MM wrote:
Snip
Initially, I tried setting up the TV in the living room, the one place
where the picture was grainy on the analogue portable. The LCD TV said
"weak or no signal".

Which proves you have a cable related fault. Or, as an outside chance, a
fault on the distribution amplifier. But you've tried swapping the
connections round at the amplifier end?

So there's definitely a problem there. To cease with the guess-work I
have measured the actual length of the cable from the amplifier to the
wall plate: 13 metres +/- 20cm

The length to the kitchen wall plate is a lot shorter. I haven't
measured it, but it'll be about 6m

Which, with undamaged cable and a decent joint at each end will make sod
all difference. If one had been 50 metres and the other a couple of
metres, maybe you'd see a difference you could show with a meter.

--
Tciao for Now!

John.