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Author Topic: Well, This is the Lighter Side.......  (Read 651 times)
SandTEngineer
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« on: June 01, 2020, 09:22:43 am »

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Ofcom shine a light on interference issue:

Ofcom (the UK telecoms regulator) spectrum assurance team were contacted by National Air Traffic Services to inform them that aircraft flying in and out of Glasgow airport were being affected by interference when they were between 6000 and 10 000 feet (1800m to 3000m) in the air. The interference was affecting voice communications between the controllers on the ground and the aircraft. The interference was traced to a house directly underneath the flightpath of the aircraft with the cause being four ‘vintage’ lightbulbs that the homeowner had recently bought online. Due to the construction of the bulbs, they were found to be radiating a ‘noise’ when they were switched on that affected a wide range of licensed spectrum. The bulbs were removed from the sockets and checks with NATS and aircraft operators confirm that the area is now free of interference. The lightbulb suppliers were contacted to make sure the bulbs are not sold to any more unwitting customers. In the case of any interference to operational train radio equipment the radio spectrum manager should always be informed to carry out an investigation.
Grin
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eightf48544
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« Reply #1 on: June 01, 2020, 11:03:31 am »

People worry about 5G but those lamps must have been pretty powerful to affect planes at 1800 to 3000 m.
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grahame
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« Reply #2 on: June 01, 2020, 11:50:01 am »

People worry about 5G but those lamps must have been pretty powerful to affect planes at 1800 to 3000 m.

Not sure I totally agree ... it's affected signals between the ground and planes at those heights - the interference would probably be at a much lower altitude.
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stuving
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« Reply #3 on: June 01, 2020, 12:45:26 pm »

People worry about 5G but those lamps must have been pretty powerful to affect planes at 1800 to 3000 m.

Not sure I totally agree ... it's affected signals between the ground and planes at those heights - the interference would probably be at a much lower altitude.

If it was actually modulating the propagation path, it really would need to be powerful! From the description, it could be entering a ground station receiver, which could be close to the house, and not much power would be needed. But it's not impossible for it to be getting into the aircraft's receiver. These days a lot of things convert all their power between various flavours of AC and DC by putting it through what is essentially a transmitter (i.e. a powerful oscillator).
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broadgage
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« Reply #4 on: June 01, 2020, 12:51:14 pm »

No good will come from these new fangled flying machines, nor from electric lights.

We should return to gas lights, oil lamps, horses, and steam powered railways.
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A proper intercity train has a minimum of 8 coaches, gangwayed throughout, with first at one end, and a full sized buffet car between first and standard.
It has space for cycles, surfboards,luggage etc.
A 5 car DMU is not a proper inter-city train. The 5+5 and 9 car DMUs are almost as bad.
Electric train
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« Reply #5 on: June 01, 2020, 02:11:15 pm »

Quote
Ofcom shine a light on interference issue:

Ofcom (the UK telecoms regulator) spectrum assurance team were contacted by National Air Traffic Services to inform them that aircraft flying in and out of Glasgow airport were being affected by interference when they were between 6000 and 10 000 feet (1800m to 3000m) in the air. The interference was affecting voice communications between the controllers on the ground and the aircraft. The interference was traced to a house directly underneath the flightpath of the aircraft with the cause being four ‘vintage’ lightbulbs that the homeowner had recently bought online. Due to the construction of the bulbs, they were found to be radiating a ‘noise’ when they were switched on that affected a wide range of licensed spectrum. The bulbs were removed from the sockets and checks with NATS and aircraft operators confirm that the area is now free of interference. The lightbulb suppliers were contacted to make sure the bulbs are not sold to any more unwitting customers. In the case of any interference to operational train radio equipment the radio spectrum manager should always be informed to carry out an investigation.
Grin

Ofcom website https://www.ofcom.org.uk/about-ofcom/latest/features-and-news/interference-issue

Seems strange that a 60W incandescent lamp that looking at the photo seems to have a tungsten element coauld cause interference, I would have been more inclined to look for dimmers in the circuit; especially if they had dimmers meant for LED lamps

Also the lamp is marked "CE" also known as China Export   Grin Grin
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broadgage
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« Reply #6 on: June 01, 2020, 04:26:46 pm »

If the lamp pictured in the report is one of the ACTUAL lamps that caused the interference, then yes it would appear to be a modern reproduction of an older type of tungsten lamp.
A mains voltage voltage tungsten lamp needs a filament of considerable length. In modern lamps this is coiled, and sometimes the coil is again coiled, so as to fit easily into the bulb.

Older types of tungsten lamp, and modern reproductions thereof, did not coil the filament but instead arranged it as a complex zig-zag up and down the bulb. Correctly known as a "squirrel cage filament" and favoured for ships navigation lights as well as decorative uses. Very wasteful of electricity.

In view of the poor standards of technical reporting these days, I consider it possible that the lamp illustrated is NOT the actual lamp but may be a library image found by googling "vintage bulb"

If the picture is accurate, then yes, squirrel cage filament lamps CAN cause radio interference. Parts of the lamp can function as a very crude thermionic valve and may oscillate and radiate interference. This is well documented in old textbooks dating from the era when such lamps were popular.
Apparently trivial differences between one lamp and another, well within normal manufacturing tolerances, can result in some examples radiating interference whilst others do not.

Alternatively, the actual lamps involved might have been LED types, with strips of LEDs arranged so as to somewhat simulate a squirrel cage tungsten lamp. The LEDs cant produce interference, but the switched mode driver circuits can be a cause of significant radio interference.

