Well you've not got a switching problem since you have both high & low, V & H channels. I have checked those on my receiver and get similar variations in quality. However I am using a dedicated satellite box (a Technomate TM 1500) and a motorised 80cm dish. This has a more accurate and quicker responding signal & quality display than the typical domestic boxes. My parents used to have similar picture break up with their Sky system despite it showing good signal readings. I connected my box to the minidish and found by a careful bit of "tweaking" of dish aim that I got a noticeable improvement in quality, and they've not had any problems since. The best way to do this is with a professional meter, but they are £200 or so! If you want to have a play there are a couple of things to try.
1/ Replace the LNB - If it's the standard "clip in" Sky one you will need to either use the same type, or get a conversion kit from Maplin and fit a standard "Universal" LNB. Chose a low noise figure, they are only slightly more expensive but will help to make the best of your signal.
P.S. These can be moved in & out and also rotated in the clamp - you will need to "skew" (rotate) it anticlockwise looking from behind 5-10 degrees or so, and also experiment with the position since this is like focusing a torch to get the best beam.
2/ Try adjusting the dish aim. This is obviously a bit tricky with out the proper kit, but the normal DIY method is to rig up a TV where you can see it from the dish (upstairs bedroom perhaps?) and also have the signal display showing. The alternative is to have someone shout to you, but that introduces a delay! I would carefully mark the bracket to dish joints with a marker pen so you know where it is at the moment. Then loosen the clamp and rotate the dish slightly to left & right to see if there's any improvement. Wait for a few seconds each time for the readings to stabilise. Obviously aim for the best result, although the quality reading is far more important with digital systems. Then also try the vertical aim - this tends to be more critical. A good tip when doing this is to chose a weak signal rather than a good one since any failings will show up much quicker.
I trust you realise that the dish is actually "looking" up from where it seems to be pointing - most small domestic dishes are "offset feed" types rather than prime focus such as the huge uplink site antennas. The Astra 2A,B,C,D & Eurobird 1 satellites at 28.2 degrees East are at an elevation of about 25 degrees above the horizontal in the SE of England.
Looking out the window, today is probably not the best time to be climbing a ladder, so I will wait to hear what you've decided to do.
Last edited by The Flying Pram; 8th November 2008 at 11:05.
Reason: Addition of P.S.