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Signal strength is not so important with digital TV as it was with analogue. Analogue needs a 30db S/N ratio to get a reasonable signal but theoretically a digital signal can be detected with a negative S/N ratio or a signal that is below the noise threshold using a computer process.
However to transmit a digitised TV picture requires a very high level of compression to keep it in the allocated bandwidth and this is where the problem lies. Simplified it means if one bit of information is damaged by some sort of interference the whole "frame" will not decode correctly. I expect some form of Hamming code is used to detect the integrity of the frame and if it fails the whole frame will be dropped. The loss of one frame will probably not be noticed but if the interference is severe enough to damage a high proportion of frames the picture will break up. I am not up to scratch in the digital TV as I have not been involved in TV for 30 years so my knowledge of digital TV is very basic.
Barry
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