[TowerTalk] ionosphere and ground reflections of radio signals

[hanslg at aol.com]

 Hi Al,

The bending of the waves in a "charged media" is do to the interaction between the charges and the wave (not the magnetic field) and (I believe) reciprocal. When you add a magnetic field you get a change in polarization. This polarization change is not reciprocal. You see that same phenomena in circulators and directors, you know, those peculiar items there the signal goes through in one direction with minor damping but major attenuation in the other direction.

I don't think an antenna book is the right place to find the phenomena explained. A book in electro-dynamics/plasma physics is a better place. (Yes, I slept through the classes when this was explained in greater details).

The reflection in the ionospheric is similar (but not the same) to the total reflection when a wave enter from a high density media to a low density media. A charged media can be viewed as a dielectricum with a dielectric constant (or refraction index) smaller than 1 (strange thing but that's the way to think about it). The "mirror" model is easier to picture but is more limited than the <1 refraction index media. You can try to imagine that the radio wave has to penetrate the ionosphere a bit before the "reflection" takes place. If the charge density is not high enough of the ionized layer not thick enough the wave will go through with out reflection. 

I have to dig out my books in physics and check further (after dusting them off big time, when I get the time:-).

73

Hans - N2JFS

 


 

 

-----Original Message-----
From: Al Williams <alwilliams at olywa.net>
To: towertalk at contesting.com
Sent: Mon, Apr 26, 2010 11:04 am
Subject: [TowerTalk] ionosphere and ground reflections of radio signals


> 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

I can't recall, in the dozen or so books on antennas etc. that I have, an 
explanation of the reflection mechanism.  Maybe it is in there in the math 
but not in more simple terms. I vaguely remember, but not where I read it, 
that the traveling wave into a ionosphere media gets bent because of the 
action of the wave on the existing electrons (or atoms?). But is it because 
of the electric or magnetic field? And what about the reflection from the 
ground --electric, magnetic field, horizontal or vertical polarization, 
etc.Why is the exit angle identical to the entrance angle.

Understanding radio waves and propagation is a rather challenging and slow 
process for me. It doesn't help to simply state that the action is identical 
to light rays!

k7puc 

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