In either case, the interference radiated DIRECTLY from a relatively small lamp is unlikely to be significant. The supply wire to the lamp can act as an aerial, and if fortuitously aligned, high up, and of the optimum length could radiate significant interference.
In most cases I doubt that it would be significant, but with a sufficient number of lamps in use, eventually some particularly bad examples will end up in a loft conversion, under a flight path, and connected to wire exactly the correct length to act as an effective aerial.
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A proper intercity train has a minimum of 8 coaches, gangwayed throughout, with first at one end, and a full sized buffet car between first and standard.
It has space for cycles, surfboards,luggage etc.
A 5 car DMU is not a proper inter-city train. The 5+5 and 9 car DMUs are almost as bad.
Clan Line
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« Reply #7 on: June 01, 2020, 04:43:06 pm »


In view of the poor standards of technical reporting these days,

.......... including from Ofcom  -  "aircrafts"  indeed  !!!!!  Good job that there weren't sheeps on the runway too......
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stuving
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« Reply #8 on: June 01, 2020, 05:13:02 pm »


In view of the poor standards of technical reporting these days,

.......... including from Ofcom  -  "aircrafts"  indeed  !!!!!  Good job that there weren't sheeps on the runway too......

That would be their PR people, no doubt (would that function be called "Communications", even in Ofcom?). I hope we can trust that their investigations staff did know what they were doing, and confiscated the right thing. And since they provided a screen shot of the analyser, we can probably trust that they also took one of the actual bulb.

The spectrum is the right shape for some form of wideband FM, centred on 119.8 MHz with deviation 2.6 MHz. (The Aeronautical Mobile allocation is 117.975 - 137 MHz.) You can't tell from a single display what the modulating waveform was, and of course this may be a harmonic of the primary oscillation.

In the bulb pictured, the two leads are pretty close to each other, with the full mains voltage between them - so Broadgage's idea of it behaving like a thermionic valve could work. Add a bit of gas, and a resonator involving the impedance of the wiring in its mains feed, and almost anything could happen. Perhaps it was originally made for 120 V, and worked fine, but when rejigged for 240 V ...
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old original
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« Reply #9 on: June 02, 2020, 12:51:11 pm »

No good will come from these new fangled flying machines, nor from electric lights.

We should return to gas lights, oil lamps, horses, and steam powered railways.

...and full size trains with comfy seats and full buffet / bar  😁
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GBM
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« Reply #10 on: June 02, 2020, 01:33:30 pm »

Tin hats on folks, the door's been left wide open... Grin Grin
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TonyK
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« Reply #11 on: June 02, 2020, 02:12:21 pm »


That would be their PR people, no doubt (would that function be called "Communications", even in Ofcom?). I hope we can trust that their investigations staff did know what they were doing, and confiscated the right thing. And since they provided a screen shot of the analyser, we can probably trust that they also took one of the actual bulb.

The spectrum is the right shape for some form of wideband FM, centred on 119.8 MHz with deviation 2.6 MHz. (The Aeronautical Mobile allocation is 117.975 - 137 MHz.) You can't tell from a single display what the modulating waveform was, and of course this may be a harmonic of the primary oscillation.

In the bulb pictured, the two leads are pretty close to each other, with the full mains voltage between them - so Broadgage's idea of it behaving like a thermionic valve could work. Add a bit of gas, and a resonator involving the impedance of the wiring in its mains feed, and almost anything could happen. Perhaps it was originally made for 120 V, and worked fine, but when rejigged for 240 V ...

Almost 40 years ago, my very first video recorder used to occasionally start playing an annoying jingle during the evenings, which I later tracked down using teh shortwave setting on my then car radio to be "La Voix d'Allemagne", an East German French language propaganda radio station. I tried retuning the RF output to the TV and a few other things, which made no difference. This interference didn't appear when playing back recorded programmes. Eventually, there being no internet then, I contacted an office in Bristol of the Home Office radio licensing people. Someone came round and shortened the incoming TV aerial lead by a few inches. We couldn't test it really because the interference only happened on still evenings and he worked days, but it certainly helped.

Over the inevitable cup of tea, he told me a few of the anecdotes that people in such an occupation collect over the years, much as we all do. One concerned a lady somewhere else in the country who had troubles of interference that nobody could fathom, not even with all the Ghostbusters equipment available to them. They visited a few times to find no problem, and were beginning to think it was in the lady's head when someone arrived in the evening. The problem started as soon as she turned on the light, and the engineer rightly connected the cause with the effect. The bulb was changed, problem gone forever. The officer carefully took the bulb back to the office, and had a laboratory look at it. They reckoned that the filament had bust at some time, with the larger broken piece swinging back to weld itself to the remaining bit in a different place before anyone noticed a problem, so making an amplifier that received a certain signal and re-transmitted it at a different frequency. The bulb ended up in some museum of astonishing household items that had reconfigured themselves to serve a new purpose. I had forgotten all about this until today. I might have explained the science a bit wrong, and might try to look it up, given that we have since invented the internet.

Edinburgh Approach is 121.200 MHz if you want to listen in.

No good will come from these new fangled flying machines, nor from electric lights.

We should return to gas lights, oil lamps, horses, and steam powered railways.

...and full size trains with comfy seats and full buffet / bar  😁

"During the war..."
« Last Edit: June 02, 2020, 03:00:37 pm by TonyK » Logged

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