DVB-S dual tuner with splitter (1 Viewer)

[RobNorthcott]

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I'm sure I've seen this discussed before but I can't find it...

Thinking about the possibility of using a power-pass splitter to get some use out of a second DVB-S card without having to run a second cable to the dish. Seems tempting for the price of a splitter, but I can think of a few reasons why it might be too much hassle to be worth doing.

I've only got one cable to the dish, but there will shortly be a dual tuner in my HTPC. Running a second cable for a dual LNB would obviously be the best solution, but it's all the way through the house under the floor so it's not going to get done in the near future! On the other hand it would be nice to make use (even limited) of the second tuner...

Using a power-pass splitter would mean in theory the second tuner could pick up any transponder on the same polarity as the first tuner. Sounds useful, but would only be practical if MP's card selection code knows that the polarity has to match. Also I suppose it would have to know to leave the first tuner enabled to power the LNB in the case of overlapping recordings where the "slave" tuner's programme continues after the main one has finished.

Has anybody played with this sort of thing with any success or is it just a massive can of worms? (or should I just get my arse in gear and run that second cable? )

Rob

 

[jameson_uk]

The DVB-S feed bit would just about work but the main issue here is that there are very few channels on the same transponder.
This however is a mute point anyway as MP will open up the whole transponder on a single tuner anyway so you can do this on a single tuner.

There is absolutely no benefit in using a second tuner this way ( and there are many issues too but the above should be reason enough not to bother...)

The only way to make this work is a second feed to the LNB

 

[RobNorthcott]

I agree it's probably a can of worms. If it could be got to work though it would be better than a single tuner - with one tuner you can get all channels on one transponder, with two tuners you should be able to get any two transponders at once as long as they're on the same polarity (H/V). Or am I wrong about that?...

But I'll probably just put a second cable in sometime...

Rob

 

[jameson_uk]

I agree it's probably a can of worms. If it could be got to work though it would be better than a single tuner - with one tuner you can get all channels on one transponder, with two tuners you should be able to get any two transponders at once as long as they're on the same polarity (H/V). Or am I wrong about that?...

AIUI each LNB only has one polarity at a time so you can not pick up H/V from the same LNB

see Low noise block-downconverter - Wikipedia, the free encyclopedia
The combination of supply tone and voltage will determine both Hi/Lo band and polarity. You can not mix these

 

[RobNorthcott]

That't what I meant. With two tuners you could in theory pick up two transponders on one LNB as long as they are of the same polarity. (and in the same Hi/Lo band of course)

Sounds cool, but I think limited usefulness in practice (considering the cons) with the channels I usually have conflicts with.

Rob

 

[jameson_uk]

That't what I meant. With two tuners you could in theory pick up two transponders on one LNB as long as they are of the same polarity. (and in the same Hi/Lo band of course)

doh for some reason I was thinking you wanted to tune to x Khz V and H at the same time....

Once the LNB is pointing at the right band and polarity I guess you could tune to any transponder but MP would not cope with this very well. If you only ever watched one feed of live TV and had one recording it may work but then add in anything like EPG grabbing or multi-seat and it goes haywire. MP will always kick live TV in favour of recordings but if you have two tuners setup MP would assume they could both tune to all channels so a recording might start on card 2 but if you then turned on TV then card 1 would set the LNB for live TV and the recording would be messed up (or they would start fighting and nothing would work)

 

[RobNorthcott]

The more I think about it the more I think it's never worth bothering with just for the odd time when it may be useful - too many nasty side-effects. I'll just stick with using one of the tuners until I can be bothered to run another cable.

 

[Nil Einne]

This depends somewhat where you live. Here in NZ, all channels are basically on the same polarity (horizontal) and same satellite Optus D1 (the polarity of some was changed partially I think for this reason). Many have dual throat LNBs which can receive from another satellite Optus D3 but it can only receive one satellite at a time anyway and AFAIK nothing useful currently broadcast on it reaches NZ with 65cm satellite dish most people have. You can get a few Australian channels (SBS) via the vertical polarity on the main Optus D1 satellite but that's about the only thing which conflicts. Everything else is fine provided of course you make sure you provide power to the LNB. Admitedly there are only two transponders used by FTA TV anyway although it's quite common people would want both simultaneously (if they aren't using DVB-T) so it likely isn't an uncommon thing here. However our NDS encrypted subscription Sky TV is also the same so some people may want more then two feeds.

I believe the said Sky TV r who probably installed most of the small satellite dishes used to do the splitting thing for multi room and even their PVR (MySky) installs! Now they have bought capacity on Optus D3 there are constant rumours about what they're planning to use it for, some say possibly extra HD channels. So for new installs they're providing two feeds and a new quad LNB (which can theoretically receive both satellites and both polarities at the same time at a time although they only bother to provide two feeds I believe).

However the fact AFAIK many their PVR box installs still only have the dual throat with single feed suggests it may be a fairly long term plan http://www.geekzone.co.nz/forums.asp?forumid=106&topicid=73482 . (I wonder if they could dump some of the SD channels on it. This would make problems for those using a FTA box or computer config but they wouldn't care. However this would mean they need to enable HD reception/decoding for the channels which they dumped on the other satellite even without a HD ticket so PVR users could still record/watch these channels. They could potentially downscale internally if that's supported. Bigger problem is those with their older non HD PVR box. So all in all I'm guessing Sky TV is regretting their decision to be so cheap with installs but they rip us off so much they probably don't really care.)

The lack of any MediaPortal understanding of the concept does I think mean you will encounter problems if you try to record or watch SBS and some other channel but I think many kiwis with dual or more tuners get by with just a split signal.

Edit: Seems now there is also Nine, GEM and Go! from Australia although it's DVB-S2 http://www.freeviewshop.co.nz/channels-i-27.html

Edit2: Another likely problem if Sky TV ever do decide to use Optus D3 particularly for non PVR customers is they must still have a bunch of people with the older non dual throat LNB which can't receive it at all (well without realignment). They did make an effort to install the dual throats a while back, they came and replaced mine for example. Rumour had it the reason was they realised how SOL they would be if Optus B1 (at the time) ever died as it had had a temporary problem not long before. However I don't know how well this was completed, they allow you to move house without an installer if it already has a dish so some people probably had the old LNBs. I'm not even sure if they made sure they always replaced the LNB for when an installer did come out when there was already dish, e.g. for new installs to a house with an existing dish even if they did charge for it. I wonder how well even Sky knows what houses have the dual throat LNBs.