[opendtv] Re: MIMO
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 30 Apr 2007 14:21:05 -0700
John wrote:
> P.S. To be clear, many UHF broadcast antennas have both horizontal and
> vertical properties. The FCC measures maximum ERP only in the
> Horizontal plane, and usually broadcast antennas have much less
> energy in the vertical than the horizontal. This is still called
> Circular Polarization.
This is actually known as elliptical polarization. Many antenna do use a
degree of elliptical Pol. and off handedly it is sometimes called CP.
However, there are also a number of true CP installations, though I believe
that elliptical is clearly in the majority and they do also improve
reception but to a lesser degree. It's an economic trade off.
> -----Original Message-----
> From: opendtv-bounce@xxxxxxxxxxxxx
> [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of John Shutt
> Sent: Monday, April 30, 2007 1:12 PM
> To: opendtv@xxxxxxxxxxxxx
> Subject: [opendtv] Re: MIMO
>
>
>
> ----- Original Message -----
> From: "Cliff Benham" <flyback1@xxxxxxxxxxx>
>
> >>TANSTAAFL.
> There Ain't No Such Thing As A Free Lunch
> - Robert Heinlein "The Moon is a Harsh Mistress"
>
> > ISBIDKWTM.
> (I Searched But I Don't Know What That Means?)
> Google is our friend:
> http://www.google.com/search?hl=en&q=TANSTAAFL
>
> John
>
> P.S. To be clear, many UHF broadcast antennas have both horizontal and
> vertical properties. The FCC measures maximum ERP only in the horizontal
> plane, and usually broadcast antennas have much less energy in
> the vertical
> than the horizontal. This is still called Circular Polarization,
> but it's
> more like dual polarization, and with the power differential,
> it's more like
> Oval Polarization.
>
> DBS satellites use CP, real CP, with a left hand and right hand.
> Most C and
> Ku satellites used horizontal and vertical polarities, which requires not
> only the proper azimuth and elevation of the receive antenna, but a very
> critical polarization adjustment as well.
>
> With DBS satellites, you only need the proper vertical and horizontal
> directions to receive the desired satellite, but since the polarity is
> circular, the tilt of the satellite dish is non critical. It could even
> work upside down!. Left hand is still left hand, and RH is still RH.
>
> That said, the newer DBS dishes that look at two or three satellites
> simultaneously with a corresponding number of offset feedhorns have
> reintroduced the requirement to get the horizontal plane of the
> dish correct
> in order to properly see the desired satellites in the Clarke belt.
>
> John
>
>
>
>
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