Polarization - Techwatch: Satellite TV forums, FTA, Cable, Hardware, & Tech forums

imported_Jimbo · 08-03-07, 07:07 PM

Hi,

Now this may seem a dumb question (and I promise I have tried searching for the answer)... but...

If I have a motorised dish (h-h motor) how does the polarization get altered as the dish locks on to the various satellites (using the free SMWlink software I get varying polarization values for a range of sats).

On a static dish I would only have to worry about one sat per lnb so the rotation of the lnb (polarization?) would be sorted manually as a one off adjustment.

Thanks
Jimbo

Jimdefruit · 08-03-07, 07:27 PM

The polarisation is either vertical or horizontal and it is to do with the transponders and not the satellites.

If you look at a transponder list for say Astra 1 19.2 east, you will see a list of frequencies. Some are horizontally polarised and some are vertically polarised. Your receiver actually switches the LNB to select the polarisation for a particular transponder.

imported_Jimbo · 08-03-07, 08:27 PM

Ok,

ops:

Told you it was dumb - what I was actually thinking of is the amount you twist the lnb for each satellite. I have read here that sometimes this needs to be done to get the best signal on a static dish, my question is how would you overcome this (on as motorised system) when it could need a different amount of rotation for each satellite the dish is focused on - or do you just pick the weakest satellite it will be used and compensate for that one? or do you just ignore it?

Or am I completely confusing myself and all others :

:?

Thanks again.
Jimbo

Jimdefruit · 08-03-07, 09:16 PM

The actual motor mount is angled so that the axis changes as the motor turns.

BGonaSTICK · 08-03-07, 11:53 PM

Here's a recent thread taking about motors and 'skew':

http://www.satellitehelp.co.uk/forum...ic,3981.0.html

BlackHawk · 09-03-07, 12:54 PM

Hi Jimbo

Sometimes a picture saves a thousand words
Pic 1 is my dish at 58 degrees west
Pic 2 is my dish at 53 degrees east.
As you can see the motor moves the dish so that it, and hence the lnb, are aligned to the vertical and horizontal signals coming down from the satellite.
BH

BGonaSTICK · 09-03-07, 02:10 PM

Those two pictures really demonstarate the effect very well

imported_Jimbo · 09-03-07, 05:23 PM

Hi all,

Now I get it

I never realised that the motors pivoted that way.

When I started the thread I had never had a close up look at a motor.

..but...

I got the first real look at one when my diseqc arrived just now

I wouldn't have initially guessed (without looking closer) that the angled mount would produce that effect on the dish, but a little moments thought and it is quite apparent.

Thanks for beating it home guys, just need the rest of my goodies to arrive now.

Jimbo

08-03-07, 07:07 PM	#1 (permalink)
imported_Jimbo Junior Member Join Date: Mar 2007 Posts: 18 Thanks: 0 Thanked 0 Times in 0 Posts	Polarization Hi, Now this may seem a dumb question (and I promise I have tried searching for the answer)... but... If I have a motorised dish (h-h motor) how does the polarization get altered as the dish locks on to the various satellites (using the free SMWlink software I get varying polarization values for a range of sats). On a static dish I would only have to worry about one sat per lnb so the rotation of the lnb (polarization?) would be sorted manually as a one off adjustment. Thanks Jimbo

08-03-07, 07:27 PM	#2 (permalink)
Jimdefruit Super Moderator Join Date: Jan 2006 Posts: 2,775 Thanks: 10 Thanked 113 Times in 105 Posts	Re: Polarization The polarisation is either vertical or horizontal and it is to do with the transponders and not the satellites. If you look at a transponder list for say Astra 1 19.2 east, you will see a list of frequencies. Some are horizontally polarised and some are vertically polarised. Your receiver actually switches the LNB to select the polarisation for a particular transponder. __________________ Dreambox 800 HD; Dreambox 7000s + VBox + Channel Master 1.2 with 36v actuator CM120 feedhorn and Invacom .3 LNB Skystar 2 PCI card with links to my Dreambox If you like what you see here, tell your friends.

08-03-07, 08:27 PM	#3 (permalink)
imported_Jimbo Junior Member Join Date: Mar 2007 Posts: 18 Thanks: 0 Thanked 0 Times in 0 Posts	Re: Polarization Ok, ops: Told you it was dumb - what I was actually thinking of is the amount you twist the lnb for each satellite. I have read here that sometimes this needs to be done to get the best signal on a static dish, my question is how would you overcome this (on as motorised system) when it could need a different amount of rotation for each satellite the dish is focused on - or do you just pick the weakest satellite it will be used and compensate for that one? or do you just ignore it? Or am I completely confusing myself and all others : :? Thanks again. Jimbo

08-03-07, 09:16 PM	#4 (permalink)
Jimdefruit Super Moderator Join Date: Jan 2006 Posts: 2,775 Thanks: 10 Thanked 113 Times in 105 Posts	Re: Polarization The actual motor mount is angled so that the axis changes as the motor turns. __________________ Dreambox 800 HD; Dreambox 7000s + VBox + Channel Master 1.2 with 36v actuator CM120 feedhorn and Invacom .3 LNB Skystar 2 PCI card with links to my Dreambox If you like what you see here, tell your friends.

08-03-07, 11:53 PM	#5 (permalink)
BGonaSTICK Super Murderator Join Date: Nov 2005 Location: Brighton Posts: 10,633 Thanks: 3 Thanked 64 Times in 37 Posts	Re: Polarization Here's a recent thread taking about motors and 'skew': http://www.satellitehelp.co.uk/forum...ic,3981.0.html __________________ Dreambox 7000, Skystar2 PCI, Skystar USB, Fibo 90cm on Moteck SG2100, Triax TD110 multi-LNB. Sky + ART cards. 45.0°E - 58.0°W


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09-03-07, 12:54 PM	#6 (permalink)
BlackHawk Satellite Help member Join Date: Nov 2006 Location: Suffolk, ENGLAND Posts: 169 Thanks: 2 Thanked 5 Times in 5 Posts	Re: Polarization Hi Jimbo Sometimes a picture saves a thousand words Pic 1 is my dish at 58 degrees west Pic 2 is my dish at 53 degrees east. As you can see the motor moves the dish so that it, and hence the lnb, are aligned to the vertical and horizontal signals coming down from the satellite. BH __________________ Smart 0.2dB LNB, 1m Gibby dish, Stab HH100 motor, 10m co-ax, TM1000D, TM1500CI+super & TM 5200D USB boxes (modified). 57east to 61west.

09-03-07, 02:10 PM	#7 (permalink)
BGonaSTICK Super Murderator Join Date: Nov 2005 Location: Brighton Posts: 10,633 Thanks: 3 Thanked 64 Times in 37 Posts	Re: Polarization Those two pictures really demonstarate the effect very well __________________ Dreambox 7000, Skystar2 PCI, Skystar USB, Fibo 90cm on Moteck SG2100, Triax TD110 multi-LNB. Sky + ART cards. 45.0°E - 58.0°W

09-03-07, 05:23 PM	#8 (permalink)
imported_Jimbo Junior Member Join Date: Mar 2007 Posts: 18 Thanks: 0 Thanked 0 Times in 0 Posts	Re: Polarization Hi all, Now I get it I never realised that the motors pivoted that way. When I started the thread I had never had a close up look at a motor. ..but... I got the first real look at one when my diseqc arrived just now I wouldn't have initially guessed (without looking closer) that the angled mount would produce that effect on the dish, but a little moments thought and it is quite apparent. Thanks for beating it home guys, just need the rest of my goodies to arrive now. Jimbo