Towertalk
[Top] [All Lists]

Re: [TowerTalk] Polarization change Was ( Gizmotchy's)

To: Michael Ryan <mryan001@tampabay.rr.com>
Subject: Re: [TowerTalk] Polarization change Was ( Gizmotchy's)
From: Michael Keane K1MK <k1mk@alum.mit.edu>
Date: Fri, 10 Apr 2009 11:44:29 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 4/9/2009 2:05 PM, Michael Ryan wrote:
> I remember reading a study back some years ago about the benefits or lack
> there of, in using a vertically polarized antenna as oposed to a
> horizontally polarized antenna for long distance work. It read that there is
> little significant difference between the two at the recv end as the F2
> layer influences ( for lack of a better word and my memory) change these
> signals into primarily horizontally polarized signals anyway.  Does it make
> sense? Anyone have thoughts on that?  -Mike

It's not that the ionosphere preferentially converts a vertically 
polarized wave into a primarily horizontally polarized wave. In general 
the ionosphere doesn't do anything like that.

It's that the ionosphere randomly rotates the wave's plane of 
polarization. A vertically polarized wave incident on the ionosphere may 
come out as a horizontally polarized wave or it may come cut as a 
vertically polarized wave or, the far most likely case, it comes out as 
a wave polarized at some random angle in between horizontal and vertical.

So it's essentially impossible to "match" polarizations on ionospheric 
circuits.

The clear benefit in using horizontally polarized antennas is that 
orientation usually provides +6 dB or more gain relative to the same 
antenna with a vertical orientation. This advantage is the combination 
of ground reflection gain for the horizontal) and ground reflection 
losses (pseudo-Brewster angle) for the vertical.

The exception is of course when you can't place a horizontally polarized 
antenna high enough in terms of wavelengths, which typically is the case 
at lower frequencies.

73,
Mike K1MK
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>