This is why EM interference can be an issue....

[berkeman]

TL;DR Summary

Good story about "fox hunting" for an interfering RF source

I've been on these "fox hunts" before, where you are trying to track down an interfering signal. We do them frequently for practice (as HAM radio operators), and have used the skills a few times for real. I haven't done it in the rain yet, though...

(CNN)For 18 months, residents of a village in Wales have been mystified as to why their broadband internet crashed every morning.

Now engineers have finally identified the reason: A second-hand television that emitted a signal that interfered with the connection.

https://www.cnn.com/2020/09/22/uk/old-tv-breaks-broadband-village-scli-intl-gbr/index.html

Engineers used a device called a spectrum analyzer and walked up and down the village "in the torrential rain" at 6 a.m. to see if they could locate an electrical noise, Jones said in a statement.
At 7 a.m. -- "like clockwork" -- the device "picked up a large burst of electrical interference in the village."

"The source of the 'electrical noise' was traced to a property in the village. It turned out that at 7 a.m. every morning the occupant would switch on their old TV which would in-turn knock out broadband for the entire village."

 

[Guineafowl]

Summary:: Good story about "fox hunting" for an interfering RF source

I've been on these "fox hunts" before, where you are trying to track down an interfering signal. We do them frequently for practice (as HAM radio operators), and have used the skills a few times for real. I haven't done it in the rain yet, though...



https://www.cnn.com/2020/09/22/uk/old-tv-breaks-broadband-village-scli-intl-gbr/index.html

I saw that story, too.

I assume by ‘old-fashioned TV’ they meant a CRT one; why would these generate more interference than a modern one?

What in the TV was making the interference - was it the local oscillator? There are no terrestrial services left in the UK, as far as I know, so the TV was presumably getting its signal from a digital box.

Finally, if the fault was so regular, why did it take them 18 months to find it?!

 

[Vanadium 50]

I suspect the problem was with the power supply.

 

[tech99]

I saw that story, too.

I assume by ‘old-fashioned TV’ they meant a CRT one; why would these generate more interference than a modern one?

What in the TV was making the interference - was it the local oscillator? There are no terrestrial services left in the UK, as far as I know, so the TV was presumably getting its signal from a digital box.

Finally, if the fault was so regular, why did it take them 18 months to find it?!

A CRT requires a line scan frequerency which is at about 16 kHz (625 system) and is delivered to the scan coils at around 25 Watts. Before the days when interfence from computers and broadband became so severe, line scan interference was very bad. It creates harmonics every 16 kHz right up the spectrum to VHF.
Further than this, the the scan coils vibrated to the frequency and created sound. This 16 kHz whistle was very audible to a teenager and nearly drove me nuts, whilst my parents could not hear it.

 

[Baluncore]

Once the investigators identified the source, the problem was fixed. The real problem with stories like this is that the critical details are not included. That is because the news media assume members of the general public would not understand.

The most disruptive and persistent stories are those with zero reliable facts. The mystery in the story is highlighted by the story teller, who keeps the key facts secret for as long as possible.
Rational analysis is not possible.

That one reporter can waste the time of so many people should be a crime.
In science, the key fact should be in the title, or in the abstract at the latest.

 

[Averagesupernova]

Engineers used a device called a spectrum analyzer...

Now every dummy with a laptop and audacity installed on it will think they can hunt down interference that they think they are and likely are not getting. 🤣

 

[JT Smith]

We have kind of the reverse problem. Since we don't watch very much TV we've shunned the expensive cable company and stuck with over-the-air TV for years. The number of channels is limited but it's worked okay... until the last few years. The number of channels we can get, even with excessive adjustment and moving of the indoor antenna, which we have replaced twice, has been steadily decreasing. Some channels are now completely gone; others are just too noisy. Some would probably have been watchable as degraded analog channels but a digital channel just falls apart when enough is missing.

We are perplexed as to why. Sometimes a channel looks good and then, without any rhyme or reason, we have to struggle to watch it at all. Streaming isn't that expensive. And we have access to free movies. But what's going on?

The conspiracy theory part of my human brain thinks that the cable company is somehow responsible. But it's probably some other source of modern interference. I just have no clue what. Our neighbors WIFI? Cell phones in cars driving by? Something from the nearby transit hub? I don't have, nor am I likely to think it affordable, to buy whatever hardware is necessary to track it down. I don't mind being in the rain. Is there some not-too-expensive way to debug this? Audacity??

