Over the Christmas period I noticed that only on the BBC TV channels was there a break up of the signal which lead to little blocks appearing on the screen. I thought it could be the aerial which may need replacing or adjusting but all the other channels were fine.
Slightly different fault but possibly the same reason. I have a new TV and have managed to get all channels except ITV HD. A relation in the trade checked my system and suggested I changed the cable. He explained earlier cable had a plastic insulator between the inner and outer wire but had holes running through it. The latest cable has a solid insulator and therefore increases the strength of transmitting the signal. I'm off out to buy cable today, will report back if any difference noticed.
Vulcan. To clarify, the newer cable you describe merely has a lower loss (of signal) per metre. All cable gradually loses signal down the length; no cable increases the signal.
General point, signal strength received at the aerial can vary up or down due to (amongst many reasons):
Temporary signal reduction at transmitter when maintenance
Atmospheric pressure from weather
Rain in vegetation (trees) close to line of sight of aerial.