[opendtv] Re: MIMO
- From: "Cliff Benham" <flyback1@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 30 Apr 2007 19:20:05 -0400
So perhaps the practical reasons no right-hand or left-hand circularly
polarized
UHF transmitting antennas are in use is that:
1. The antennas would be much more expensive.
2. The antennas are highly directional requiring arrays of more of them for
equal
signal coverage than could be had with conventional vertical-horizontal
or eliptical
antennas.
3. Larger power bills because more power is required because there are more
antennas in the array.
One comment I do not understand is that the signal from a LH or RH Circ.
Pol. antenna system
would be more easily picked up with a conventional indoor bowtie, loop or
rabbit ear antenna.
Is this because of the higher transmit power made necessary by the greater
number of radiators
in the array or some characteristic of the RH or LH circ. signal
polarization?
Cliff
Dale,
How is it possible to have a circularly polarized omnidirectional signal?
You can have a dual horizontal and vertical polarized high power UHF
television transmission antenna, which is what passes for "CP" in the
broadcast world, (or if the power ratio is not 1:1 it is called "elliptical"
as you correctly pointed out,) but you never see a spec in the Dielectric or
Andrews (R.I.P) catalogs for a "Left Hand" or "Right Hand" circular
polarization of their UHF antennas. They just list the horizontal to
vertical ratio.
DBS uses a true circular polarization, as does some forms of radar, but in
both cases the radiation is highly directional.
John
----- Original Message -----
From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
>
> 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.
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