
JAs and very useful for working that area when condx sucked. However, when
the band was really open the top 2 were no help.
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(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.
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I disagree. I've done BIP/BOP tests over 30 years with stacks from 40 to
10 meters at 4 different QTHs.. BOP will produce the best signals many
times for DX...more than the 15% here in FL on DX to EU as well as other DX.
For US, my 40 stack is almost 100% better to the east coast than BIP. The
only time BOP is never better is on real long haul stuff like UA0 or JT.
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...
(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.
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I disagree. Why put up a stack that is only good for one direction. You
get the benefit of a rotatable stack any where in the world...either using
a rotating tower or cheapo sidemounts. (I've done both and wouldn't do it
any other way.)
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(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
doesn't.
(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.
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Again, pay attention to the disclaimer...W5. For other parts of the lower
48 things can be quire different. Down in FL my 4/4 at 200/100 is a
monster west of the Mississippi and extremely useful in SS as is my 5/5/5/5
stack on 20 (west of the Mississippi). However, to accommodate high angle
stuff to W2. W8 etc on 40 I use a Yagi at 87 feet.
I am sure no one will want to comment! :)
73 and Good DX
John N5CQ
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