Done a bit of browsing, seems that the signal can be confused with local analogue signals and give false readings and it's the quality that really needs to be high. Still confused a bit as one guy on a forum said that the quality needs to be 100% for most channels and he seemed to know his suff, but in the same thread another guy said his were 45% each and he had perfect pic/sound? lol
I think my problem was my amplifier amplifying noise and giving false signal strength. Still confusing why the quality should jump from 100% down to 40 back up to 85 and down to zero in a matter of seconds?