Even with the isotropic sources, the data picks
the best takeoff angle, assuming antennas will
be adjusted to match at BOTH ends of the path.
It does NOT provide an answer to the question of
"What is the best angle for ME to use, assuming
the DX station has a LOW antenna?"
I assume your choices reflect WEST Coast propagation
to Europe which is a pretty long haul. Your comment
that terrain must also be accounted for is right on.
Your observation that takeoff angles are not always
symmetrical is also correct. When 10M is closing to
Europe, I notice the guys with higher antennas (60 ft)
are usually stronger than the guys with (presumably)
lower antennas, BUT, they are still stronger on my
LOW antenna, presumably because the sun is high
overhead at my location while it is dark in Europe.
>From east of the rockies, there are lots of times when
such high antennas take a back seat in the pileups.
N4ZC commented how he was getting creamed into
Europe by the 'shortie forty' crowd with 70 ft towers
in the late afternoon / early evening when using his
4L40 at 130 ft. He added a lower 2L40 and solved
the problem. Same for W3LPL at his previous QTH.
>From N4AR, we always opened up to Europe with
his 3L40 at 100 ft but used the 3L40 at 160 ft for
VK / ZL / LP where his high antenna dominated the band.
On 15M, I still have a vivid recollection of taking a
backseat in 15M pileups when using N4AR's 6L15
at 90 ft to chase multipliers in EU and AFR. When
I switched to a side mounted CC 4L15 at 50 ft I was
walking right through the pileups.
I guess all those anecdotal observations just don't
count. The computer analysis is always right. :-)
I've never seen a computer propagation program
that correctly shows the Low Band enhancements
at / after Sunrise. I guess they don't exist either.
In days of old, theories were thrown out if they
weren't supported by the evidence. Today, everyone
seems to ASSUME that the COMPUTER is right
and their observations must be in error if there is
IMHO, everybody would benefit from low antenna(s)
(35 to 40 ft) on each of the high bands to supplement
bigger and higher antennas. A small rotary tribander
on a separate tower or pole is a POWERFUL addition
providing both directional and waveangle diversity.
A pair of sidemounted simple dipoles (D3, etc) is another
alternative for single tower stations.
On Sat, 12 Jan 2002 11:23:00 -0700 "Bill Ralston" <firstname.lastname@example.org> writes:
> 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
> 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
> 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
> 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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