On Sun, 19 Jul 2009 10:13:03 -0400, Meat Plow
wrote:

On Sat, 18 Jul 2009 19:56:09 -0700, Jeff Liebermann
wrote:

On Sun, 19 Jul 2009 01:39:38 +0100, "Arfa Daily"
wrote:

That's interesting. I wonder what the perceived advantage of using circular
over linear polarisation is ?

Perception is everything, except in this case.

There are some technical advantages to CP. With a single LNB, it's
possible to install the dish with only elevation and azimuth, and no
consideration for tilt. However, with 2 or more LNB's, it is
necessary to align the dish tilt along the ecliptic.

US DTV HD dishes are now tilted but I don't recall this in the
beginning of their HD offering. Single/dual LNB are not tilted, at
least mine isn't and there is no aiming spec for it. US DISH network
has always tilted even with one LNB IIRC.

Dual LNB is a single LNB with two front end sections. It is aimed at
a single satellite and can feed two receivers, or a dual front end
receiver (i.e. DVR). A dish with two seperate LNB's, each with 2
outputs or 1 output going to a DISEqC switch, is a different animal as
it's designed to hear two satellites. I try to avoid using the term
dual LNB because it's ambiguous.

I've installed a few single LNB dishes. The dish alignment
instructions and web pages didn't have any provisions for tilt. Only
when multiple LNB dishes appeared was there any consideration for
tilt. It might also be useful to note that the single LNB dishes do
not have any mechanism for adjusting tilt.

With HD, one must see more than one satellite. As usual, Europe does
it with a mechanical DISEqC protocol rotator, while the US does it
with multiple LNB's. Each has their benefits and problems. I wasn't
paying much attention when HD first appeared, but I do recall that it
required a new dish because the feed came from a different bird.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558