My Sky Digital is (still) broken!

There is a limit to the number of LNBs you can fit to a dish. Dishes are engineered to have a single 'focal point' (I don't think that's the correct terminology) - that is they reflect the signal back in only one direction so by definition only 1 LNB can receive a perfect signal from the dish. As soon as you add any more, the LNBs are offset from the focal point of the dish and therefore are receiving a weaker signal. If you add too many LNBs the signal on the outermost ones starts to degrade, very rapidly degrading to the point of non existance. At that point, you need to make the dish bigger so that all the LNBs can pick up a decent signal. But if you make the dish too big, you start to pick up more than one satellite at once, causing more interference.

Whilst I don't know what this limit is (and it can vary with quite a number of factors), there is a calculable limit to the number of LNBs (as in separate boxes) you can mount on one dish and in practice you would get nowhere near this as (for Sky Digital anyway) 4 outputs is the most you would need and you can buy a quad LNB.

The number of receivers you can hang off one LNB is determined by the number of outputs on it. Most LNBs have 1, 2 or 4 outputs.

Anyway, if you have a proper distribution system, you can mount a single Sky minidish with the quad LNB used in Sky + installations, and then attach as many receivers as the distribution system supports, which I'd imagine is exactly what is happening here.

UPDATE:

A few weeks ago, I called out a local satellite and aerial technician, who realigned the dish and managed
bring all the faulty channels back from digital oblivion. Unfortunately, about 2 weeks after the technician's
visit, the same problem had started to occur again, requiring another call out from the technician.

On checking the Services - Signal Test option on the Sky Guide, the Signal Strength was displaying at
about 30%, and the Signal Quality was displaying around less than 10%. The technician said that this
would be due to the age of the (first generation Amstrad DRX100) digibox that was installed, and that
it would perhaps be worth replacing this old Amstrad box with a newer more up to date digibox.

Today, I have acquired a Panasonic TU-DSB31 digibox. I've plugged it all in, inserted the viewing card,
and phoned Sky to get the box paired with the card. But, this was easier said than done, as it turns
out that the digibox system software is out of date, and incompatible with the viewing card.

So, I was advised to give the new digibox a forced software update, which meant removing the card.
unplugging the digibox from the mains power, hold the "backup" button on the front of the digibox,
plug it back into the mains and wait for the "Updating System Software" caption to appear.

I was advised by the Sky technical adviser to leave the box on standby for at least five minutes after
the software update, to allow the box "to settle". After a settlement period of around seven or eight
minutes, I went to put the card back in it's slot, and took the box out of standby mode.

The system software still appears to be an out of date version, there is still a caption saying "there is
a problem with the viewing card", and now ITV1, Channel 4 and five don't even show up on the EPG!

Since I'm determined not to have to pay £65 for a Sky technician to be called out, and since the work
the local satellite/aerial technician carried out (for £25) has a two year warranty, I've just phoned them
up again, and they'll be calling round my humble abode tomorrow afternoon to see what can be done.

If I need to call out a Sky technician to sort this out (for £65) it'll be strictly as a last resort only!

The terrestrial channels have vanished because the box thinks its in free-to-view mode, and will show all the sky channels, but will say, 'please insert viewing card' or 'problem with viewing card' or something to that effect. Sometimes you may even get 'no satelite signal being recieved'. Once you get the box and card sorted (which i suspect sounds like a problem sky's end), everything will come back, and you are sorted!

All they said at Sky, after the rigmarole of system checks and software updates, was that it would
require a call out from a Sky technician! (Which would be £65 I can't really afford at the moment!)

It did surprise me though, when the Sky customer adviser said to me "You're welcome to call out
an independent satellite engineer to have a look at the box, if you think that it would be cheaper."


(Having said that, If my Sky Digital equipment was still under warranty, I wonder if they'd
have the nerve to insist on having a Sky technician called out to get the problem sorted?)

In the early days of Sky Digital, somebody advised me to NEVER put the card in until the box actually ASKS for it.

I've followed that advice and never had any problems.

I'd therefore suggest switching off the box again, unplugging it for a couple of minutes and pulling the card out.

Then plug it in, wait thirty seconds or so and take it out of standby. Wait till a message ASKS for the card, then try putting it in.

Not saying that WILL work for definite, but it'll cost nothing to give it a try.

Thanks for that, but no, unfortunately it didn't work.

Meanwhile, signal strength and quality are showing up a little better on this new digibox. The signal strength
meter shows as around 70%, and the signal quality shows as about 20%. Some of the channels are still
breaking up a bit, so I think the dish may still be slightly mis-aligned. Thankfully, most of the channels
that are still not coming through properly are those p*ss poor lame ones between EPG# 200-301.

Also, the signals from the MTV/VH1 channels aren't coming through very well, nor is Sky News.

I'm always having problems with my box. Sometimes we cant get a lot of the channels, including ITV2, BBC One (although BBC One London is fine), e4, channel 4, Sky One...

Then it's back to normal, but not for very long. The signal strength always seems the same on mine, about 80%. Another thing bugging me is why by default on ITV1 I get Anglia West, I'm in Norwich, I should get East.

Although I have plenty of time to moan, I never get round to actually doing anything about it.

That's really not good. Signal quality is your main worry, that should be at least 60%. I think you've done the right thing in getting your engineer back out.

In theory you only need one dish with one Quad LNB to cover as many receivers as you like.

This is because an LNB only actually has 4 states (Lo-H, Lo-V, Hi-H and Hi-V) - so you can get all 4 options out of a single Quad LNB, and then feed these four outputs into a 4input, 20 output switch to feed each of the 20 receivers.

(At one point you could get different types of Quad LNB - one with four individually drivable outputs - suitable for Sky+ and Sky receivers, as you discuss. The others just had 4 outputs permanently in the 4 states mentioned above. However this isn't really needed as you can force a Sky style Quad LNB to do the same thing!)

ANOTHER UPDATE:

Just by chance, after watching the late night film that's just finished a short while ago on BBC ONE
(which had been defaulting to BBC ONE London all day) I started flicking through what channels I
could get, to see if there'd been any change regarding the poor signals I've been getting lately.

There was no change, but it was a long shot. Eitherway, I decided to try just removing the viewing
card, and putting the box into standby for about 15 seconds. Another long shot, but worth a try I
suppose. Or so I thought. I switched it out of standby, then put the viewing card back in when
it prompted me with the familiar "Insert your Sky viewing card" on screen caption.

It still said there was a problem with the card. That was until I switched to a random channel that
requires subscription authorisation from the card to unscramble the channel's encrypted signal.

That channel was PLUS. Lo and behold, the caption "Initializing new Sky viewing card" flashed
up on screen for barely three seconds, and PLUS was suddenly unencrypted. Hmmm, a bit of
a result I thought. I switched to ITV1, and that also appeared. So to did all the other channels
that I currently subscribe to. Trouble is though, I'm still suffering from bad signal problems.

Hopefully that should be fixed this afternoon when the technician comes back again, and I'll
be to enjoy my Sky Digital again albeit on a much, much faster, more up to date digibox!

Ah, well done.

That was the SORT of thing I was expecting it to do when I rambled on up above.

It obviously needed an extra prod, over and above what I suggested.

Local "aerial-repair-man", with shorts outside his overalls, ought to be able to fix the rest quite easily now.

Well, here's hoping . . .