Check Your TV Cables
So often I get called to fix someone’s television reception where the only thing wrong is the TV coax lead.
So, a really good place to start trying to help fix your TV reception yourself and save yourself a call out fee is to get a set of good quality coaxial television leads. The main TV lead has male PAL connectors on both ends.

Maybe you just purchased a cheapie one? Perhaps half the time it will be fine but if you connect it and you still have a problem you will assume the TV lead to be fine as its new and therefore the problem may be the antenna.
Better to use a good quality TV lead and reduce the chances of paying a call out just to replace the faulty one.