Em Smith wrote:
> Ah, I get it now. So the unicable LNB is a quad and all four "signals" come down the same cable (high/low/vertical/horizontal or whatever the naming is) and can only come to one box. A bit like a tv aerial. The box then has the magic to demultiplex it to four internal tuners. Actually, I see there are unicable splitters but that would mean if I split two "signals" to my set-top-box the Digibit can only use the other two and not use all four of its internal tuners or would risk contention with the STB.
Actually - I can see why you'd think that, but that isn't how Unicable and Unicable II work.
Normal Universal LNBs send one of four very wide band range of signals down the LNB cable (High Frequency or Low Frequency, Horizontal or Vertical polarisation). Which of the 4 IF band options that is output by the LNB is remotely controlled by the tuner (using a combination of voltage switching for H/V polarisation and 22kHz tones for Hi/Lo). The tuner then tunes across this very wide IF band (~950-2200MHz) to select a single transponder which is usually something like 27-36MHz wide. This 4 way switching is why historically each tuner has needed its own LNB cable.
Unicable LNBs take a totally different approach. Rather than sending an entire ~1300MHz band down the LNB cable at once - to a tuner that only needs ~36MHz of it at anyone time, instead the LNB allocates fixed frequency 45MHz wide (I think) channels to each tuner connected to the LNB. To tuner a particular transponde the tuner then sends a precise request for the transponder frequency it wants to the LNB, which then transposes just the 45MHz wide band at the transponder frequency requested and shifts this to the fixed frequency band allocated to that tuner. So rather than just asking for one of the 4 Universal LNB bands, it asks very specifically - using data a bit like Diseqc and Hi/Lo switching - for a very specific transponder frequency and polarisation to be sent in the 45MHz RF block allocated to it.
This is far more efficient - but it does require that the LNB (or mulitswitch - you can implement it this way too) is more complex (crudely it needs a local oscillator for every tuner rather than just two). It also requires that the receiver/tuner is Unicable compatible - and knows to send data to the LNB to change transponder, not to tune across the LNB IF range itself.
Unicable I supports 8 tuner channels - so one cable can carry feeds for up to 8 tuners. Unicable II supports up to 32 tuner channels, so can support 32 separate tuners via a single cable.
However you need Unicable compatible hardware and software I believe for this to work or a Unicable compatible set top box.
* SKY+ HD UK boxes are NOT I believe Unicable compatible. Sky have a system called SCR to do something similar - but not the same. Sky Q boxes DO use Unicable optionally I believe - though their default install is again a different type. They use two LNB feeds with wider bands than a normal Universal LNB - so each cable carries either a full Horizontal or full Vertical band - with no need for Hi/Lo switching*
>
> Whereas a quatro LNB I would have four cables coming down to the living room and then a powered switch there to feed as many boxes as I want (such as 16 on the one switch I saw), with one cable for each tuner, so four cables to digibit and two to STB with no contention since the switch does the magic. And a quad LNB is four cables and can feed up to four boxes and no more, so two to STB and two to Digibit.
Yes - a Quattro (or a Quad with some multiswitches which permanently drive the Quad outputs into HiH, LoH, HiV, LoV - though there are pitfalls potentially with this approach) would let you feed multiple tuners too. Unicable is neater - but requires compatible tuners. Multiswitches look just like a Universal LNB to the device they are connected to, so need nothing clever in the tuner.