That I believe. Others have mentioned conditions that may be more likely to
occur at differing locations but I hadn't thought about the terrain
programs. The fact they do not consider ASL as part of the calculations
pretty much says it all. It would be interesting to hear from the author of
one of the terrain programs for his theory or reference information on it.
Anybody know one?
These are all factors that identify changes other than elevation of the
site:
Top of a mountain or hill - slope away from the antenna lowering angle of
radiation.
Mountain top may have rock that is quite reflective and conductive more like
salt water.
Seaside location - salt water, how lucky can you get.
Rural or sparsely populated location - low noise so you can hear ANYTHING.
Somebody mentioned VHF/UHF - of course - I should have specified HF for my
question.
I should have also specified the SAME antenna height above ground - simply
change in ground elevation
Thanks everybody for your answers. I think the fact the terrain programs do
not consider ASL as part of the calculations pretty much says it all. This
is the part where I get to pick out the answer I like the best and it
happens to fit with what I would be able to agree with.
tnx es 73, de Jim KG0KP
----- Original Message -----
From: "W3YY" <w3yy@cox.net>
To: <towertalk@contesting.com>
Sent: Friday, November 10, 2006 5:00 PM
Subject: Re: [TowerTalk] altitude
> Joe -
>
> With all respect to whomever did your terrain analysis...
>
> The antenna 400ft above flat terrain will have a vertical radiation
pattern
> characterized by many peaks and nulls, with the first peak at a relatively
> low takeoff angle. The antenna at 50ft over sloping ground will have its
> first peak at a higher angle than the first antenna, but usually at a
pretty
> useful angle and at perhaps at higher gain depending on the exact nature
of
> the slope.
>
> Good news for you, as now you don't have to build a 400ft tower!
>
> As far as I know, all terrain modeling programs consider local terrain,
not
> ASL per se. In otherwords, the same local topography at 5000 ASL produces
> the same result as that at sea level.
>
> 73, Bob - W3YY
>
>
> ----- Original Message -----
> From: "Joe Giacobello" <k2xx@swva.net>
> To: "Jim Jarvis" <jimjarvis@verizon.net>
> Cc: <towertalk@contesting.com>
> Sent: Friday, November 10, 2006 9:20 PM
> Subject: Re: [TowerTalk] altitude
>
>
> >I had asked a similar question several years ago. I had read that the
> > real height and ground effects of a horizontal antenna were really
> > determined by the ground and terrain 2-1/2 - 3 wavelengths from the
> > antenna. A ham, EE grad student and antenna specialist from Va Tech had
> > also commented that height combined with terrain that slopes off fairly
> > rapidly does a lot to enhance low angle reinforcement, if I remember
> > what he said correctly. Frankly, I was a little skeptical.
> >
> > However, since i live on a hilltop that's about 400' above the
> > surrounding land and slopes off, more or less, at a 45 degree angle, I
> > asked a contributor to this reflector who has expertise in the use of
> > terrain analysis programs, to compare a horizontal antenna 450' above
> > flat ground to the same antenna on a 50' tower on a hilltop like mine.
> > He reported that the radiation patterns were virtually identical. So if
> > the terrain is contoured properly vs the wavelength of operation, higher
> > elevations can be the equivalent of very high antennas over flat
terrain.
> >
> > 73, Joe
> > K2XX
> >
> > Jim Jarvis wrote:
> >> Jim,
> >>
> >> I've never seen any quantitative site studies supporting altitude as a
> >> dominant variable, unto itself. The answer probably depends more on
> >> other variables than just altitude. Like...does the terrain for 1-2
> >> miles
> >> gently slope down from the antenna site? Is the 3500' high site
> >> a wetlands?
> >>
> >> I had a simple 80m halfwave up about 85', adjacent to the
> >> Chesepeake Bay. 20' above sealevel. Played great.
> >>
> >> On the other hand, when K2BMI bought his place in NJ's
> >> Sourland Mountains, he used to say "there's rf
> >> up there, that never gets down to the flatlands". And,
> >> in fact, I heard openings from there I'd never heard before.
> >>
> >> So, unfortunately, your mileage may vary. I'd be interested
> >> to know if anyone is aware of such a study.
> >>
> >> n2ea
> >>
> >> Message: 5
> >> Date: Fri, 10 Nov 2006 09:22:23 -0600
> >> From: "Jim Miller" <JimMiller@STL-OnLine.Net>
> >> Subject: [TowerTalk] Altitude
> >>
> >> If this is too far off topic, one flame will do.
> >> OK, I understand the effects of and on
> >> 1. height of the antenna
> >> 2. angle of radiation
> >> 3. layout of the terrain in the near field
> >> 4. location surrounded by salt water vs. desert sand
> >> 5. etc.
> >> BUT: IS THERE A DIFFERENCE (if the same above conditions exist) whether
> >> the
> >> site is located
> >> at 300 ft or at 800 ft or at 1500 ft or 3500 ft? WHY? Tnx es 73, de
Jim
> >> KG0KP
> >>
> >>
> >>
> >> _______________________________________________
> >>
> >>
> >>
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> >>
> >>
> >>
> >
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> >
> >
> >
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