When we get Sky installed we read through the instructions (or we should anyway ;-) and one of the things that we notice is that bad weather can affect the picture quality. The guide mentions such things as heavy rain, snow, and high winds as likely to give trouble and cause "blockiness" or even no signals at certain times.
That's understandable but why do we get so many calls about poor pictures in late spring and early summer when there isn't a cloud in the sky and the temperature is in the '80's?
The answer? trees, leaves and water vapour!
When the Sky engineer installed your dish all those years ago he may have had to place it below eaves height, perhaps in the back garden, especially around here where so many homes are in an area of Outstanding Natural Beauty, or are in National Parks, or are on Listed Buildings. Here the installer tries to put the dish where it won't upset the local planners or the neighbours (who still in some cases think that Sky dishes "radiate death rays into space")! Often the best place is near ground level just above window height where tiny hands can't touch, but this problem can apply to ALL installations.
So when the dish was installed it had a clear line of sight path to the Astra satellite 28degrees East of South and (from the UK) about 30degrees up in the sky. Unfortunately trees, bushes, and even flowers grow, and grow. Eventually something will get between the dish and the sky and here the problems start.
Often, in the afternoon or evening the pictures on some channels will suddenly turn "blocky". The reason for this is often that the signals have suddenly reached a threshold where the receiver can't "work out" what it is seeing. This is a major problem with digital reception. The system chuggs along with the data being just good enough to give a satisfactory picture until a threshold is reached and the receiver suddenly just gives up. Notice certain channels will be affected while others seem perfect. So a common reaction is "All the pictures come from the same place so it CAN'T be Aunt Ethel's rose bush". Well unfortunately it CAN, and usually IS!
The reason being that while all the pictures come from the same point in the sky they do NOT all come from the same satellite and even then some are transmitted in one "waveband" and some in another, also some are "vertical" and some "horizontal". Just as some television aerials have their rods one way and osme others have them the other.
In many areas the BBC channels are the strongest while in other areas (really out of the intended range of services, such as Spain) the BBC are very much the weakest. this is because the BBC use a different satellite to many other channels.
All Sky receivers give a Signal Test where the receiver shows two bar graphs. One giving Signal Strength and the other Signal Quality. So which is the most important? Surprising ly it's the quality that is far more important. The receiver can compensate for low levels of signal by amplifying but as soon as the quality drops below a certain level then the poor old receiver just gives up!
So the cure is to chop the offending leaves off so that the quality rises again, and it can just be a few leaves that cause all the trouble, or if cutting will cause a family outcry the next time that Aunty visits at least tie the leaves well out of the way.
There is one other point that must be made and this is the hardest thing to explain unfortunately. The leaves do not have to be in direct line of sight between the dish and Sky satellite to cause trouble, as they (and this is especially true of trees) can disrupt the signals by the water vapour rising ABOVE the plant. This is quite enough to ruin reception, so you need clear air for several feet ABOVE the plant too.
Now do you understand why chopping a hole in the bush, which one person did, isn't good enough? ;-)