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Smart TV reporting "no signal"

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bungeejumper
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Smart TV reporting "no signal"

#406760

Postby bungeejumper » April 25th, 2021, 11:05 am

Spoiler, I've solved this one now - on an operational level, anyway - but I would still quite like to know what happened?

The other night, our LG smart TV gave a black screen and reported "no signal" on its default terrestrial mode when I first switched it on. (It worked perfectly on t'interweb, though.) After much rummaging and cable-replugging, I eventually found that a power connection to my signal amplifier had gone dodgy. I cleaned up the socket, and normal service was resumed.

But back in the good old days, even a really crappy incoming signal (or an un-amplified signal) would have been enough to create a bit of visual fizz and crackle and interference on the TV screen, so that I could experiment and try and improve things. This TV, however, seemed to be saying "if your signal isn't 100% I'll go blank and pretend I can't see it at all."

Is that because the TV is digital, or because the terrestrial signal is digital, or because the signal amplifier has introduced some kind of all-or-nothing element to the game?

Just wondering. Anybody?

BJ

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Re: Smart TV reporting "no signal"

#406806

Postby XFool » April 25th, 2021, 1:01 pm

bungeejumper wrote:But back in the good old days, even a really crappy incoming signal (or an un-amplified signal) would have been enough to create a bit of visual fizz and crackle and interference on the TV screen, so that I could experiment and try and improve things. This TV, however, seemed to be saying "if your signal isn't 100% I'll go blank and pretend I can't see it at all."

Is that because the TV is digital, or because the terrestrial signal is digital...

Yep.

mc2fool
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Re: Smart TV reporting "no signal"

#406807

Postby mc2fool » April 25th, 2021, 1:06 pm

bungeejumper wrote:Is that because the TV is digital, or because the terrestrial signal is digital, or because the signal amplifier has introduced some kind of all-or-nothing element to the game?

In this case, as your TV had reported "no signal", it's almost certainly the latter ... unless your TV reports that when what it actually means is "signal is too weak and/or noisy to decode".

Digital TV is almost all or nothing, i.e. either you get a good picture or you get a black screen, with a narrow bit inbetween where you get a picture but with lots of pixelation (blockiness), freezes, and other visual "coughs and splutters" (so to speak), and that's down not only to signal strength but also the quality of the signal (e.g. if there's a lot of noise).

Your TV will almost certainly have, somewhere in its setting, etc, a signal strength "meter" which shows both strength and quality.

pochisoldi
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Re: Smart TV reporting "no signal"

#406809

Postby pochisoldi » April 25th, 2021, 1:20 pm

https://en.wikipedia.org/wiki/Cliff_effect

This effect can most easily be seen on digital television, including both satellite TV and over-the-air terrestrial TV. While forward error correction is applied to the broadcast, when a minimum threshold of signal quality (a maximum bit error rate) is reached it is no longer enough for the decoder to recover. The picture may break up (macroblocking), lock on a freeze frame, or go blank.

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Re: Smart TV reporting "no signal"

#406820

Postby bungeejumper » April 25th, 2021, 2:04 pm

pochisoldi wrote:https://en.wikipedia.org/wiki/Cliff_effect

This effect can most easily be seen on digital television, including both satellite TV and over-the-air terrestrial TV. While forward error correction is applied to the broadcast, when a minimum threshold of signal quality (a maximum bit error rate) is reached it is no longer enough for the decoder to recover. The picture may break up (macroblocking), lock on a freeze frame, or go blank.

I think you've nailed it there, pochisoldi. Much thanks. :D

BJ

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Re: Smart TV reporting "no signal"

#406830

Postby mc2fool » April 25th, 2021, 2:58 pm

bungeejumper wrote:
pochisoldi wrote:https://en.wikipedia.org/wiki/Cliff_effect

This effect can most easily be seen on digital television, including both satellite TV and over-the-air terrestrial TV. While forward error correction is applied to the broadcast, when a minimum threshold of signal quality (a maximum bit error rate) is reached it is no longer enough for the decoder to recover. The picture may break up (macroblocking), lock on a freeze frame, or go blank.

I think you've nailed it there, pochisoldi. Much thanks. :D

BJ

Pretty much what I said. ;)

But you can test what your TV saying "no signal" actually means pretty simply. First find the signal strength & quality indicator in the set and note what it says:

a) under normal working conditions,
b) with the power connection to your signal amplifier unplugged (i.e. your originally reported fault), and
c) with the aerial lead going directly to the TV (instead of through the signal amplifier)

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Re: Smart TV reporting "no signal"

#406894

Postby AF62 » April 25th, 2021, 8:11 pm

[quote="bungeejumper"]But back in the good old days, even a really crappy incoming signal (or an un-amplified signal) would have been enough to create a bit of visual fizz and crackle and interference on the TV screen,/quote]

Back in the good old days I didn’t need an aerial plugged into the TV to get a watchable picture - perhaps because I can see the mast from my front door 10 miles away which was broadcasting at thousands of kW (and people worried about mobile phone masts!).

These days the HD channels broadcast from that transmitter have recently disappeared from the TV, seemingly due to poor reception. No matter, the TV has a satellite input as well so I just swap over to that.

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Re: Smart TV reporting "no signal"

#407033

Postby XFool » April 26th, 2021, 10:59 am

AF62 wrote:Back in the good old days I didn’t need an aerial plugged into the TV to get a watchable picture - perhaps because I can see the mast from my front door 10 miles away which was broadcasting at thousands of kW (and people worried about mobile phone masts!).

These days the HD channels broadcast from that transmitter have recently disappeared from the TV, seemingly due to poor reception.

Sounds unlikely - assuming it IS your DTT transmitter. But then again, is your DTV tuner actually tuned to that source? You need to check, it may have been grabbed by some far away DTT source. It happens. :(


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