Dual LNB power supply?

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My sister-in-law has a shared comunal dish, and dual LNB, with a neighbour. It seems that if the neigbour turns off their decoder then my sister-in-laws TV goes off as well, except for Sky News (???). I understand that there is a seperate feed to each decoder from the dual LNB and there is no pass through from one decoder to another.

I am aware that the decoder provides power to the LNB and initially my thought was that this was the issue but then she mentioned the Sky News quirk.

With a dual LNB is the power supplied by ONE of the decoders or does each decoder provide power to its own part of the LNB? (I do not know which LNB they have in the system so if the answer to the power is not generic I will have to check it; roof of an 8 storey block of appartments)
 

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I can think of no reason why that would happen, aside from having a faulty twin LNB.
 
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My first assumption was that it was faulty but when the neighbours decoder is on then there is no problem with reception. I believe also that Sky News is a very strong signal and therefore it would account for only that being recieved when the neighbours unit is off.

Do you know if the two halves of the LNB are powered seperately? Instead of the LNB being faulty it could be that the my sister-in-laws decoder is faulty and not providing any DC power.
 

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steve.robocop.barry said:
Do you know if the two halves of the LNB are powered seperately? Instead of the LNB being faulty it could be that the my sister-in-laws decoder is faulty and not providing any DC power.
If a receiver is not supplying power to the LNB it won't be able to control the H/V polarity switching so quite a few channels would be missing if that was the case.
 

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Yes, each Port is powered separately via the coax connected to it: That cable carries power to the LNB Port, H/V and Band switching signals and the downshifted signal from that Port.

It's pretty clear that either the LNB is faulty, as what happens (or not) on one Port should not affect other Ports, or that your sister's Receiver is not providing the right outputs to the associated LNB Port.
 

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If your sister's receiver wasn't providing any power from the output, it would not be able to switch from vertical to horizontal, so a lot of channels would be missing, even when the LNB is powered by the other receiver. Sky news is on a vertical frequency in high band and she should also be able to get other channels if she can see that.

what receivers are they using?
 

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I would hazard a guess it is one of those really cheap passive distribution units, ie. no external power supply. They rely on the receivers own LNB voltage to power both the switch and the LNB.

YOu could probably check by making a call to the landlord for the specifications, or looking in the riser cupboards for something abut four inches square in size with about 12 connectors/cables coming off it, but no additional wire or transformer plugged into an electrikery socket.
 
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