Hello again. I've been back at my flat for a few days and have found the problem's not resolved. But from what I've seen this week it seems that most channels are fine (have strength around 94 quality of 100 yet work perfectly), it's 3 specific channels which are sometimes on strength 18-22 and quality 100 and pixelate a lot or are on strength 0 quality 0 and show a bit error rate at the max and of course don't work at all at those times.
I've chatted to the neighbours at the other end of the aerial feed i.e. ground floor and they can't get those same three channels at all. Is there anything in that which suggests a specific problem to you?
I am really grateful for your help.
There are several things going on, but we still haven't got the whole picture from you to enable anything more than best estimate. Anyway, based on what info we have so far...
Your neighbours below don't get these channels because the signal loses some strength due to the resistance of the cable in the drop from your flat to theirs. The signal is too weak for these channels by the time it reaches them. They get the good channels, and at sufficient strength that they think it's all okay.
Depending on your local transmitter, it could be that the channels you're struggling to receive are at frequencies where your current aerial just isn't that good at receiving them, or they could be broadcast on a lower power, or they're at a marginal range. It could also be that the loft install is responsible for 'lumpy' reception... Or maybe even a combination of all of these factors!
If I was facing this as a call from a property owner, and given the limit that rewiring to the individual flats isn't available as a possibility, then I'd look at two options:
The quick and cheap solution is to kill the troublesome channels by introducing an attenuator. None of the TVs would then see the transmissions. A 6dB attenuator would probably do the trick. It's then just a question of retuning the top floor flat TV to exclude the channel allocations.
The alternative is to look at the whole system (including measuring all the channel mux strengths) to see whether it's possible to receive these channels. If so, then to overhaul the entire installation. This includes looking at the matching of the aerial to the local transmitter and possibly changing the aerial to a better new fit. Then mapping the loft to get the best aerial location if an outdoor fit isn't a possibility. Finally, installing a launch amp and tap system so that all the flats get the same signal.
That's about as far as it's possible to get without knowing which is the local transmitter and the UHF Channel numbers of the various muxes, particularly the troublesome mux.
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