[opendtv] Re: MIMO

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 30 Apr 2007 16:11:43 -0400

----- Original Message ----- From: "Cliff Benham" <flyback1@xxxxxxxxxxx>

There Ain't No Such Thing As A Free Lunch
- Robert Heinlein "The Moon is a Harsh Mistress"

(I Searched But I Don't Know What That Means?)
Google is our friend:


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.


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