It is a feature of television signals that they can be effected by the weather. Aside from the obvious damaged that can be caused by wind or torrential rain, the onset of summer can cause a more intriguing problem called "inversion".
Basically, when the sun heats up the land, the hot air can get trapped below cold air at high level. This creates an "inversion layer" which acts like a polished mirror to TV signals. This causes two problems: you can receive both the original and a reflected signal from your own transmitter (on analogue TV this appears as "ghosting") or interference from TV transmitters that are normally too far distant.
The ITV/C4 multiplex of channels (ITV-1, ITV-2, ITV-3, ITV-4, CITV, C4, More4, E4, Quizcall) use a transmission "mode" called 64QAM, and it is sadly much more prone to these problems.
So, whilst a loft-mounted aerial will provide reception at some time, it will fail at others. The only real solution is to mount the aerial (or a new Class I aerial) outside on a pole, but some people report that changing the cable from the aerial to the set-top box to the high-grade satellite cable can also help.
The SCART connection, by the way, only carries a single TV picture, not the Freeview transmission multiplexes, so if this is disconnected it will result in degradation to every channel at once.
Karen McIntyre: Although in areas such as yours the Freesat route is indeed the best way to go, as reliable reception is virtually guaranteed using this mode, heavy thundery type downpours or snow on the bowl of the dish being about the only things that can affect it, although only for a one or two minutes or so in the case of a downpour. But though purely out of curiosity, on the occasions where your reception has gone downhill, are you aware as to whether or not your neighbours are also experiencing similar difficulties with their reception?
Margaret: Advice as to the possible reason for your problem can only be given once the following points are known.
(1) : Your location, this preferably being in the form of a post code or one from somewhere nearby, e.g: a shop / post office. This info being necessary in order to access information on the transmitter covering your area.
(2) : Do you have your own aerial? or are you connected into a communal system? such as used in apartment blocks etc.
(3) : Is the aerial connected directly into the TV? or does it pass through some other device first?
The aerial is digital and is in my loft, there is another television also connected to that aerial in separate room, that gets all the 80 stations. they both connect directly to the television, both tvs have built in freeview. I am near ka24 4jg
margaret: The Dalry area is indicated as being served by either the Darvell or Blackhill transmitters, the latter providing a better signal as far as the commercial channels are concerned.
However, as the TV in the second room would apparently receive all the channels OK, this then indicates that the signal is actually there, but is possibly being received at a level under that necessary to resolve a picture on your main TV, as tuner sensitivities vary from set to set.
Therefore, if your main TV is not wall mounted? you should try temporarily connecting it into the outlet socket used by the TV in the other room followed by carrying out a retune, if this results in the restoration of all channels? then the next stage is to reinstall the TV into its original location followed by checking that the channels normally viewed are still there.
Should they be OK? then this is inclined to suggest that your system could benefit from the addition of a powered amplifier / splitter to feed a higher level of signal into your two aerial outlet points.
However, before carrying out any of the aforementioned procedures, you should try carrying out a manufacturers reset on your TV or box, this procedure also known as "default setting" or "first time installation".