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Ofcom trace interference to a lightbulb

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John Lee24/09/2020 11:47:49
804 forum posts
93 photos

Full size related but it just goes to show how interference can be generated from an unexpected source. Ofcom link

Peter Christy24/09/2020 12:03:03
1908 forum posts

On a similar note: **LINK**

surprise

--

Pete

Bob Cotsford24/09/2020 12:04:11
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8798 forum posts
494 photos

How does that bulb work, some form of arc? Remember the crude spark gap transmitters (I only know of them from museums, honest disgust )

Capt Kremen24/09/2020 12:39:24
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391 forum posts
154 photos

These type of interference are not as isolated as might seem.

Commercial ovens e.g. Baker's, Confectioners, Biscuit Makers etc. etc. switch these on and off at often set times coinciding with work patterns and shifts. A dodgy connection or two in these or some other component misbehaving, (and other equipment), can easily generate disruptive signals.

Maybe your clubmate 'Old Joe' did suffer a radio glitch on 2.4 after all!

Geoff S24/09/2020 13:17:11
3830 forum posts
49 photos
Posted by John Lee on 24/09/2020 11:47:49:

Full size related but it just goes to show how interference can be generated from an unexpected source. Ofcom link

That's a very strange light bulb with an ES (Edison Screw) connector. I was involved with selling light bulbs in our family electrical/radio etc shop from childhood in the 1940s onwards and all mains light bulbs were bayonet fittings. Thiis was at a time when many houses had gas rather than electric lighting (and no indoor plumbing) in our small mining town. The only screw fitting bulbs we sold were MES (Miniature Edison Screw) bulbs for torches and bike lamps.

I can only assume there was a loose connection to the filament or perhaps a mechanical connection that wasn't really secure and thus generated a spark. As Bob mentioned early radio transmitters used spark gaps to generate the RF - and that's not so long ago in real terms. I bet it was an interesting investigation and very satisfying to bring it to a successful conclusion.

On the old TV interference I'm guessing it was a valve one with a CRT which needed several kilovolts for the EHT and again the source of the interference was a spark.

Geoff

kc24/09/2020 13:33:46
6730 forum posts
174 photos

That 'vintage' lightbulb might have been a modern one made to look vintage! But ES bulbs were common back in the 1950.s and 60's - they were used in things such as photoflood lights, photographic enlargers & projectors. Probably used in industrial stuff too where more accurate location of the bulb was needed . Lots of items now use ES bulbs if they come from places like Ikea etc.

Kevin Wilson24/09/2020 13:35:22
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403 forum posts
13 photos

Most mains powered equipment that have low voltage circuits use switch mode power supplies (SMPS) to generate the low voltages. These SMPS use frequencies typically in the 30>40kHz range in the conversion process. The cheaper units have very poor filtering and cause huge amounts of harmonic energy across the RF spectrum.

Its a big problem for radio amateurs such as myself. Mains powered LED lamps are a particular problem, probably due to being so ubiquitous and built to the cheapest, lowest standard.

Kevin Wilson24/09/2020 13:41:30
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403 forum posts
13 photos

As KC notes, with the increase in worldwide transport of electrical fittings ES27 lamps (and ES14) are not uncommon. Decorative light fittings are frequently ES or SES.

Geoff S24/09/2020 14:56:36
3830 forum posts
49 photos
Posted by Kevin Wilson on 24/09/2020 13:41:30:

As KC notes, with the increase in worldwide transport of electrical fittings ES27 lamps (and ES14) are not uncommon. Decorative light fittings are frequently ES or SES.

That's true now but back in 1950s and 60s they were almost unknown in a domestic setting. I much prefer bayonet fittings myself as they're much easier and quicker to fit.

A good point about LED light fittings which have switch mode regulators (and rectifiers) to convert 240v ac to 12v dc or whatever for the LEDs. I'm sure they could well generate all sorts of RF interference. I think eventually houses will be wired with a 12 dc circuit for lighting with a central ac to dc regulator/rectifier and much simpler (and probably cheaper) LED bulbs with greatly extended life.

Geoff

Martin_K24/09/2020 15:29:44
206 forum posts

The photo in the Ofcom article, linked below, looks like an incandescent bulb. Interesting as they have not been legally for sale in the UK or EU for many years.

