> From: Peter Chadwick <Peter.Chadwick@gpsemi.com>
Hi Peter,
(Woops, I changed software and I had my amps icon posting to topband!
But that's ok, my topband was going to my sister. I guess I'll get a
lump of coal for Christmas since I used to keep her AM radio wiped
out during high school with 160 QRM, so she hates topband.)
You have struck at the core of why all the chattering about the
polarization shift of the ionosphere is unimportant to most of us.
> Are most DX signals predominantly vertically polarized on arrival, or at
> least slant polarised by being slowed down at the air-ground interface,
> or possibly even elliptically polarised?
The polarity is nearly never perfectly vertical or perfectly
horizontal, and it is traditionally accepted it slowly shifts back
and forth.
Near the ground ALL low angle signals are near vertical polarized for
ONE simple reason, the ground itself cancels or greatly attenuates
all lower angle horizontal signals.
The earth effectively short circuits the horizontal electric field,
and so the magnetic field also must also be effectively removed.
It's only the high angle signals that can be near-horizontal,
unless the antenna is several hundred feet in the air on 160.
> Are skewed path signals more or less the same as above in polarisation?
No one probably really knows, because there is next to no data on
this subject for 160 meters and even 80 meters. The reason for the
near-total lack of hard data is simple, the experimenter would need a
helicopter or airplane to measure the true optimum polarity.
The sense antenna would have to be high enough to be in the
far-field of earth, otherwise he'd simply be measuring the
predominant effect of earth near the antenna and the much less
dominant distant ionosphere.
The problem near earth is more one of wave angle than polarity. If I
had a 350 ft tower, I'd be concerned with polarization. With a 130 ft
tower, I care less what the polarity is for signals below 30 degrees
elevation.
73, Tom W8JI
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