P3D Re: OT broadcast polarization

[Rob <lilindn@xxxxxxxxxxx>]

>
> Broadcast radio FM is still horizontally polarized.

 Actually, Most FM broadcasters in North America are Circular.  By FCC (USA) law, all FMs must
broadcast horizontal component (exception - a few FMs near the bottom of the band protecting
adjacent TV channel 6), and can also use vertical component if it does not exceed the
horizontal (if the vertical component is equal to the horizontal and is 90 deg out of phase,
the result is circular polarization), most are circular, as it improves reception on portables
and helps reduce the effects of multipath.



> Same for TV sound
> signal which is FM.

  AFAIK, the polarization of the aural carrier is whatever the station uses for the video.


> Broadcast radio AM and TV vieo which is AM are
> vertically polarized.

   The Video of TV in N.A. has **never** been vertical polarization,  traditionally always
horizontal - regular TV broadcasting with anything other than horizontal was illegal in USA
until the late 1970s.  Although any TV station can use circular or elliptical (less energy in
the vertical than the horizontal) polarization, relatively few do, most figure its a waste of
electricity.  Many Low-Band (chs 2-6) stations in major markets are circular - it improves
reception on portables - Low banders usually don't come in that well on portables.
     AM broadcasters do use vertical only - not because of the AM modulation mode, but because
the "soil" groundwave propagation that allows such long waves to be carried over a distance
during the day requires vertical polarization,

     Rob
     "Everything I have is Y1.96K compliant"


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