Random loss of TV signal

[monday]

Many thanks for efforts so far - now an update. I have a 10dB attenuator in the coax aerial lead. Unfortunately, it has made no difference to the interruptions but the following data may be useful.
Before installing this, signal quality and strength data was:

TV Channels 01 to 40: quality consistent at 99-100/100, strength 90-93/100
EXCEPT Channel 08 which was quality 100/100, strength 55/100. This seems odd but is consistent with this channel commonly pixelating on my old non-digital set.
After installing the attenuator, signal quality and strength data is:

TV Channels 01 to 40: quality consistent at 99-100/100, strength 70-74/100, except Channel 8 quality 100/100, strength 26/100.

Assuming that the typical unattenuated signal strength of 70-74/100 is equivalent to rodders53’s calculated signal strength of 68dB, I can adjust that by proportion to (70/90) x 68 = 53dB – which puts me in the right signal strength range. Nonetheless, the problem continues. Interruptions are random wrt channel and timing. Further suggestions are welcome.

 

[Rodders53]

LCNs 1-40 are all SD DVB-T Channels.

LCN 1 (&2 and others) = BBC A mux f.ch 23
3 (&4,5 and others ) = D3&4 f.ch 26
40 is ArqA mux f.ch 22
39 is ArqB f.ch 28
38 is SDN f.ch 25

You've missed LCN 101 BBC ONE HD for the BBC B (HD) DVB-T2 mux on f.ch 30. But that may not matter in the grand scheme of things.

LCN 8 is Local TV - on frequency ch 35 and lower power (34kW cf 200kW). Transmit antennas lower on the tower and not omni-directional. Uses an 'easier to receive/more robust' QPSK transmit format so the lower power then just works.
See https://ukfree.tv/transmitters/tv/Crystal_Palace the red pattern.
Your location seems to be very much in the service area (98% of locations served) and max power I think.

Quality matters: A steady Q of 100 usually means all reception errors corrected and no picture sound interruptions. It matters not that the S drops from 55 to 26 if the Q stays steady at 100 for that particular frequency.

NB The TV meter is a random scale and differs from make to make an unlikely to be linear (or logarithmic). The 10dB attenuator will reduce the signal by 10 dB so if it was 68dB it would become 58dB... On your TV S90 -10dB = S70 and S55 -10dB =S26 as measured by you, above!

I'm now reasonably convinced its not overload or excessive signal based on your measurements. The attenuator is almost certainly not needed. It must be some other form of interference. The new amplifier has built-in 3G/4G mobile phone filtering but not 5G... Check if https://restoretv.uk/ has leafletted your locality and a mobile pole has appeared in your area - although I'd have expected such interference to be far less random and intermittent than you describe.

Which TV channels are affected by these random interruptions?
In your original post it was LCN 28 ITV Quiz on the D3&4 multiplex that you mentioned; so should have also affected ITV1 SD, C4 and C5 SD as well (among others on that frequency).

The trouble with random and very intermittent problems like this is tracing them / tracking down the source. It could be electrical interference from an unsuppressed, faulty, switch (fridge, freezer, heater, pump) in or outside the home. Switching on and/or off causing an interference spike either as a radio signal or conducted in via mains wiring. Faulty street lamps (discharge type) were a common issue once, largely gone with LED.

 

[accelerator]

If you've got fast broadband, you can buy an Amazon TV Stick and stream all the TV channels instead.

 

[monday]

rodders53, thanks for comprehensive reply as usual. I checked the restore TV site and no new masts etc. The ukfreetv/transmitter site led me in some interesting directions, including a BBC freeview site which enabled me to submit a request for an engineer visit with talk of possibly fitting a filter of some kind. Whether it will come to anything is another matter; your point about tracking down the source is well taken.

I have had a look for possible electrical appliance interference but at the time of night when this interference occurs (ie when the set is on for us to see it) there is really nothing running except the fridge and freezer. Neither of those is new by any means but could have something breaking down? - I might try turning them off for an evening to see what happens. A new EV charger was also a suspect but this interference is occurring before that starts up off peak at 2330.

Thanks again for your help, I'll update when I find a solution.

 

[Murdochcat]

We are in GU21 and never have issues with our terrestrial tv signal at all

 

[monday]

Neither did I until I got this expensive new Sony TV!

 

[Murdochcat]

I would return it

 

[monday]

Been through that stage! Sony's authorised repairers are sure it is a signal fault and I am inclined to believe them. Current investigation is focussing on a sensitive modern TV tuner trying to react to spurious signals from electric interference (where from is the problem?) or possible mobile phone network interference which it is not designed to deal with. Mobile network seems unlikely as there have been no local changes and no-one else in the neighbourhood seems to have a problem.

