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
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