Sky+ and TV wiring

[winston1]

I've never come across anything that would combine the two sky feeds, and can't see how it could work.

It is called a stacker/destacker. It works by changing the frequencies of one feed to a lot higher and stacking them on top of the frequencies of the other. At the receiver they are destacked.
To work well it requires very high quality cable and careful attention to terminations, bends etc.

 

[Aragorn84]

how does that work with the LNB polarisation signal etc though? arent those supplied as "phantom power" back up the cable?

Google suggests the tuner applies 12-14v DC to set horizontal and 15-18v DC to set vertical

You cant apply two DC voltages to the same cable.

 

[ban-all-sheds]

Of course you can.


Just not simultaneously.

 

[EFLImpudence]

Why does Sky+ require two cables?

Why cannot one cable be used for the two tuners?

 

[Aragorn84]

because as mentioned above, the LNB requires a "polarity" to be set by the tuner.

If you joined both tuners to one cable, you'd end up with only one polarity available.

If you happened to tune into two channels which were on transponders with the same polarity, then it would work fine.

If you tried to tune into two channels which were on transponders with different polarities, it wouldnt work.

Read this:

http://www.satcure.co.uk/tech/lnb.htm#nosplit

 

[Aragorn84]

Of course you can.


Just not simultaneously.

I guess the stacker/destacker units could process the signal coming from the tuner, send them to the other unit encoded in some fashion and then make them reappear on the cables at the LNB end.

 

[winston1]

how does that work with the LNB polarisation signal etc though? arent those supplied as "phantom power" back up the cable?

Google suggests the tuner applies 12-14v DC to set horizontal and 15-18v DC to set vertical

You cant apply two DC voltages to the same cable.

Either you or Google have got the voltages the wrong way round.

Not sure how the two DC voltages are sent up the cable. Must be some form of coding on second one I presume.
http://www.satcure.co.uk/accs/stacker2.htm

 

[JohnW2]

Of course you can. Just not simultaneously.

That's true, but it could only work if there were some sort of chopping/time-sharing of the RF signals being received and processed, since the LNB presumably could not be functioning simultaneously with two different polarisations. If there were two LNBs, with a common multiplexed cable, that would be different.

Kind Regards, John

 

[Aragorn84]

how does that work with the LNB polarisation signal etc though? arent those supplied as "phantom power" back up the cable?

Google suggests the tuner applies 12-14v DC to set horizontal and 15-18v DC to set vertical

You cant apply two DC voltages to the same cable.

Either you or Google have got the voltages the wrong way round.

Not sure how the two DC voltages are sent up the cable. Must be some form of coding on second one I presume.
http://www.satcure.co.uk/accs/stacker2.htm[/QUOTE]

Yeh my mistake.

 

[eveares]

Ah, that explains it! Thanks. I must confess that I had assumed that Sky used a single frequency band with a single polarisation, thereby not needing anything like as 'clever' an LNB as you are describing.

You may find this interesting: http://www.lyngsat.com/packages/Sky-UK.html

Each channel requires the following parameters to be set up correctly in order to be picked up by the LNB. These parameters change with each channel and multiple channels are usually hosted together on the same parameters.

The parameters:

1) The frequency

2) Vertical or Horizontal polarization (V=13 volts /H=18 volts)

3) The Symbol rate

4) The forward error correction (FEC)

Thus by adding channels manually and setting the above parameters as so, you can sometimes find test patterns, streams and other non standard channels not included on the EPG amongst all the normal channels included on the EPG.

 

[ericmark]

I don't think it matters how it just is possible that's all we need to know but in the main shoot gun cable is used with two independent feeds only when hard to run another cable would the specials be used.

But the cost is so variable and so is the quality. So to finish watching a program in bed on a 10 inch TV RF is good enough but to watch on a 40 inch TV in kitchen RF is rather poor quality.

RF also has some odd things when I switch on main TV I can still watch Sky in dinning room but the signal from the SCART to RF which sends signal from Blueray player fails once main TV is switched on even though the sky box is always running.

However my bedroom TV works at all times.

This is the big problem until to try it you don't know if it will work or not. Even next doors TV can mess it up.