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Re: [TowerTalk] HFTA and diferent bands antennas

Subject: Re: [TowerTalk] HFTA and diferent bands antennas
Reply-to: "Tower and HF antenna construction topics." <>
Date: Mon, 26 Apr 2010 08:22:06 -0400
List-post: <">>




-----Original Message-----
From: Jim Brown <>
To: Tower and HF antenna construction topics. <>
Sent: Sat, Apr 24, 2010 9:08 pm
Subject: Re: [TowerTalk] HFTA and diferent bands antennas

On Sat, 24 Apr 2010 17:52:53 -0700, jimlux wrote:

>I don't know about that... That would imply a violation of reciprocity, 
>wouldn't it?

Not necessarily. See below.

>I would believe non-symmetric propagation via skywave, but not that the 
>"effective antenna pattern" is different for transmit/receive.

The word "effective" is an important qualifier here. What HFTA does is 
attempt to model interaction of the wavefront with terrain. So it isn't 
the antenna pattern that's changing, it's the interaction with terrain. 
Intuitively it seems possible that wavefronts traveling in different 
directions might interact differently.  Or maybe not. :) I slept through 
that part of physics. 


Jim K9YC

Yes Jim, you did. When it comes to "pure" reflection you are dealing with the 
normal reciprocity.
When you are dealing with a wave traveling through a charged media interacting 
with a magnetic field,
 such as the ionosphere, now the reciprocity is no longer there.

Hans- N2JFS 


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