There are a number of things that can affect TV and radio reception. I expect that the current problems being described are due to tropospheric inversion. This is where the normal temperature distribution in the troposphere is inverted causing a change in the refractive index, which in turn causes electromagnetic radiation (i.e. radio waves) to “bend”. This in turn means that some waves that would have normally disappeared in to space come back to earth and interfere with locally generated signals. This link:
This will affect all signals to a greater or lesser extent.
If you watch analogue TV, you will occasionally see a “ghost” image which gets more noticeable as the condition worsens. As humans, we are very good at filtering out extraneous signals and we “lock” on to the image we want (although, obviously, if the effect gets bad, we will whinge about the bad picture).
Digital tellys are a bit different. They will also pick up the interfering signal, but their electronics does the filtering for us. So the picture will still look perfect even though there is a ghost/interfering image present. But, as the strength of the interference grows, the electronics will suddenly not be able to cope. This will then mean a block of data will be lost and an area of picture will pixelate. The stronger the interference the more pixilation until you end up with a few lost frames and the warning “Bad signal”.
Confusingly, therefore, for a digital telly, not only do you need a signal strong enough to detect, you also need good “quality”. It is possible to have two strong signals together that will lose you the picture, but one weak one which will be fine.
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