Using a splitter to send signal to two boxes?

quenching

Just wondering what the situation is with putting a splitter on the cable coming from the dish to the digibox? I have a second digibox that I can get a free-to-air card for that I'd like to use in a different room, but when I put a 1 to 4 non-powered splitter on the input cable I get the "no signal being received" message on the current subscription box, do I need an amplifed splitter?

Am I doing something wrong here, isn't it just a straight forward coax signal to be split ?

Many thanks.

ShaneOC

It is not advisable (maybe not even possible) to do what you are saying. The digibox uses the cable to power the LNB so by splitting it you loose the return power path.

If you ensure that the power can get back to the LNB then having two boxes trying to power it could cause damage.

The best thing to do in your case is to get a twin (or quad) LNB. This is basically two (or four) LNBs in one. You can put these on the end of your dish instead of the single LNB and away you go.

spuddy

As far as I know you cannot so this - the only solution is to buy a dual or qual lnb (this allows multiple satellite feeds from the one dish) Make sure the lnb is designed to work on an ellipitical/mini dish. Run a separate cable (make sure it is CT100 grade not standard co-ax) from this to your other digibox. It is not difficult to do. If you have any other queries please private message me.

lawhec

This has already been covered...

http://www.boards.ie/vbulletin/showthread.php?s=&threadid=55284

Stiabhna

Quenching,

It does work - I have one coax cable coming out of the wall and have attached it to a non-amplified splitter, to which I have attached 2 sky boxes - 1 sub and 1 FTA.

The only problem I have is with UTV and the Scottish ITV stations, but this could be because I am outside the footprint (in Germany).

S.

ShaneOC

Originally posted by Stiabhna
Quenching,

It does work - I have one coax cable coming out of the wall and have attached it to a non-amplified splitter, to which I have attached 2 sky boxes - 1 sub and 1 FTA.

The only problem I have is with UTV and the Scottish ITV stations, but this could be because I am outside the footprint (in Germany).

S.

Hi Stiabhna,

I think that the problem you are having with UTV and the scottish regions of ITV is due to the fact that they are on verticle polarity (10.906V) whereas most of the other channels on Sky are horizontal (including the other two ITV frequencies). This coupled with the fact that you are on the edge of the footprint probably explains it.

Do you have any other problems with channels on verticle frequencies (most of the UK channels, UK Gold, UK Gold 2, etc)?

There is also some switching between high and low frequencies but I am not sure exactly how this works.

sirlinux

Just thinking could it be possible to feed the output from v and h onto the one cable coming from a dual lnb, obviously you would have to fit a filter to stop more then one box trying to feed dc down the line, and also find a way to lock one output of the dual lnb to v and the other to h

lawhec

It's not only the Horizontal and Vertical voltage switching that needs to be considered but also the 22KHz tone switching as well - there are four different states that a modern LNB can be in - low band vertical polarity, low band horizontal polarity, high band vertical polarity, high band horizontal polarity.

The Sky Digibox (in common with all satellite receivers) sends a DC voltage and a 22KHz signal (either on or off) to the LNB. The voltage determines polarity, the 22KHz tone determines the local oscialltor frequency the LNB uses. To determine the polarity a single LNB uses, the receiver either sends a 13 or 18 volt DC signal to the LNB. If it's 13V the LNB switches to Vertical polarity, 18V is Horizontal polarity.The osciallator is used to allow the LNB to shift the received frequencies from a satellite to a part of the spectrum just above the UHF TV band so that it can be sent down a cable to the Sky Digibox. Without the osciallator the 11/12 GHz frequencies wouldn't last more than a few metres down Coax-cable. The two oscillators in the LNB are fixed at (I think these are right) 9.75 & 10.75 GHz. The received signal is "mixed" with the osciallator (in a similar fashion to osciallators in TV & Radio tuners except LNB oscillators are fixed frequency) and the frequency difference between the oscillator and the satellite signal is sent down the co-ax cable to the satellite receiver.

