Sky digital, two boxes one dish?

[T i m]

Hi All,

If you wanted to have two boxes from one Sky digital mini dish (?) would you need two LNB's (or a dual LNB) and two feed cables or do they do summat clever (splitting the cable indoors etc) these days?

All the best ..

T i m

[daddyfreddy]

My other satellite boxes have an output which you can feed into another reciever, can't remember if my Sky box has it though. Have a look on the back of yours.

[Colin Stamp]

You'll need at least a dual LNB, otherwise you'll find that there are a lot of combinations of channels on the two boxes that won't work.

The first stage of tuning is done by the LNB, and it will need to work in one of four different modes depending on what channel the box tries to display. If two boxes need two different modes, you're knackered with a single LNB.

Cheers,

Colin.

[T i m]

Ah, thanks (vertical / horizontal polarization n that?).

When I installed 15 of so Maspro systems for the friends / family (some years ago now) they used some 'figure of 8' cable with the co-ax for the video and a pair for the polarizer. It seems it's all done via a single co-ax now?

All the best Colin ..

T i m

[T i m]

Ah, I don't actually have Sky myself but a general question that came out of a conversation I was having with a mate earlier.

It was sorta along the lines of 'if we are running cables through the (soon to be sealed (as in access)) roof gap should we run one or two' .. ;-)

All the best ..

T i m

[Colin Stamp]

Yep. There's the two polarizations, and also two frequency bands, so four combinations in-all.

The box signals which polarization it wants by varying the LNB power-supply voltage, and it changes the frequency band by sending a

22KHz tone up the co-ax.

Cheers,

Colin.

[Dave Liquorice]

Two cables from the LNB. Voltages and tones are used to switch between hi/lo band and vertical/horizontal polarisation. Bit tricky to do within one cable.

The Sky box has two RF outs that you can use to feed other TV's but everything gets the same signal, no wtach one Sat station on one TV another sat station on a different TV.

[Andy Hall]

The Astra 2 satellite transponders operate such that LNBs need to be switched into four possible settings in order to achieve access to all channels. The frequency band is divided into two (high and low band) and vertical and horizontal polarisation is used as well.

The Sky Digiboxes signal the choices to the LNB through a combination of voltage and tone signalling through the cable. Thus, as you select channels from the EPG, the correct combination is set up on the LNB to pick the right frequency range and polarisation.

More generic DVB-S receivers usually offer a choice of this and a digital signalling method called DiSEqC

This signalling arrangement is the reason that you can't use simple splitters for satellite connections as you would for a TV antenna.

There two basic solutions that can address this if you want more than one receiver.

a) Dual LNB. This is essentially similar to the single LNB that you have already but with two separate outputs, each individually controllable. For this one, you have to home run the CT100 cable to each satellite receiver position from the dish. There are four-receiver versions of this known as Quad LNBs - however,

4 is the limit. Both will work with the Sky Minidish.

b) Multiswitch. This is an electronic switching unit which is usually fitted inside the house and sits between the receivers and the LNB. A specific type of LNB known as a Quattro (not to be confused with Quad) is used. These have four outputs with one carrying one of the four combinations (i.e. Vert. Low band, Vert Hi Band, Horiz Low Band, Horiz High Band). Thus the multiswitch has all combinations available. It understands the voltage and tone or DiSEqC signals from receivers and switches through the appropriate LNB output. There is some amplification to compensate for the signal losses. Think of it like a matrix. The advantage with this approach is that you can have quite a lot of outlets if you want the flexibility of more than two receivers, or more to the point, more than two outlets.

Most multiswitches also have an option to include signals from terrestrial antennas as well by having a 5th input. This is essentially a cabling convenience for if you want to distribute this as well. At the outlet positions, you fit a two or three way filter to separate the satellite signals from terrestrial.

The basic switches are not that expensive - e.g. an 8 way Triax one is about £100.

can be larger in terms of ways and also inputs. For example, I have a Spaun multiswitch with 9 inputs and 12 outputs (expandable if I wanted it). This has the ability to take inputs from two satellite dishes and deliver to the outputs. I have an Astra 2 (Sky) dish (slightly larger than the standard one) and a larger motorised dish which can be directed to most satellites with some level of footprint over the UK (Atlantic to quite a way East). The switch can select which dish should be used for a given selected programme from the EPG using DiSEqC signalling. AFAIK, the Sky boxes don't use this, so the default is arranged to be the fixed Astra 2 dish. I then have a DVB-S receiver which is able to both select the dish to be used and drive the positioner on the movable dish. Thus one can select which satellite and which programme from the EPG.

Personally, I like to be able to watch news and documentary programmes from other European countries, although most people probably don't. Another simpler solution for that is to fix two LNBs onto one dish based on the principle of the different positions of the satellites in space.

Quite a lot of choices depending on what you want to achieve and how flexible you want it to be.

[T i m]

Indeed there are!

Thanks very much for all the answers guys and especially to Andy for all the extra info (and I understood it!) ;-)

I think the dual LNB'svia two cables into two boxes is the solution to my post but the other options may be of interest in the future .. ;-)

I love 'kit' and some of my most enjoyable moments have been unpacking and neatly installing a few hundred grands worth of someone elses gear into 19" racks and making all the pretty lights flash .. (mainly voice / data datacomms > lan / wan). ;-)

All the best ..

T i m

[Colin Stamp]

Another thought!

If either of the boxes are Sky+, then you'll need extra LNB outputs - Sky+ boxes need two LNB feeds each.

Cheers,

Colin.

[Andy Hall]

True.

For Tim's application, using a Quad LNB is probably the best option, with the fourth cable run into the loft (if nowhere else) for future use.

[Dave Liquorice]

I agree, fit a quad the you have at least two spares for future expansion. 8 output LNBs are available (need an adapter for a sky wok though) but that's one heck of a bundle of cables. Much better to go quattro and switch if you think that number of outlets is likely to be required.

eBay seems a reasonable source of LNBs, just got a new Thomson quad for under 12 quid delivered.

[T i m]

Hmmm,

So, if he wants 2 x Sky digital boxes he'll need a 'quad' LNB?

I assume the '+' gives the ability to record a chan in the background so there are two tuners (decoders?) in there and hence the two feeds required?

Two Sky + boxes = 4 cables (2 to each box). ?

All the best ..

T i m

[Andy Hall]

Yes. Or at that point, a multiswitch starts to make more sense.

Yes. In essence, it's two receivers, but the operation is pretty much seamless and hidden behind the EPG and remote.

Yes.

With a multiswitch, you would still need two cables from the outputs of course.