inconsistent HD reception

My HD channels intermittently break up. They show blocking etc. This will go on for some days (it's happening now). Then they will become OK again for weeks. It's a single aeriel connected via HDMI. Standard def is excellent. So is HD usually. When it's breaking up, the strength is 45% (quality 100%). Very grateful for any advice.


Sometimes (?) the HD mux (transmitter channel) has a lower power than SD channels (that's a simplistic explanation). DO a Google to find WOLFBANE website and enter your postcode - it will give you what's available in your area.