As an example take Network 2 whose details are below...
Frequency: 10.744 GHz
Polarity: Vertical
Symbol rate: 22000
FEC: 5/6

The symbol rate and FEC are not important here are these are dealt by the reciever. What is important is the frequency and polarity. The frequency is in the "low band" so the 22KHz tone sent by the Sky Digibox is turned off and as the incoming signal is vertically polarised the Sky Digibox should send a 13 volt DC voltage to the LNB. In turn the LNB is switched to receive Vertically polarised signals and reject Horizontal signals, and the absence of the 22KHz tone means that the osciallator selected is 9.75 GHZ. Now for a bit of mathematics...

Frequency of received signal - LNB Oscillator Frequency = Frequency sent from LNB down Coax to Sky Digibox (all calculations in GHz)

10.744 - 9.750 = 0.994GHz or 994 MHz

Therefore the LNB converts to received signal to a frequency which can be sent down the coax to the Sky Digibox without serious losses. In fact it is not just Network 2 which is sent down the coaxial cable, so is all the other channels on that transponder and in fact all channels that are on transponders in the low band and are vertically polarised. The highest one of these is one which gobarkingmad is on. This is on one of the Eurobird transponders, 11.681GHz Vertical. Therefore while you are watching Network 2 on you Digibox, the signal which has gobarkingmad is also there on a different frequency. Working it out...

11.681 - 9.750 = 1.931 GHz or 1931 MHz. Therefore the tuner on the Digibox, having sent out it's instructions to the LNB on which band/oscillator and polarity to use, receives a wide range of signals over 937MHz approx., tunes into the one it wishes to use and then takes the stream of digital information it wants, in this case that for Network 2. If someone was then to switch over directly to gobarkingmad the oscillator and polarity settings would remain the same, it's just that the tuner would tune itself to the required channel. This is the same principle as a normal TV tuner (for this sake, one on UHF only) which has a fixed aerial receiving four channels and the TV tunes into one channel in the UHF band.

If this is what you wanted then yes, you could split the LNB cable to connect to two Digiboxes as both channels lie in the same band and the same polarity.

However say someone had the cable split and wanted to watch BBC1 Northern Ireland instead of gobarkingmad. BBC1 NI is on the following transponder...
Frequency: 11.720 GHz
Polarity: Horizontal
Symbol rate: 27500
FEC: 2/3

As mentioned before the symbol rate and FEC, although different to Network 2, is not important as the LNB doesn't handle this. However BBC1NI is on the lowest frequency of the "high band" and is also a different polarity - Horizontal rather than vertical. In a normal case the Sky Digibox would switch the 22KHz tone on to the LNB to tell it to use the 10.75 GHz oscillator and also send 18V DC to tell the LNB to switch the polarity to Horizontal. Now the cable has been passively split to feed two digiboxes, one on Network 2 and the other has just selected BBC1 NI - because the box which wants BBC1NI has sent the 22KHz tone the LNB switches oscillator and Network 2 is lost because it's signal down the coax is too low for the Digibox to tune into. Also because the polarity is set different for each box, the LNB cannot tell which polarity to use. It may by default go on to the higher voltage hence stay on BBC1NI but you will have lost Network 2, or that nothing will happen for either box. It might also be possible for the LNB to get damaged, dunno about the receivers themselves.

Therefore it is impossible for a passive splitter to feed two digiboxes with one wanting Network 2 and the other BBC1 NI. In fact Sky + has two tuners and needs two feeds into it, hence two leads from it's quad LNB. Also as well a passive splitter will reduce your signal to each digibox by at least 3db - if you live in a fringe area it will be a problem, and the signal will be more likely to go in wet weather.

Don't bother messing with a splitter as you'll end up pulling your hair out - get a quad or dual output LNB (Duals aren't available for the Minidish but are for "normal" dishes) and run a second line from the dish to the second receiver. A bit more expensive than a passive spiltter but you'll have no loss of signal for either box as each output acts like a single true output and have the full amount of channels available for both boxes.

