Random loss of TV signal

[monday]

I had a new Sony Bravia 8 TV earlier this year. It replaced an older Samsung non-digital set. From the start I was getting short duration (1-2s) loss of vision and sound, random with regard to timing and channel, normally twice in a short interval, then maybe again an hour or so later. Not more than a couple of times in a night’s viewing typically 2200 to 0030. This was on terrestrial TV via conventional aerial, not router. VIdeo of this event finally captured and sent to Sony’s appointed engineers who changed the motherboard to no effect.

They then suggested it was a signal fault which I am inclined to agree with because of the random nature. I brought in a local aerial engineer who diagnosed low signal quality on physical channel 28, affecting all tv channels received through it. Signal quality was dropping to around 50/100, signal strength remained 90/100. Aerial here is tuned to Crystal Palace, we are probably 30 miles away. This was isolated to the coax connection between the wall socket and the TV. He replaced this ready made cable with a heavier coax cable with old fashioned aluminium plugs; problem solved and we both congratulated ourselves. Signal quality on all channels is now 100/100 except (clearly) when it drops out but I can only measure strength/quality on the TV itself, so can never catch it when it drops out.

Except it has started doing it again, not quite so often and on stations other than physical channel 28. The TV is fed from a powered 8 way splitter in the roof, cabled to a conventional roof aerial. The splitter feeds several other TV’s, including another Sony digital one next door, a few years older and some non-digital ones which we hardly ever use. The Samsung non-digital TV which used to be on this same coax lead never had any such problem although there was some pixelation on one or two channels, mainly TV channel #8 I think. The other Sony digital TV in the next room, on a separate coax to the same splitter also has no issues.

So, apologies for the length of this story, but any ideas? I am now sure it is a signal issue but from what source? It is easy to suspect the cabling from the roof splitter to the wall socket but why doesn’t this affect other TVs, or the old TV when it was in the same room. Could there be local drops in signal quality from the transmitter due to atmospherics? - but this has been ongoing from February to June. Local interference: switching, microwaves, WHY.

Grateful for your thoughts.

 

[Rodders53]

Location? Where are you relative to CP? (Nearby postcode ideally within 100m, but place name will suffice.)
What aerial do you have? Where (loft, roof, room)
Any amplification (signal boosters).

The symptom (High signal with quality dropping causing glitching) can be due to too much signal, so overloading the TV tuner. A signal reducing attenuator should fix if that's the cause.

Welcome to BBC Reception Advice | Help receiving TV and radio

www.bbc.co.uk

Current (still) high pressure may mean co-channel interference giving the same symptom... Check if your reception prediction suggests that is likely https://www.freeview.co.uk/corporate/detailed-transmitter-information
If so 'do not adjust your set' is best advice. We've had some HP weather systems this year which may have coincided with your issues?

 

[monday]

Thanks for quick response.
GU21 area, google puts me 33 miles south west of Crystal Palace.
Conventional aerial, roof/chimney mounted on 2-storey house, been up there 28 years.
Powered splitter in roof space, 8-way Maxview with slide in plugs (ie not F-type). I actually changed this as part of looking for a solution,
Previous one would also have been 28 years old, 3-way, powered but thought it might too many Y-splitters on it so changed it. No difference.

I had a look at the BBC Reception site. Aerial engineer was clear I was tuned to Crystal Palace. It noted some atmospheric (high pressure) disturbance from 23 June but as above this has been going on since February. I’d seen the detailed transmission site from another thread but had another look. Signal strength on all Freeview channels was good. My aerial engineer seemed to attribute more importance to signal quality than strength but both were good.

I hadn’t thought about too much signal! I’ll look into the attenuator. I did wonder if the latest TV’ were more sensitive to signal and perhaps blanked the picture rather than pixelate. Our only other digital TV, also SONY, is several years old.

Thanks for your help.

 

[monday]

Thanks for this. I noted your comment about sensitivity of some Sony TVs and that had been my suspicion as well. I will try an attenuator - surprised to find how cheap they were (about £5). Presumably I could fit this directly in the coax line to this specific TV? I could put it upstream of the splitter but getting there involves some acrobatics because our builder gave us a nice clear roof space, then put the cold water tank in the way! I’ll try a reset as well - I can do that just by turning off the upstairs lighting circuit that it is wired from.
Thanks for your time.

 

[ericmark]

Could be Isotropic propagation. If cold and hot air hit each other, it can form a reflective layer, if that layer is above the transmitter and receivers aerials it can allow huge distances to be covered, but if one is above the layer it can also stop the signal, if you note in Autumn smoke going up so far then spreading out, the point where it spreads out is the layer.

 

[monday]

Thanks. Valid point but this has been going on for months. I don't think the atmosphere is that consistent!

 

[evdamadiynot]

Recently had major trouble with intermittent tv signal
obviously did a rescan first then
Started at the top with checking ariel orietation,then the booster which I bypassed and tried a new cable
All to no avail.
Tried a different tv set which made no difference.
Just before buying a new fly lead I cleaned up the old one with some wire wool
Full signal restored.
Worth a try

 

[Rodders53]

Are all the detailed prediction numbers green for all muxes.

Gu21 is far too large an area to pontificate on local reception issues and/or field strengths / line of sight / diffracted etc.,.

Ideally, connect aerial direct to the Sony using a joiner to see if that cures the problem... i.e. no amplified signal. Y-splitters have 4dB attenuation to each leg -- so you have attenuators already.
Note powering off an amplified splitter will result in zero signal (unless there is direct cable pickup).

