What causes this - Page 1
Forum section: electronics / general

author: G7PSK
author_rank: Super Contributor
timestamp: September 28, 2020, 08:32:38 pm
content: Most of these vintage style LED bulbs don't use switching droppers so what is causing the RF emissions from them this is not the first time I have heard of the problem but nothing on this level before.https://news.stv.tv/west-central/householders-vintage-lightbulbs-cause-chaos-for-pilots?fbclid=IwAR0tTAnNTT8Ym5_sxuVRWlrlKbEXMNL2_C0-BNP_zN1Y78FGI2qxGUVB53k&top

author: fourfathom
author_rank: Super Contributor
timestamp: September 28, 2020, 08:48:59 pm
content: Many of these "vintage" bulbs are vintage in appearance only. Inside they have LEDs and switchers. These could create interference, but it would have to be very bad to significantly affect distant airplane radio reception. I suppose it's possible though.A true incandescent vintage-style bulb will not generate radio interference.

author: james_s
author_rank: Super Contributor
timestamp: September 28, 2020, 08:53:01 pm
content: Aircraft radio is AM which is far more prone to interference than FM. I'm surprised these bulbs were radiating strongly enough to affect planes in the air, though when listening to the air band on my scanners many different kinds of LED bulbs and other devices do radiate interference that I can easily hear on the radio.

author: G7PSK
author_rank: Super Contributor
timestamp: September 29, 2020, 07:55:44 am
content: There dose not seem to be any switching regulators in these bulbs just a current regulator and rectifier. Big Clive did a tear down.https://youtu.be/NffhdAz9pc4

author: Nusa
author_rank: Super Contributor
timestamp: September 29, 2020, 11:14:06 am
content: The article doesn't really identify the exact technology of the "vintage" light bulb. Perhaps it's not the same implementation that Clive tore down. Perhaps they aren't even LED's?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 29, 2020, 12:43:26 pm
content: Some of my early high power LED house lights are strong enough to cause reception problems. Shown looking at line with a home made LISN, DC-1GHz. The house wiring makes for a good antenna. Some were better than others. I would typically buy one, test it and if it had low emissions, buy several.I'm surprised the FCC would allow the import of these Chinese lights. Then again, I know I shouldn't be.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 29, 2020, 12:51:21 pm
content: They should abolish the power factor requirement for small LED lights, so that there would be one less reason to use a switching power supply in those.

author: richard.cs
author_rank: Super Contributor
timestamp: September 29, 2020, 03:38:52 pm
content: Certainly at least some of that style use switching regulators.Wait, no that is very clearly a filament lamp with real, tungsten, filament. No LEDs there at all. I know what's happening.I have heard about it before with this type:http://www.lamptech.co.uk/Spec%20Sheets/IN%20WC%20D%20Ediswan%20Beautalite.htmbut the long wire filaments of the type in the article are probably vulnerable to it as well. Essentially they are often vacuum filled (particularly as the uncoiled filament would have too much convective loss if they were gas filled) and at certain points in the mains cycle is is energetically favourable for the electrons to jump off the tungsten part-way along and fly through the vacuum down to the other end and hop back on. In doing so various RF oscillations can occur as they get pulled into spiral paths by the local magnetic fields and the radiate RF energy in a magnetron-like way.Read a little about it here, but it seems like a known problem.https://www.emcrules.com/2017/04/can-incandescent-light-bulbs-cause.htmlThat article talks about interference in the FM broadcast band which is immediately adjacent to the air band.

author: fourfathom
author_rank: Super Contributor
timestamp: September 29, 2020, 04:18:30 pm
content: Quote from: richard.cs on September 29, 2020, 03:38:52 pmThank you for posting this. I had no idea!

author: james_s
author_rank: Super Contributor
timestamp: September 29, 2020, 05:51:15 pm
content: Quote from: NiHaoMike on September 29, 2020, 12:51:21 pmIs there a power factor requirement? Either way the LED bulbs that lack switchmode drivers are crap, they flicker at 120Hz which I can't stand. It's not that hard to make a clean switchmode driver, you just have to buy decent quality bulbs.

author: Gyro
author_rank: Super Contributor
timestamp: September 29, 2020, 05:58:08 pm
content: I suspect that a lot of the interference from these lamps comes from the cheap un-snubbed mains bridge rectifiers.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 29, 2020, 10:15:31 pm
content: Quote from: james_s on September 29, 2020, 05:51:15 pmThere is a requirement although I'm not sure exactly when it applies. Making them flicker free is just a matter of using large enough capacitors.

author: richard.cs
author_rank: Super Contributor
timestamp: September 29, 2020, 10:30:35 pm
content: Quote from: NiHaoMike on September 29, 2020, 10:15:31 pmIn the EU there is not a power factor requirement for LED lamps as switch mode supplies under 75 W (apparently it's in EN61000-3-2) are exempted from it.Of course we have established that the RF noise source the OP asked about isnota SMPS at all but something rather more weird.

author: richnormand
author_rank: Unknown
timestamp: September 29, 2020, 10:44:33 pm
content: Quote from: richard.cs on September 29, 2020, 03:38:52 pmSounds like Barkhausen oscillation sometime seen in old tvs? The oscillations could be very high frequencies and leave noise on the image. Since they were generated often by the horizontal drive tube (valve) it would be synchronized with the deflection and thus leave a thick stable vertical line on the screen. They could also be picked up on AM and shortwave radio. You could buy a small magnet clamp to affix to the glass tube and position it to eliminate the effect.

author: james_s
author_rank: Super Contributor
timestamp: September 30, 2020, 07:10:59 am
content: Quote from: NiHaoMike on September 29, 2020, 10:15:31 pmLarge enough capacitors are expensive and bulky, using a switchmode driver allows them to be much smaller. I've never seen a linear LED lamp driver that didn't flicker.