 

[DaveE]

My spectrum analyzer doesn't go out in the rain.

 

[Baluncore]

The number of channels we can get, even with excessive adjustment and moving of the indoor antenna, which we have replaced twice, has been steadily decreasing. Some channels are now completely gone; others are just too noisy. Some would probably have been watchable as degraded analog channels but a digital channel just falls apart when enough is missing.

I assume those channels are analog TV, not digital TV. Analog channels are turned off as digital TV becomes available. Get an old digital TV, or a set top box.

The rise in the number of switching power supplies and home computers explains why AM radio and analog TV signals are deteriorating.

 

[Averagesupernova]

@JT Smith audacity is an audio analyzing program for computers. It is able to do spectral displays but obviously not into the RF region. I have a few old spectrum analyzers. A Cushman that will view up to a GHz, and an old HP that tops out at 110 MHz. I think I have a couple hundred bucks in the pair. And no, they won't be going out into the rain either.
-
I also find it odd that it took this long to solve. Chances are if it interferes with your WiFi, then the signal could be found on the spec-an with a suitable antenna at any location that the WiFi is wiped out.
-
I've chased spurious signals sliding around between 146.2 and 146.5 as the day progresses from early in the morning to late in the day. As the day went on and the defective paging transmitter warmed up the frequency of the spur changed. Talk about a pain tracking something down that isn't there all the time. I would have paid good money to have had a schedule to go by until I figured out that it was always somewhere around our 2M repeater input, just not always right on it.

 

[berkeman]

I also find it odd that it took this long to solve. Chances are if it interferes with your WiFi, then the signal could be found on the spec-an with a suitable antenna at any location that the WiFi is wiped out.

Yeah, that seemed a little strange to me too, since presumably the "final mile" of this distribution to the houses was wired. The houses are probably far enough apart that it would be hard for one EMI source to compromise all of their WiFi routers that were connected to a wired infrastructure, so I'm guessing that there is an RF link somewhere in the infrastructure that was getting stepped on before the cable distribution to the houses. It would take a better article to find that out.

One of the best "fox hunt" stories I've seen for a periodic interfering signal was in a neighborhood where an interfering signal would pop up every day at the same time for about 15 minutes and then go away. It's been long enough since I read the story that I don't remember what it was interfering with, but I seem to remember that it was very important like Police or EMS bands. The fox hunters were finally able to trace the signal to a house, and with the homeowner's help, they traced the signal to a wall clock. It turned out that the electric motor that turned the hour hand had a fault, and when it had to support the extra torque to lift the hour hand out of the 6 o'clock position, that caused it to put out the RF noise that was generating the EMI. Classic.

 

[JT Smith]

I assume those channels are analog TV, not digital TV. Analog channels are turned off as digital TV becomes available. Get an old digital TV, or a set top box.

Analog TV? That went away over a decade ago. Well, it did where I live anyway.


And yes, I know what Audacity is. I've got a copy on my computer for basic audio file manipulations. It does have a spectrum analyzer function but I don't think it's of any use for this particular problem.

 

[berkeman]

Analog TV? That went away over a decade ago.

Oh jeeze, has it been that long already? I guess so. Yeah the switch to digital TV was a bit difficult for us, since my wife is a minimalist and we were using over-the-air analog at the time. We were in an apartment at the time, so switching to a steerable digital TV indoor setup was challenging (hence my "hillbilly TV antenna" thread linked below).

So the quality of my over-the-air digital TV reception has been getting worse over the past few months. Probably the digital TV antenna that I'm using is getting old and starting to degrade. Last night I resorted to trying different reflector combinations to try to boost the signal for the horizontal UHF dipole antenna (inside the rotator disc on the top of the antenna unit). I could hand-hold it in a reasonable reflector position, but it was hard to figure out a way to mount it permanently.

So I went the fractal reflector route shown in the picture below (the antenna unit was already hanging from the ceiling). It actually worked a lot better than I expected, but it probably won't work for all stations (since you have to use the rotation function to find the best direction to point the UHF dipole in the disc -- the local stations are spread through about a 90 degree arc to my north.

