[TowerTalk] altitude

[W3YY]

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 at swva.net>
To: "Jim Jarvis" <jimjarvis at verizon.net>
Cc: <towertalk at 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 at 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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