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Old 09-23-2020, 08:38 AM   #1
hazel
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Did you know that an old TV set can wreck a whole village's broadband?


It happened recently in a Welsh village called Aberhosan. They had dreadful broadband reception. You had to log in very early in the morning to get a decent speed. Yet BT Openreach engineers couldn't find anything wrong. All their tests showed that the network was working perfectly.

Finally they tried a spectrum analysis technique called Single High-level Impulse NoisE (SHINE) and discovered an interference signal that started at exactly 7.00 AM. They traced it to a specific house, where they discovered an old TV set that was switched on every morning at 7.00 to watch the morning news. The set was switched off permanently and the problem was solved. BT are not giving out the offending address for obvious reasons.

You can read the whole story at https://www.openreach.com/news/secon...entire-village. What it doesn't explain (and what I would very much like to know) is what specifically that TV set was doing that TV sets in general don't do. Any ideas?

Last edited by hazel; 09-23-2020 at 08:40 AM.
 
Old 09-23-2020, 09:15 AM   #2
smallpond
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Impulse noise probably means that there was arcing from the high voltage flyback circuit needed for a CRT. This generates short pulses across a wide spectrum. Modern non-CRT TVs won't have this problem.
 
Old 09-23-2020, 09:31 AM   #3
hazel
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I take it that by "modern non-CRT TVs", you mean those flat screens that look like giant flat-screen monitors.
 
Old 09-23-2020, 10:10 AM   #4
smallpond
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I used to work for a company that made CRT monitors. Not only did they use potentially lethal high voltage, but a 21" glass CRT bottle contains about 5 pounds of lead to keep the X-rays that it generates from frying its users. Thanks, Mom, for all those times you said "Don't sit too close to the TV".

Flat screens don't have those specific problems, but they still use some wonderfully toxic chemicals, so still have serious disposal issues.
 
Old 09-23-2020, 10:13 AM   #5
michaelk
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Anything that receives a RF signal has the potential to interfere with another RF signal i.e. AM/FM radios, any TV that can receive an over the air broadcast station including smart TVs, computers, laptops, mobile phones, cordless phones, baby monitors, wifi devices. The signal decoder is also a small signal rf generator and in most cases is small enough not to interfere with anything else.

If some electronic component breaks etc. that could cause interference to other nearby devices. The jamming signal would have to be large and on the right frequency to take out the entire village but it is possible.

I don't think x-rays interfere with RF signals.

Last edited by michaelk; 09-23-2020 at 10:14 AM.
 
Old 09-23-2020, 10:20 AM   #6
cynwulf
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Quote:
Originally Posted by hazel View Post
I take it that by "modern non-CRT TVs", you mean those flat screens that look like giant flat-screen monitors.
I found the "modern non-CRT TVs" to be quite self explanatory.
 
Old 09-23-2020, 12:48 PM   #7
fatmac
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So, BT Openreach must have cut some corners when setting up their wifi system, for an old TV to cause it problems....
 
Old 09-23-2020, 02:20 PM   #8
sgosnell
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Any excuse is better than none...
 
Old 09-24-2020, 03:07 AM   #9
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Quote:
Originally Posted by fatmac View Post
So, BT Openreach must have cut some corners when setting up their wifi system, for an old TV to cause it problems....
Openreach maintain the broadband fibre/copper network and exchanges, as I recall, nothing to do with wifi.
 
Old 09-24-2020, 04:13 AM   #10
fatmac
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They set up the customer wifi systems too, (don't they), if I remember right, it was them that set ours up.

(Ditched years ago in favour of Virgin, I hasten to add.)

Last edited by fatmac; 09-24-2020 at 04:16 AM.
 
Old 09-24-2020, 04:32 AM   #11
cynwulf
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Quote:
Originally Posted by fatmac View Post
They set up the customer wifi systems too, (don't they), if I remember right, it was them that set ours up.
Not to my knowledge. You get a router in the post and you plug it in and off you go.

If you have phone line trouble they get called out (via your provider, whether it's BT or anyone else using the BT lines) and if the fault turns out to be in your property, you can get landed with a big call out charge.
 
Old 09-24-2020, 05:34 AM   #12
business_kid
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It doesn't surprise me much.

Some places use microwave (or lower frequencies) for Internet. I had it for a decade at least. The isp sticks a transmitter on a mountain top; Each customer gets an aerial on the roof, a bit of gear in the attic and that's it. Or it could be received & distributed by cable.

OTOH, really old telly's using a tube instead of an LCD screen used close to a KW of power. Most of that went to the Line Output stage. An important stage was the Line output, where a few hundred volts was driven at 15.625 khz, turning out 7.5 - 9.0 KV! In the early ones, this was then put into a 'tripler' - a circuit of diodes and capacitors connected as voltage doubler, They were usually x5 at least, but the losses actually meant you got out x3 = ≅25KV. This was required for the front of the screen. No sine waves, this stuff was very rich in harmonics. Frankly, I'm not the least bit surprised. I'm surprised the old TV is still working that's all. Some old tv or audio guy must have been propping it up with vintage parts. It would have to be pre-1980. That's old.

In the 1980s, power went down, to 7KV for the 1st stage, 21KV and about 200Watts, but they were still electrically noisy!

Last edited by business_kid; 09-24-2020 at 05:52 AM.
 
Old 09-24-2020, 05:59 AM   #13
petelq
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the UK is completely digital now (for tv) so the old folk would need to use the old tv as a monitor with a freeview box. Of course, that would still churn out whatever interference it was causing.
The family of the couple are doubtful of openreach's conclusions. They say that the second hand tv was acquired recently and that the interference has been happening for longer.
 
Old 09-24-2020, 06:01 AM   #14
hazel
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A lot of digital TVs still use a CRT for their display. Mine does.
 
Old 09-24-2020, 07:46 AM   #15
petelq
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Quote:
Originally Posted by hazel View Post
A lot of digital TVs still use a CRT for their display. Mine does.
I stand corrected. I thought that the only crt screen tvs left, needed to plug into a digital box to function.
 
  


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