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Old 10th Jul 2021, 9:08 pm   #21
Refugee
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Default Re: RF interference from a filament bulb

Some line output valves had a band around the glass to stop the unwanted oscillations
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Old 10th Jul 2021, 10:51 pm   #22
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Default Re: RF interference from a filament bulb

Years ago I read some long forgotten report on how after WW2, some Chain High ( or even Low ) RADAR stations were brought out of mothballs in light of the emerging cold war threat.
One south coast station experienced puzzling intermittent receive noise which upon lengthy investigation was traced to a Tungsten lamp in the duty room Lavatory, hence explaining the intermittent nature of the fault.

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Old 10th Jul 2021, 11:42 pm   #23
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Default Re: RF interference from a filament bulb

From the Radiomuseum. An essay about oscillations in filament lamps:
http://www.radiomuseum.org/forum/rus...surements.html

DFWB.
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Old 13th Jul 2021, 10:13 am   #24
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Default Re: RF interference from a filament bulb

I have only come across the effects of Barkhausen-Kurz oscillations from TV line output stages a few times during my years in the trade. The symptoms gave a sparkling white vertical band of interference on the left hand side of the screen.

The first was on a BRC 1500 black and white chassis which was traced to the 30FL2 line oscillator valve, and a few times on the same chassis it was down to the Line Output valve screen feed decoupling capacitor.
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Old 13th Jul 2021, 10:30 am   #25
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Default Re: RF interference from a filament bulb

I wonder how many interference problems which were never traced, despite serious effort, may have been light bulbs and not considered as being 'impossible'?

The famous one being Cobra Mist, but I understand that one followed the pulses and frequency of the transmitter, so it's very unlikely.

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Old 13th Jul 2021, 12:24 pm   #26
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Default Re: RF interference from a filament bulb

It's veering away from the original context a bit, but I do recall that very occasionally you'd hear a filament lightbulb whining and tapping it would generally stop it, sometimes turning it through 180 degrees would be necessary to stop it repeating- presumably a high harmonic of mains frequency being excited by chance mechanical filament characteristics. As mentioned, everything has at least one resonance awaiting provocation!
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Old 13th Jul 2021, 1:40 pm   #27
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Default Re: RF interference from a filament bulb

I recall as a child being shown a relatives workplace that was involved in some form of radio related research, possibly classified.

Several rooms were lit by 6 volt vehicle headlight bulbs, in series groups of four from a large 25 volt transformer. "to prevent interference" The nearby corridors were gas lit.
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Old 21st Jul 2021, 10:26 pm   #28
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Default Re: RF interference from a filament bulb

Hi.

In the past I recall a few occasions where you could hear the filament lamp singing possibly in the several kHz region. More often than not the lamp failed shortly after. This seems to be due to a minute break in the filament as per what GMB was saying in post #11. As it must have been arcing across the break, there would no doubt be significant RF interference.

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Old 22nd Jul 2021, 5:21 pm   #29
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Default Re: RF interference from a filament bulb

Quote:
Originally Posted by rambo1152 View Post
OK, I'll bite.
This is the context we have to go on.
https://www.ofcom.org.uk/about-ofcom...rference-issue

That style of writing is something I expect from the Daily Mail, not a government-approved regulatory body.

Given the non-academic style, is there any evidence the image of the tungsten filament lamp is the actual lamp in the case, and not a random stock image?

In the absence of a proper report, all bets are off.
The bulb in this ofcom report was not an incandescent type it was a modern "vintage" replica almost certainly using LED's.
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Old 22nd Jul 2021, 5:23 pm   #30
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Default Re: RF interference from a filament bulb

Filament lamps can "ring" but I have always put this down to the dimmer pulsing the filament.
Mike
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Old 22nd Jul 2021, 11:18 pm   #31
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Default Re: RF interference from a filament bulb

Couldn't help noticing how when filament bulbs are dimmed, the bulb itself seems to make an audible noise, it clearly vibrates for it to do this, how interesting.
Suddenly a piece of old fashioned junk has now become something of a case study.
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Old 23rd Jul 2021, 1:51 pm   #32
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Default Re: RF interference from a filament bulb

Coincidentally, the 12V quartz bulb in my reading lamp has just started singing softly when it is turned on in either of its two brightness levels. It is a standard-type lamp with the transformer in the base, so the noise must be coming from the bulb. I have tried removing the bulb and cleaning the pins but it made no difference. A quick check with my tranny showed no interference being generated on any waveband (FM, LW, MW or SW).
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