Anyway, it looks like it's time to spring for a new over-the-air digital TV antenna. We live in a 2nd floor apartment and the TV is next to the balcony, so I could probably camouflage a fairly large antenna below the railing if that would help. (I already have a camouflage HAM radio antenna on the balcony). Does anybody have any suggestions for good digital TV antennas (USA models)? Clearly it needs to have rotational capability (or phased array capability, if that exists for digital TV antennas).

Thanks for any ideas!

View attachment 212357

 

[JT Smith]

Very creative. And I am not above "hillbilly" tactics.

But I'm more interested in what is affecting the previously acceptable signals. Some have degraded over time and others are degraded for shorter periods at what seems like random times. We have twice replaced the antenna, even trying one with an amplifier. Sometimes it doesn't matter where you stand holding it.

Something is interfering. I'd love to know what but have no idea how to figure it out.

 

[davenn]

Finally, if the fault was so regular, why did it take them 18 months to find it?!

The obvious assumption would be ... It didnt take 18 months to find, more likely it took 18 months for people
to finally complain to OFCOM about the problem ?

 

[berkeman]

I assume by ‘old-fashioned TV’ they meant a CRT one; why would these generate more interference than a modern one?

BTW, in addition to EMI problems from the power supply and deflection circuits, CRT based displays can undergo "tube arcs", although they are usually more transient and can be heard. But maybe this CRT had degraded to the point where it had a low-level tube arc going on that generated broad spectrum interference...

https://jestineyong.com/sparking-in-the-crt-tube-neck/

 

[JT Smith]

Yeah the switch to digital TV was a bit difficult for us, since my wife is a minimalist and we were using over-the-air analog at the time. We were in an apartment at the time, so switching to a steerable digital TV indoor setup was challenging (hence my "hillbilly TV antenna" thread linked below).

I looked it up and it was in 2009. I remember we came back from an overseas trip and our TV didn't work anymore. We knew the change was coming but, like your wife, we are also minimalists in certain ways.

We had a really old TV. It could only receive 15 channels or something like that. You selected which channels with thumbscrews! It did have remote though, it wasn't that old.

When the TV sound stopped working I plugged a computer speaker into the headphone jack of the TV and we watched it like that. Then the picture failed. So I got out my old 13" color TV from the basement and pulled the TV stand closer to the sofa. If it's closer the picture looks just as big!

But when they turned off the analog signals I had to give in. I couldn't find a converter box for sale anywhere and it's probably just as well. I bought a plasma TV and it's eleven years old now. At 42" it seemed huge then. Now it seems kind of small.

Still wish I knew what was messing up the signals. Something in the environment changed.

 

[Baluncore]

Something in the environment changed.

Or the coax cable is gradually filling up with water.

 

[Guineafowl]

Very interesting replies, thanks. I’m sure we’d all like to get a hold of that TV and see what’s happening.

The lack of technical details in the news is frustrating, but not unexpected. Journalists have butterfly intellects, like lawyers or politicians - able to show brief interest, then they flit on to the next subject, next case, or next department.

 

[JT Smith]

Or the coax cable is gradually filling up with water.

I think it would vinegar, right? So it wouldn't cause any problem.

 

[Baluncore]

I think it would vinegar, right? So it wouldn't cause any problem.

I don't understand. Vinegar?

 

[JT Smith]

Vinegar: an aqueous solution of acetic acid.

 

[Baluncore]

I think it would vinegar, right? So it wouldn't cause any problem.

I understand the term vinegar as a noun. You appear to use the term vinegar as a verb.

You need to explain what you mean. Where does the acetic acid come from?

 

[berkeman]

I haven't heard the term either, not even in HAM circles (other than maybe using salt and vinegar solutions to clean electrical contacts?)...

https://www.instructables.com/id/How-to-perfectly-clean-wires-in-minutes/

 

[JT Smith]

It was a typo. I left out the verb "be" in that sentence.

The vinegar comes my salad, the nearest liquid to the coax.

 

[Tom.G]

This was at least 30yrs. ago, when analog TV was normal.

We lived in an apartment building with other apartment buildings on each side of us. At one point we started getting severe TV interference that would occassionally wipe out the lower channels. Very annoying.