It does work - I have one coax cable coming out of the wall and have attached it to a non-amplified splitter, to which I have attached 2 sky boxes - 1 sub and 1 FTA.

The only problem I have is with UTV and the Scottish ITV stations, but this could be because I am outside the footprint (in Germany).

If you can receive the other ITV stations then it aint footprint problems - the Carlton & Granada owned stations are on low band horizontal while the Scottish and UTV stations are on low band vertical. It would really depend what two channels are on the different boxes

Just thinking could it be possible to feed the output from v and h onto the one cable coming from a dual lnb, obviously you would have to fit a filter to stop more then one box trying to feed dc down the line, and also find a way to lock one output of the dual lnb to v and the other to h

Using a combiner is not an option because if the H & V signals were combined together there would be too much interference between conflicting signals for the tuner in the Digibox to allow it to tell the difference between a wanted and unwanted signal (A bit like adjacent channel interference with terrestial TV) besides the reasons why two polairties are used is to maximise frequency re-use. Anyway I don't think it could be possible - you're probably thinking of something similar to a combiner that allows the output from a VHF & UHF aerial to be connected to one downlead. The thing is there that the two aerials are meant to work in two different parts of the spectrum and the combiner isolates different frequencies for each signal which would say stop the VHF signal picking up a UHF signal and spoling the picture on a UHF channel. Even when using different oscillators it it still the same frequency range that the LNB sends out down the cable to the Digibox, in the range of 950 - 2150 MHz so having low band and high band channels down the same cable at the same time isn't possible.

Some people might wonder why there are "low bands" and "High bands" - well up until a few years ago the likes of Astra and most broadcasts from Eutelsat were in the "low band" but space was running out and new space had to be created. At first Astra 1D used frequencies below what was originally used which meant that many old analogue recievers could receive these channels unless they had the very common Global ADX which shifted these channels up to a frequency that could be tuned into by old receivers. Then when 1E was launched it was the first Astra Satellite to use the "High band" which was previously only used for the then high powered satellites like Marco Polo by BSkyB and the France Telecom satellites in the very high part of the "High Band". The problem was that with an LNB with a single oscillator could sent these "High Band" signals down the cable to the satellite receiver, these frequencies would be rather high that they would antennuate much quicker than those in the "Low Band". Also a tuner to cover a very wide spectrum would be very expensive to produce. Therefore the 22KHz tone was invented so that the "High Band" signals used an oscillator that converted these signals to the same that the "Low Band" used. Also it was backwards compatible with old LNB's as they just ignored any 22KHz tone that was ever sent.

TVDX

Just to let you know i recently tried this,
but i must admit, i only did it because i knew, i was getting a dual output lnb within a week or two, and it really is only a temporary solution.

You must intend on getting the dual output lnb or it will just mess up the one you already have by all the switching it has to do.

The handy way of doing it is get a list of the Sky digital channel frequencies and look for the V or H denoting the polarity, you know that if they are the same those 2 channels can be watched on seperate boxes, but the sad thing is the obvious combinations of channels you think you will get wont happen, for example Irish E4 is on a different polarisation then Channel 4 on your Free to Air box, so you have to switch to other channels and go the english E4. Its just a load of hassle and the last thing you want to be doing is cutting off the signal to your free to air card by switching on sub box to a channel of different polarisation, as you will then block the signal coming to free to air box and it may not get an update and could die.

I was very, very pleased with the dual output lnb and am now secure in the knowledge that both boxes are active and getting the satellite signal.

Genghis

Very informative post, Northern Correspondant - thanks!

Tony

Originally posted by Genghis
Very informative post, Northern Correspondant - thanks!

Agreed, well done Sir.

Tony

Michael Collins

Originally posted by Genghis
Very informative post, Northern Correspondant - thanks!

Post? That's a masterpiece of an essay...

Thanks too btw :-)

sergeant121

It was an extract from a book I use as a doorstop - War & Peace it's called!