Originally Posted by spiney2:
“i fully accept what chris frost says. Knows his stuff. But recommended signal levels are very unrealistic. Leading to the OnDigital collapse, for example.”
Thanks. It's nice to receive an endorsement.
I'm vaguely aware of the circumstances of the collapse of OnDigital. You might have more knowledge on this than me. From what I gather some (most?) of the problems were financial (costs too high vs too few customers) as well as technical. Their service was collapsed about 7-8 years before the first phase of digital switch over (DSO). That's also well before my time in the aerial trade.
I don't know what the min/recommended/max signal levels were ON's DVB-T service. My guess would be that they were limited in transmission power at that time because the country was analogue. The threshold signals for analogue (pre- and during DSO) were much higher than digital. 60-80 dBuV was commonly quoted. I also know that transmitter power was upped for DVB-T as analogue was switched off. This caused a few problems for people with aerial amps set with gain to improve pre-DSO DVB-T reception.
The current recommended levels are correct for post-DSO UK. They should be achievable in a good proportion of the UK with or without amplification. There will be some exceptions though where local conditions make reception difficult.
Originally Posted by spiney2:
“if sig to noise dips sharply, intermittently, i don't see how any marginal improvement of 4 or 5 dB will help .... possibly think about a dish ?”
The problem for Alan_Paterson is that the signal drops both in Strength (and as a consequence in Quality too) at a very specific time of the day. So while it is intermittent it's also predictable. That's very unusual behaviour for a simple fault in some part of the reception system. Either the signal is bad all the time, or gets worse as some failing component degrades, or is intermittent and unpredictable.
In Alan's case it's almost as if the mast head PSU is on a timer switch. My gut reaction is that the system is picking up interference from some external source such as impulse noise from generators. This is getting in to the system via some poorly shielded part.
I also considered sun angle, temperature variation, Ham radio interference and a few other more obscure causes. But the time of year, weather variations and the reliable times when the issue starts and stops doesn't fit.
Right now then the goal is to make sure the system has good screening from external interference sources. In the absence of any new information then the only other thing that I can think of is that the Humax and TV signal meters are both very optimistic and the signal is much closer to 45dB strength than we are expecting. That would make it vulnerable to impulse noise. The question is, where from?