Hi Tom, et. al.,
I'm right now debating whether to put my quad back up at 120 feet.
It is now at 90 feet. It is used primarily on 20 meters, but once
in a while on the other four bands up to 10 meters. My comments
are concering 20 meters.
First, I want to hear more from you big guns that have multiple antennas
at different heights. I wish I could talk to Simon, OH8OS, who
did a study on this years ago with his 36 element array. I would love to
have some statistical data with notes on how much difference there is
between the same antennas at different heights on different paths. If
someone would provide me with that I would be glad to do the mathematical
analysis to make sense of it. It would make a very interesting paper
that I'm sure all of us would wish to read.
Second, I'd like to add my experiences to those of others. My data has
not been collected scientifically, but comes from many hours operating
on the 20 meter band and gathering every thread of information on what
makes a big signal there.
QTH matters. The best QTH I know of is the middle of a large salt
marsh. Gale Alred, (KL7G, KL7JW & before that KL7BJW) had one kind of
like that. The antenna should be about 120 feet above that kind of
reflector, and should be a monobander. I'd like to know of other
big guns' QTH situations.
My present methods of analysis tend to give preference to the long
paths, because there are no really active locals that I can compare
with. I have been comparing with others in the Pacific Northwest
and note that on the long path, the antenna at 120 feet worked
about an S unit better than it does at 90 feet. For the short path to
Europe, it is about the same sometimes, and other times it seems to
be worse, especially when the band is just opening or closing.
Anyone know of any scientific studies along these lines or of these
questions?
73,
Rob, KL7NA/W7
>
>
> On Wed, 27 May 1998 22:22:22 -0500 Tom Champlin <w0hh@ix.netcom.com>
> writes:
>
>
> >.....snip.... I have a 40-2cd in the basement I never
> >finished, because, frankly the thing needs to be up at about 140' to
> >have any real gain.
> >
> >Tom W0HH
> >
>
> WRONG !
>
> This kind of thinking results from the misconception that DX signals
> ONLY propagate at the lowest angle that will link two distant locations
> in
> the minimum number of hops. Most propagation programs list the
> waveangle that corresponds to this minimum number of hops.
>
> In actuallity, the ionosphere will support much higher waveangles.
> Several factors can combine to produce the strongest signal at
> waveangles higher than those corresponding to the minimum number
> of hops. These include absorption in the D layer (which is higher
> for low angles since they spend more time in the D layer), LOW
> ANTENNAS at the DX end (which radiate more energy at HIGHER
> angles), and DUCTING effects and E-layer effects which take high
> angles and bend (refract) them to lower angles aimed at the F layer.
>
> It is fairly easy to determine the highest angle that will propagate:
> Simply observe the closest stations that are heard via ionospheric
> refraction. Knowing this SKIP distance, and the height of the ionosphere
> will yield the highest angle supported by the ionosphere (see graph of
> waveangles vs. distance published in ARRL Antenna Books and other
> sources).
>
> >From 40 years of DX and contest experience, and discussing antenna
> performance vs. height with station owners having more than one 40M
> beam, my opinion is that 80 to 100 ft is optimum on 40M during the
> late afternoon and evenings. Higher antennnas (140 to 200 ft) pay of in
> the
> early morning, especially just before sunrise and just after sunrise on
> the
> LONG PATH to Central Asia and the SKEW PATH to SE Asia (from eastern
> USA). Everyone I know with both high and low 40M beams uses their
> LOW antenna for the evening opening to Europe and Africa.
>
> Even if you can't get a 40M beam up at 80 ft, it is still beneficial.
> Did you
> ever hear A22MN on 40M? His big signal originated from a 40-2CD at
> 50 ft.
>
> By now, most readers are tired of hearing me tell about how my 40 ft high
> TH7 is often my BEST antenna during daylight hours on the high bands.
> You need BOTH high and low antennas to cover ALL of the waveangles
> supported by the ionosphere and the LOW antennas will OFTEN outperform
> higher antennas when MUF's are higher than the band in use.
>
> de Tom N4KG (with 20 antennas on 7 towers from 40 to 140 ft)
>
>
>
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