I have picture breakup, specifically on BBC 1 SD, and BBC News but a few others. The signal strength is always around 90-100% but the signal quality is at 90% and then drops in fits and starts to 80, 60, 40 or even 0%. It can flit about between 40 and 90 in a second.
Other freeview receivers don't have any issues - I have an external aerial and no amps. The cables are in good nick. I have a 3G SureSignal box but the issue continues when it is off. 4G reception is marginal in my area. I have returned the TV channels
I wonder if the YouView box is getting co-channel interference and requires a Band Pass Filter. I am on the Hannington Transmitter in Basingstoke.. I think that is Group B.
I don't have an attenuator to hand... although I could put in some duff cable inline! If it was overloading, is that likely to affect certain channels whilst others are stable and fine?
Yes it can affect certain channels, depending on the mux signal level.
If you read the link I posted, you will see some other forum threads about this issue.
100% can mean over 100%.
What signal quality/strength do you get on other devices?
With NextGen (tiles) the calculation of signal strength changed to something less than helpful.
With the old calculation (the lists version) if you had a strength of 90% or higher you'd probably want to put an attenuator in line to reduce it to somewhere in the 70-80% range but NextGen ramped up the figures so on my boxes running OldGen (lists) I get a strength reading of 64% approx but on Nextgen that reading is 92% approx.
You've nothing to lose by trying an attenuator.