Does AFN use RHCP or RHEP ?

Vipersan

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A question relating to the hit n miss nature of AFN at 1west which we questioned some while back ..
That there is something odd about this signal in relation to other Circular broadcast transmissions..
I have done some reading up on just how the vectors relate to each other during rotating or circular fields..
We all know that dielectric materials placed at 45 degrees to the H and V probes in a voltage switched LNB depolarise or convert signals to a useable H and V ...and this is achieved by delaying one field ie the H or V component by 1/4 rotation...
Odd then that a dielectric plate placed first at exactly 45 degrees to a correctly orientated lnb will produce lockable results from both AFN and BBC Africa (Both RHCP) ...and the same plate rotated by only a couple of degrees + or - 45 degrees makes little difference to BBC Africa ...and practically no difference to AFN rotated anticlockwise ...but the same difference clockwise makes the signal unlockable..
I never questioned this until I read of the possibility of transmissions with one field greater in amplitude during vector rotation ...ie elliptical polarisation RHEP ...or it's counterpart LHEP..
Apparently postulated for terrestrial communications with mobile phone networks as having a greater V to H component could have better penetrative properties through structures ...
Maybe I'm posting absolute crap ..
..and just thinking out loud..
rgds
VS
 

Channel Hopper

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Since most satellites do not have a ground footprint where the the two linear planes of transmission appear at 90 degrees to each other, the circular polarisations would logically follow. To depolarise them for entry into the throat of an LNB however is not within the bounds of a dielectric type, and you would almost certainly require a mechanical filtering system to achieve it.

Elliptical polarization

Elliptical polarization results when one of the two linear components in CP is greater amplitude than the other. The ratio of the two voltage amplitudes is called the axial ratio. When axial ratio is one, you have CP.


One way to look at elliptical polarization is that the two components of circular polarization are not exactly 90 degrees apart.


http://www.microwaves101.com/encyclopedia/polarization.cfm
 

Vipersan

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Fair enough CH ..
Just trying to account for the slightly odd behaviour of this one RHCP channel..
I had read that Elliptical polarisation was indeed adopted by the military ...hence my leap of faith on this ..
I also read somewhere that Elliptical polarisation might be used to counteract Satellite variances ..such as wobble and back in the day 'spinners'..
cheers buddy.
 

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It could be, but unless you have one of these onboard (c-band demo),


you are unlikely to find out.

As 'not our Rolf' said - 'Can you see it yet ?'



If you search using the colonial English 'polarizer' all becomes clear.
 

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Last video is an eye opener.
 
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