Sony's I've seen often have detailed tuning reception info with pre- and post- viterbi error correction numbers (rather or as well as a % Quality figure).

 

[monday]

Thanks again all for responses.
Rodders53, you have left me behind with 'prediction numbers for all muxes'. The Y-splitters were on the old 3-way splitter and part of the reason I changed to the new 8-way - they have now gone. The aerial feed in the roof is too far away to easily connect direct but I will follow up if necessary.

Last few days the set has behaved itself. I am just wondering now if the aerial engineer's visit on 17 June cured one fault, only for the atmospheric disturbance warned about on the BBC reception site from 23 June to take over. That disturbance may now have dispersed? But may be just a coincidence?
ericmark you may be right after all!

evdamadiynot: the aerial engineer's visit produced a new heavy duty lead so I think that is OK. Hopefully the set will continue to behave but watch this space.

 

[monday]

Well, here we are again. The signal disturbance has got worse these last few days - typically now a double interruption (interruptions 10s or so apart) now 3-4 times an evening. The BBC reception site shows reception on all relevant channels as good. Now that the hot weather seems to be over it would seem that the atmosphere is more stable? My sister tells me that my brother in law (who worked for the BBC and was responsible for setting up some of their mobile reception testing equipment in the 70's and 80's) always said that trees could be responsible for a lot of reception difficulties. Unfortunately, he is no longer around to ask, but could that still be the case? Lots of trees round here, including a Wellingtonia (Redwood) maybe 200-300 yards away.

 

[Rodders53]

I may well know said person (in a professional capacity) in either BBC Research or EID/Reception Advice. It was part of my job to use such kit at one time (90s) and advise trade and public on reception matters.

Full Postcode? One within 100 yards of your own (or metres) for a shop, pub, church or school will be fine. Will allow me to look at the reception detailed view for a spot nearer to your location and use Wolfbane for signal levels. Or PM me with it.

Trees are a possible cause of reception problems... always have been, always will.

Troubleshooting your Freeview Television reception | Help receiving TV and radio

Effects of poor Freeview reception are: loss of channels picture break up sound glitches/break up Step 1 – Check if there is a fault with your local transmitter First, use our Transmitter Checker tool. If there is a fault, it will be highlighted. If there is more than one transmitter...

www.bbc.co.uk

but hard to advise if that is the case with you.
Digital is often more tolerant of tree issues.

 

[Rodders53]

OK, for the PM'd postcode Wolfbane predicts 58 dBuV/m field strength at 10m (rooftop) level from CP. 61dBuV/m field from Guildford. Both have nominally clear line of sight between the aerials (excluding any trees or buildings).

Freeview (BBC spectrum planners) are all Green 100 or 99% of locations in the prediction grid square are Served (and Marginally served the same) so there's very, very low likelihood of weather-related (co-channel) interference. Ever.

CP at 70 degrees, Guildford 170 and Reigate 100 degrees are all going to be received to some extent on an aerial directed to CP so there's a lot of RF being received.

The ideal DTT receiver signal level is 45 - 65 dBuV terminated into a 75 ohms receiver. Some sets will work with lower signal levels, and some be happy with more. But outwith those levels is a potential problem.

Field strength + aerial gain + amplifier gain - splitter losses - cable losses - termination loss (1-2 dB) = signal at the receiver.

Aerial gain - say + 8dB (a lowish gain group A yagi).
https://maxview.co.uk/product/plug-in-signal-boosters/ if this is the unit in the loft then
Amplified splitter overall gain = +6 dB
10m cable loss = -2dB
Termination losses = - 2dB

58 + 8 = 66 + 6 = 72 - 2 = 70 - 2 = 68 dB = 3dB over the max.

Your cable and termination losses may be less, and your aerial may have more gain on some frequencies but nevertheless I would recommend fitting an attenuator on this TV's cable...
https://cpc.farnell.com/c/audio-vis.../attenuators-filters/tv-satellite-attenuators shows a selection.

A minimum of 6dB and more likely 10dB would be my suggestion. NB do not plug an attenuator directly into the TV's tuner socket; rather use short cables to and from the attenuator to reduce weight/leverage on the TV socket. TV tuner sockets are expensive to replace when damaged!

NB you stated that other TVs are fine with the relatively high signal levels.
NB2 Passive 8-way splitters should lose around 12dB of signal... and 66 from your aerial - 12dB = 54 dBuV which is slap bang in the middle of the ideal level.
Always assuming that Wolfbane's number is correct.

 

[monday]

Many thanks for the detailed assessment, much appreciated. I'll try a 10db in-line attenuator (with cables) and see what happens.

Just on your last point regarding other TV's. The other sets are all on the same powered 8-way splitter, or previously on a powered 3-way splitter. There would have been some attenuation on this 3-way because of the collection of Y-splitters attached to it; the reason I dumped it for the 8-way. So the signal reaching the other sets would be the same as the Sony set. Perhaps the older sets, only one of which is digital, are less sensitive to signal variation?

I'll report back.

 

[Rodders53]

Lets assume the last 3-way amplified splitter had +8dB gain. Any two-way splitter is -4 dB loss. Nett +4 dB over the 66 dB from aerial = 70dB. Again, the potential for overload on the new super-sensitive set...

You've marginally helped to lower signal level with the new box but not enough (probably).

Try an attenuator and see if things improve. NB Use the TV signal/quality meter on every multiplex frequency to check numbers before and after the attenuator is fitted. That data will probably be helpful.

https://www.sony.co.uk/electronics/support/articles/00094962#1._Digital_setup

 

[monday]

Thanks again. Attenuator and F-type plugs on order from CPC. I'll let you know what happens.