Possibly it is a reproduction "Mazda" (General Electric brand) bulb.

The interference from these was known about 70 years ago.

kevin b24/09/2020 15:33:07
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1934 forum posts
152 photos

A good point about LED light fittings which have switch mode regulators (and rectifiers) to convert 240v ac to 12v dc or whatever for the LEDs. I'm sure they could well generate all sorts of RF interference. I think eventually houses will be wired with a 12 dc circuit for lighting with a central ac to dc regulator/rectifier and much simpler (and probably cheaper) LED bulbs with greatly extended life.

Geoff

Good idea Geoff.

Then in the future when power supplies fail because of demand due to vehicle charging, we will at least be able to read RCM&E magazine if we plug our lipos into the house lighting circuit.

devil

Martin Harris24/09/2020 15:41:28
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9558 forum posts
258 photos

Far from being a rarity, I think the lamps* ("Bulbs? Bulbs is wot you plant in your garden" was indelibly knocked into me by our storemen at work) used in my house have at least reached parity between ES and bayonet and I suspect ES are well in the majority.

*Full title: Lamps, incandescent.

Edited By Martin Harris on 24/09/2020 16:02:01

Simon Chaddock24/09/2020 15:46:38
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5795 forum posts
3063 photos

Could the great length (300 mm?) of that single strand filament in that bulb be significant rather than the much shorter "coiled coil" used in a conventional incandescent bulb.

I don't know ES or SES fittings are that rare in the UK. I have an ES in my desk lamp and all oven bulbs are SES as far as I am aware. wink 2

Martin Harris24/09/2020 16:12:18
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9558 forum posts
258 photos

The link hidden at the bottom of Martin_K's post gives a very plausible explanation...essentially, yes - the filament length is at the root of the phenomenon.

Steve J24/09/2020 16:34:11
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2083 forum posts
60 photos
Posted by Martin Harris on 24/09/2020 15:41:28:

"Bulbs? Bulbs is wot you plant in your garden" was indelibly knocked into me by our storemen at work

Your storemen should have been sent for a long wait. It is a glass bulb with an incandescent element.

Martin Harris24/09/2020 17:40:00
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9558 forum posts
258 photos

We told apprentices to pop into the stores and ask for a long weight (after explaining how the return weights for switchboard cords came in different sizes of course).

The word bulb probably only appeared in the stores rate book (roots deep in GPO/Civil Service origins) in connection with wet and dry bulb hygrometers.

leccyflyer25/09/2020 07:09:15
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1631 forum posts
339 photos
Posted by Geoff S on 24/09/2020 13:17:11:
Posted by John Lee on 24/09/2020 11:47:49:

Full size related but it just goes to show how interference can be generated from an unexpected source. Ofcom link

That's a very strange light bulb with an ES (Edison Screw) connector. I was involved with selling light bulbs in our family electrical/radio etc shop from childhood in the 1940s onwards and all mains light bulbs were bayonet fittings. Thiis was at a time when many houses had gas rather than electric lighting (and no indoor plumbing) in our small mining town. The only screw fitting bulbs we sold were MES (Miniature Edison Screw) bulbs for torches and bike lamps.

I can only assume there was a loose connection to the filament or perhaps a mechanical connection that wasn't really secure and thus generated a spark. As Bob mentioned early radio transmitters used spark gaps to generate the RF - and that's not so long ago in real terms. I bet it was an interesting investigation and very satisfying to bring it to a successful conclusion.

On the old TV interference I'm guessing it was a valve one with a CRT which needed several kilovolts for the EHT and again the source of the interference was a spark.

Geoff

Lots of the ceiling mounted spotlights have Edison screw fittings these days Geoff, we used to have to carry two sizes for years until we got rid of them.14mm and 27mm IIRC.

ron evans25/09/2020 09:42:11
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465 forum posts
28 photos

A bit off topic, but lightbulb related.

A few days ago the lightbulbs in the dining lit up with a low glow without being switched on.

They switched on & off normally but the low glow remained and fluctuated for a few minutes before going out.

Any explanations out there.

Thanks.

Ron

martin collins 125/09/2020 09:52:15
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461 forum posts
207 photos

Space Aliens laugh

J D 825/09/2020 09:54:01
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1626 forum posts
87 photos

What sort of bulbs were they? If you hold a fluorescent tube under a high power cable it will glow.

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