I have been having issues with pixelation on UHF. I checked the antenna and cables but couldn't find the problem. We are in a fringe area though reception used to be perfect. 

I decided to try an in-line masthead booster just to see if it would help. Rated frequency range is 47-862 mhz, gain 13-18 db. It seems to work fine with some channels, like Apnia and the Chinese ones, but not at all with TVNZ or Media works. If I put it in the cable those disappear completely. No signal at all. If I take it out they come back, but with pixelation. 

Can anyone shed light on this? I assume it is a frequency issue, but I don't understand why it is happening. I think the booster is probably working correctly. If I switch off power to it while it is in the cable, everything dies so it must be doing something. But no trace at all of TVNZ or Mediaworks, just all the other channels.