 

[monday]

An update and some success. BBC Reception Advice thought mobile network interference unlikely as no other complaints from my post code but suggested contacting Restore TV. Restore TV, on the basis of a questionnaire they sent me, thought it could be mobile network interference and sent me a filter. With that fitted, interruptions are much reduced but still the odd one. From another part of the Restore website, I can see that there are ongoing engineering works at Crystal Palace which may cause 'pixelation and flickering on some or all channels' so I need to wait for that to finish before I am certain. Restore TV say they are happy to think again if it hasn't fully worked.

Incidentally, Restore TV, responded to my query, sent me a questionnaire, responded to my answers and despatch a filter all within a working day. Great service. And thanks again to rodders53 for advice and very useful contacts.

 

[monday]

A further update. When the filter didn't work, Restore TV sent out a technician who quickly confirmed that mobile network interference was not the issue. However he kindly did some further testing and identified a 20dB signal drop between the splitter output and the wall socket in the TV room. He also pointed out what should have been obvious, that the aerial cable started off brown at the splitter and ended up white at the TV socket ie there was a join somewhere. That reminded me of an intermediate TV socket installed 20 years ago behind a bookcase which I removed but it made no difference. I have now abandoned that coax routing and run in new coax (about 9m) all the way from splitter to socket.

Signal quality is now 100/100 on all channels and strength 100/100 on all channels except Channel 8 where it is now 97/100. The Restore TV technician explained to me that the on screen diagnostics will still show high % signal and quality provided they are at a level within specification. Looking hopeful!

BUT I am still getting short blanks as before. Not as frequent eg last night just two about 10-20s apart. If it gets no worse, that is tolerable but I am determined to get to the bottom of it, frustrated that a new high quality TV performs worse than any of my others. Next stage is probably an aerial installer for testing and possibly a new aerial - the existing one is as old as the house which is 28 years - unless anybody has any other ideas? The only other thing I can think of is electrical interference; tonight I will switch out the fridge/freezer while we watch TV to see if that helps.

Thoughts welcome.

 

[securespark]

I know this might be a bit of expense.

But what about installing a separate, new high quality aerial (on a tall pole if there are nearby trees) and running an unbroken co-ax direct to the TV to see if bypassing all of the existing stuff makes any difference?

 

[Rodders53]

Back to first principles. Aerial direct to this new TV cable using a joiner.

Still doing it : trying some attenuation in bit by bit process of elimination of stuff... 4dB, 6 dB, 10 dB. If nothing fixes it that way then it's electrical interference most probably.

If it's random electrical interference from thermostat switches, dimmers, arc street lamps, farm electric fences, then they need tracing...
Alternatives might be local radio amateurs or illegal walkie talkie / CB radio users?
Or even mobile phone handsets.

 

[monday]

I know this might be a bit of expense.

But what about installing a separate, new high quality aerial (on a tall pole if there are nearby trees) and running an unbroken co-ax direct to the TV to see if bypassing all of the existing stuff makes any difference?

Thanks for that. I follow the logic but as you suggest, might be rather expensive! Probably similar cost to getting a tech out to fix it, with a new aerial if necessary. But see next reply.

 

[monday]

Back to first principles. Aerial direct to this new TV cable using a joiner.

Still doing it : trying some attenuation in bit by bit process of elimination of stuff... 4dB, 6 dB, 10 dB. If nothing fixes it that way then it's electrical interference most probably.

If it's random electrical interference from thermostat switches, dimmers, arc street lamps, farm electric fences, then they need tracing...
Alternatives might be local radio amateurs or illegal walkie talkie / CB radio users?
Or even mobile phone handsets.

Rodders53, thanks again. The interruptions are down to one/night, a pair of blips, 10-20s apart. The form of the interruption is so regular (only random factor is timing, anything from soon after switch on (around 10pm) to after midnight, that I feel it must be some form of electrical interference. Something that this TV tuner is sensitive to, that previous TV's were not. Definitely not streetlamps or electric fences, so left with dimmers or thermostats but really nothing operating at that time of night. I'll try putting some attenuation in and see if I can get a compromise signal strength.

Watch this space.

 

[Rodders53]

No point attenuating without eliminating that Distribution Amplifier and having a direct connection as it is mainly to check for possible signal overload (again).

On the other hand something so unpredictable and happening so infrequently may not be worth the effort of trying to trace it.

Poorly suppressed motor switching and thermostatic switching of heating elements are the commonest caused - either closing to make the circuit or opening to break. Also switches on lamps (esp. filament type) could arc/spark if operated slowly enough manually - better makes would snap open/closed to minimise any such. Outside PIR light switch operated by a fox, dog, cat or spider perhaps?

All depends on how much time and effort you wish to expend on finding it.