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Re: [TowerTalk] Takeoff Angles and Non-Reciprocal Propagation

To: xdavid@cis-broadband.com, towertalk@contesting.com
Subject: Re: [TowerTalk] Takeoff Angles and Non-Reciprocal Propagation
From: TexasRF@aol.com
Date: Thu, 1 Nov 2007 17:29:08 EDT
List-post: <mailto:towertalk@contesting.com>
 
I have not modeled this and wonder if there is any prediction of added  
losses when refraction is utilized?
 
73,
Gerald K5GW
 
In a message dated 11/1/2007 4:26:51 P.M. Central Daylight Time,  
xdavid@cis-broadband.com writes:


HFTA  clearly shows that signals can be refracted over sharp terrain 
features to  bend closer to the horizon (sometimes significantly so) than 
would  otherwise occur based upon the actual antenna height above 
ground.   Some portion of the transmitted signal might end up with an 
effective  takeoff angle of, for example, six degrees that wouldn't be 
there without  a fortuitously located hill.  Since terrain features are 
almost never  symmetrical, though, there doesn't seem to be any guarantee 
that a return  signal from the DX end would necessarily bend back down to 
the local  antenna, at least not in exactly the same way.  I would think 
that  the sharper side of a hill would defract a signal differently than 
a  gently rounded side.

I wonder if this could possibly explain some of  the non-symmetrical 
"propagation" that most of us think we may have  occasionally 
experienced.  I would think even a large building of the  right shape and 
composition could act like a terrain feature ...  especially on the 
higher frequency bands.

Dave    AB7E

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