P3D Re: polarization

[bob Wier <wier@xxxxxxxxxxxxxxxxx>]

>Light is the same as microwave as far as the way the E and M fields
>behave. There is a curious difference in custom. The definitions for
>right and left circular for microwave are the opposite of the
>definitions for light. 

    Wow! I didn't know that (learn something every day!).

>
>I would expect that circularly polarized signals reaching a linearly
>polarized antenna like a simple whip end up with a 3dB loss. Just as
>circularly polarized light loses 50% or 3dB or 2 stops when passed
>through a linearly polarized filter. 
>
>I would expect that circularly polarized signals reaching a circularly
>polarized antenna of the opposite type would result in an infinite loss.
>The same as passing circularly polarized light through a circular
>polarizer that is of the opposite handedness of the light.
>

After I posted that, I got to thinking as to whether it was
correct or not, ie. you get a 3db loss in

circular -> linear   mismatch
or
circular -> opposite circular mismatch

I think I may have been confusing this with the discussions that
occurred at the time that FM radio broadcasting first became
widespread (yeah, I'm that old). At the time most broadcast
band FM radios where horizonally polarized on the tower because
they figured most people were listening at home. Since most
auto antennas are vertical, you took a hit in signal strength.
I've not heard about that for several years. I wonder if normal
BC/FM transmitting antennas are still horizontal?

Most ham installations of FM antennas (especially repeater) were/are
done vertically on the basis that many people were using handheld
radios (vertical antennas) and whips on the autos at VHF. And thinking
about cell telephone antennas/towers, those *look* like they are 
vertical.

Thanks! de WB5KXH

-Bob Wier

       mailto:wier@xxxxxxxxxxxxxxxxx 
       4:10 AM Saturday, July 31, 1999
     Unix/Internet Systems Administrator
    Rocky Mountain College, Billings, MT
      (currently in Ouray, Colorado)



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