Hi guys,
I'll be in Dublin between 22-26 January and looking forward to meeting some
of you there and roll some beers down...
Anyone interested?
73 de Zoli HA1AG
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>From Leigh S. Jones" <kr6x@kr6x.com Sat Jan 13 02:37:26 2001
From: Leigh S. Jones" <kr6x@kr6x.com (Leigh S. Jones)
Subject: [CQ-Contest] Local Terrain effect
References: <76.6caab1a.278ff9c8@aol.com>
Message-ID: <0db301c07d09$c494d600$ede3c23f@kr6x.org>
Using K6STI's "Terrain Analyzer" or "TA.exe" software I generated a couple
of views of vertical antenna performance for MW5EPA in answer to his
original question that started this thread on the reflector. I thought it
was worthwhile to pass the graphics along to the rest of the crew on the
reflector.
Using parameters for fairly high ground conductivity with moist soil, and a
10 meter vertical dipole up a half wavelength on the left half of the
radiation pattern, and on the right the same antenna and soil conditions on
a 700 foot high extreme mountain over a flat plain:
http://www.kr6x.org/image51.gif
Substituting parameters for salt water ground using the same antennas and
mountain (or no mountain): http://www.kr6x.org/image52.gif
----- Original Message -----
From: <W1HIJCW@aol.com>
To: <bjk@ihug.co.nz>
Cc: <cq-contest@contesting.com>
Sent: Thursday, January 11, 2001 10:10 PM
Subject: [CQ-Contest] Local Terrain effect
>
> Local Terrain -- the most valuable asset your station and antenna can
have!!
> :>)
>
> Seriously, I was led to some analysis of local terrain (out from 6 to 15
Km
> from the antenna) by the fortunate circumstance of having a QTH which was
> located on a ridge top which afforded me a very strong signal from
southern
> California into Europe using 100 W from a TS940 and a classic coax fed
dipole
> on 20 meters. Experimentation demonstrated that antenna height above local
> terrain was critical.
>
> In my case the antenna was sited on a roof top (about 1 meter above the
roof
> and about 8 meters above the ground level immediately below the antenna)
and
> broadside to approximately 020 degrees true, the great circle bearing to
> northern and central EU. Experiment showed that I could often open and
close
> 20CW to EU from the location even though 100W and a dipole would make that
> extremely unlikely.
>
> I did some analysis with several programs and topographic maps which
> indicated that the height produced approximately 9 dBd gain over a dipole
> located at the same height above flat ground. MORE IMPORTANTLY, the
elevation
> pattern of the antenna showed that the peak gain in the vertical plane
> occurred at an angle of between 1 and 2 degrees above the nominal horizon.
To
> achieve the same result over flat ground the antenna would have had to
have
> been at a height of more than 30 meters.
>
> On the bearing in question the average down slope was approximately 12 to
15%
> for a distance of about 1/2 Km, and continued at an average of 4 to 5%
down
> for another 3 to 4 Km before flattening out.
>
> In the reverse situation, I was able to use a club station here in
southern
> California for the 1999 CW sweepstakes. Power was 1500W and the antenna
was a
> seven element log periodic at a height of just about 40 meters (130 feet)
> above level ground. My experience (about which I wrote to the reflector
back
> then) was that such a height above average terrain was way too high for a
> domestic contest. My hypothesis was (and is) that the resulting low angle
of
> radiation placed the first return point of the refracted energy somewhere
in
> Ohio (which was OK) but put the second return point somewhere near
Greenland
> (not OK for a domestic contest). The result was that I seemed to work
every
> possible station in Ohio, but I had a hard time hearing (and being heard
by)
> stations in W1, W2 and W3.
>
> So the bottom line is that "higher or lower?" isn't a complete question.
One
> has to ask higher or lower for what purpose. And always keep in mind that
> higher or lower should be measured using what's often called HAAT (height
> above average terrain) which is usually considered to be that out 5 to 10
Km
> from the antenna, but in any case a minimum of 20 to 30 wavelengths.
>
> The best treatment of the whole subject is by N6BV in recent editions of
the
> ARRL Antenna Book and some editions of the Antenna Compendiums(ia)
>
> Cheers/73
> de Bill, W1HIJ/6, FO0SCH
>
>
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>
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