Diesel

Sky + has a QUAD LNB on the dish - i.e you can have four separate feeds off it. I dont think it is anything to do with polarisation?

Think of it as effectively separate feeds to the TV, to the Hard drive and another to the box in yer bedroom maybe. This leaves a spare feed in my instance - for further expansion! D

PS I thought it exceedingly clever last night to be recording two different programmes whilst playing another one back!!!

imlach

Incorrect. A Sky+ box needs two LNBs (and hence 2 cables) so that each LNB can be set to a different polarisation (ie, the Sky+ box has 2 demultiplexors/tuners) eg, BBC1 may be horizontally polarised, and Sky1 may be vertically polarised - your 3rd channel comes off either one or the other tuner.

How can I explain that better? Well, imagine your tv aerial. You only have one cable coming from that as it only receives 1 group of signals.

With Sky, channels broadcast from the satellite are either horizontally or vertically polarised. The polarisation is controlled in the LNB (pointy bit on your dish) with a voltage sent from your digibox. Therefore, to receive multiple channels at once, you need, in effect, two aerials (LNBs) to receive ALL the channels - hence the 2 x LNBs. One has to be set to receive the horizontally polarised multiplexed channels, and the other set to receive the vertically polarised multiplexed channels. Think of it like having to turn your tv aerial sideways to receive different channels!

They just put a quad LNB up there in the hope you WILL take a 2nd box on the 3rd LNB. Also, apparently dual-LNBs are not as reliable as quads for some reason, but that is just hearsay - I wouldn't know why.

Diesel

I think I'm starting to get it! So a quad LNB can feed one SKY+ and 2 standard boxes?

If you have a standard single input box, single LNB setup you can change the polarisation required 'electronically', but as SKY+ may demand either polaristation from either LNB at any time they both need to be able to switch to any polarisation. Actually that makes sense as if it wasnt the case 2 tuners could share the one input.

Phew!!

D

only ever have two usable outputs?

imlach

Diesel, yes, you've got it.

Yes, you can have 2 Sky+ boxes on a Quad LNB, or 1 Sky+, and 2 x normal boxes.