We had laying around, a 5 inch battery operated portable TV with continuous (analog) tuning knob, which also came with a schematic (not these days!). So I tapped into the AGC (Automatic Gain Control) circuit and brought it out to a jack; to which I connected a voltmeter and walked around the neighborhood.

Sure enough, the signal peaked at an adjacent building. I called the power company to ask them to track it down and kill the interference. They weren't interested.

I eventually realized that the usage pattern was similar to a microwave oven. That seemed quite strange since low TV channels start at 54MHz and microwave ovens are at 2.4GHz. The interference was gradually getting worse over a period of weeks, then disappeared.

My wild guess is the oven finally failed and was replaced with a new one.

So I ended up with a TV that served triple duty; a TV, a field strength meter, a manually tuned spectrum analyzer. It was eventually useful for initial emission testing before sending stuff to the testing lab.


Cheers,
Tom
(edit: added continuous tuning)

(classified as making lemonade when served a Lemon)

 

[waternohitter]

oh my... I love vinegar!

 

[Baluncore]

The vinegar comes my salad, the nearest liquid to the coax.

If you really had a problem you should not have dismissed the deterioration of coaxial cable by water absorption.

The dielectric constant of coaxial insulation is about 3. The dielectric constant of water is about 80. As they cyclically heat and cool, cables breath moist air in and out. Some of it stays.

When coaxial cables are important for power, or wide-band instrumentation, they are maintained at a constant positive pressure with dry nitrogen.

 

[JT Smith]

If you really had a problem you should not have dismissed the deterioration of coaxial cable by water absorption.

If you'd actually read and comprehended the thread you would have seen that this was unlikely. I said that the antenna were indoor, had been replaced twice, and that some of the interference was sporadic. New antenna come with new cables. You have no idea of the humidity level where I live or the amount of salad dressing I spill for that matter. It's just so off the wall a suggestion as to make me think you're just screwing with me for some reason. I hope not.

I think this thread should be locked.

 

[berkeman]

I think this thread should be locked.

Nah, but we can all agree to stop the side digression about vinegar and water. At least I understood the water part.

 

[rude man]

We have kind of the reverse problem. Since we don't watch very much TV we've shunned the expensive cable company and stuck with over-the-air TV for years. The number of channels is limited but it's worked okay... until the last few years. The number of channels we can get, even with excessive adjustment and moving of the indoor antenna, which we have replaced twice, has been steadily decreasing. Some channels are now completely gone; others are just too noisy. Some would probably have been watchable as degraded analog channels but a digital channel just falls apart when enough is missing.

We are perplexed as to why. Sometimes a channel looks good and then, without any rhyme or reason, we have to struggle to watch it at all. Streaming isn't that expensive. And we have access to free movies. But what's going on?

The conspiracy theory part of my human brain thinks that the cable company is somehow responsible. But it's probably some other source of modern interference. I just have no clue what. Our neighbors WIFI? Cell phones in cars driving by? Something from the nearby transit hub? I don't have, nor am I likely to think it affordable, to buy whatever hardware is necessary to track it down. I don't mind being in the rain. Is there some not-too-expensive way to debug this? Audacity??

You should probably get an outdoor yagi antenna unless you're very close to the stations. They may have reduced power for some reason.

 

[rude man]

I assume those channels are analog TV, not digital TV. Analog channels are turned off as digital TV becomes available. Get an old digital TV, or a set top box.

The rise in the number of switching power supplies and home computers explains why AM radio and analog TV signals are deteriorating.

Analog tv signals are practically gone.

 

[Baluncore]

Analog tv signals are practically gone.

The number of channels is limited but it's worked okay... until the last few years.

This was over years, just like some of the channels were analogue.

But there is little point in discussing systems that use indoor antennas, they are designed for looks, not performance.

Often the VHF / UHF band changed with the A-D transition.
And a room is frequency sensitive, a cavity backed slot.

 

[berkeman]

But there is little point in discussing systems that use indoor antennas, they are designed for looks, not performance.

Sort of. The Fractal Antenna Reflector post that I linked above was in an apartment. You are not allowed to drill holes in the walls to make coax feedthroughs when you live in an apartment. I did have attic access (very tiny), so I did briefly consider trying to route something through the attic, but not for long.

 

[Baluncore]

The Fractal Antenna Reflector post that I linked above was in an apartment.

Where was that link ?