Polarization Questions
Robert11 wrote:
a. Anyone have any idea if a receiving
Discone type of antenna is Polarized
horiz. or vert. ?
It is vertically polarized over its entire
frequency range.
b. Same question for a Scantenna ?
If it is installed as usually illustrated with
the elements vertical, then, yes, it too is
vertically polarized.
c. On VHF and UHF scanner freq's, are the
(typically vertical, I believe ?) transmitted
polarizations from Fire and PD transmitters
usually maintained over distances of, e.g.,
10 miles or so ? Or does "bounce", etc., tend
to totally de-polarize them ?
Land mobile and aircraft radios almost invariably
use vertically polarized antennas. That wave
polarization is generally maintained under conditions
of reflection and refraction over short- and long-
distance paths. For polarization rotation to occur
during propagation, the medium generally must be
birefringent (eg: the ionosphere). This rarely occurs
with terrestrial waves.
d. If a receiving signal is well polarized in
one direction, say vertically, how much loss
would one expect if the receiving antenna is
oriented such that its preferred polarization is
horiz. ?
The usual figure one sees bandied about is 20 dB.
e.g., for a rubber-duckie scanner antenna ?
There's an additional penalty of 20 dB imposed on
any antenna that has the word "duckie" in its name.
;-) ;-) ;-)
Jim, K7JEB
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