Squirrel Cage (Filament?) Lamps interfere with aircraft radio on approach! - Page 1
Forum section: electronics / general

author: Gyro
author_rank: Super Contributor
timestamp: December 05, 2020, 02:23:02 pm
content: I saw this story on the BBC news site yesterday but can't find it now...Apparently commercial aircraft have been suffering radio blackouts in a localised area at 6000-10000ft on approach to Glasgow (UK) airport. Tracing the flight data back, they managed to track the blackouts back to a particular location and reported it to Ofcom for investigation.Ofcom sent out their trackers, who finally narrowed the interference down to some unsuspecting homeowner who had bought a few 'squirrel cage' style LED filament bulbs from one of the usual culprits! Apparently the squirrel cage format formed an efficient enough antenna at the (I think) 118 and 122MHz commercial aircraft comms bands to pump out enough power a vertical pattern to block them out while the aircraft on approach were still at significant altitude. Presumably the noise source was something like broadband rectifier switching noise!The potential implications for widespread broadcast interference from large numbers of these imported 'cheapies' are pretty horrible.Here's the relevant Ofcom page...https://www.ofcom.org.uk/about-ofcom/latest/features-and-news/interference-issueThe BBC story made reference to a discovery, many years ago, of the same antenna effect with squirrel cage format incandescent filament lamps. Presumably radiating some external noise source, but I can't remember the details.EDIT: From the photo on the Ofcom site, it's possible that theywereactually incandescent filament ones - I don't know now!

author: Zero999
author_rank: Super Contributor
timestamp: December 05, 2020, 05:54:52 pm
content: The photograph in the article appears to be a standard incandescent lamp. I'm glad Ofcom are going after the sellers, rather than the home owner, who I hope managed to get a refund.

author: Gyro
author_rank: Super Contributor
timestamp: December 05, 2020, 06:35:37 pm
content: Yes, it seemed intuitive that they would be LED, given the EMC emissions of cheap lamps. I'm not sure how likely it would be for incandescent lamps to bethatefficient an antenna for mains bourne interference. I'm pretty sure the BBC article said LED, they probably gathered more detail from Ofcom.Either way, it looks like a pretty good antenna design!EDIT:Hmm, the plot thickens...https://www.emcrules.com/2017/04/can-incandescent-light-bulbs-cause.htmlhttp://www.redca.eu/EUANB%20Documents/EUANB%20TGN%2035%20Guidance%20on%20the%20benign%20character%20of%20filament%20%20lamps%20May%202017.pdfhttp://bulbcollector.com/forum/index.php?topic=1101.0Thread title changed.

author: bd139
author_rank: Super Contributor
timestamp: December 05, 2020, 07:07:33 pm
content: That was a rather interesting rabbit hole. Thanks for posting.Wonder if that explains the shitty 2m noise around here in evenings. Not that I have a radio around any more.

author: CJay
author_rank: Super Contributor
timestamp: December 05, 2020, 09:14:03 pm
content: Was discussed at some length on the RSGB tech or workshop mailing list I think, I wonder if the real problem was a crappy dimmer and the lamp was just an efficient radiator...

author: floobydust
author_rank: Super Contributor
timestamp: December 05, 2020, 09:40:29 pm
content: A very long time ago, popular knowledge incandescent traffic lights would always trigger an X-band radar detector, as if the bulbs emit a 10GHz chirp when switching. Not sure if it was the red off or green on, but a car radar detector would always chirp at the light change.

author: james_s
author_rank: Super Contributor
timestamp: December 06, 2020, 04:39:24 am
content: Quote from: floobydust on December 05, 2020, 09:40:29 pmI'd never heard of that, I wonder what the cause was? The lamps used in all three colors are identical, and at least in North America they were gas filled C filament lamps since at least the 1950s, I don't know exactly when the standard traffic signal lamps were developed.

author: bdunham7
author_rank: Super Contributor
timestamp: December 06, 2020, 05:10:22 am
content: [quote from link]"squirrel-cage lamps operating above 160 volts. The interference happens only above that voltage threshhold and cannot be duplicated with 110-volt lamps"Finally--proof positive of the superiority of the 120/240 American electrical system!

author: coppercone2
author_rank: Super Contributor
timestamp: December 06, 2020, 05:21:56 am
content: treez?

author: floobydust
author_rank: Super Contributor
timestamp: December 06, 2020, 06:35:00 am
content: Quote from: james_s on December 06, 2020, 04:39:24 amMains freq. wiring and incandescent bulbs with polished metal reflectors - who knows what the RF properties are. As a parabolic dish with a metal filament at the focal point, I could see it transmitting RF. Whether it's triacs or mechanical switches, I have no idea what the oscillator was when a lamp turned on.I was constantly baffled that a microwave pulse was being generated and emitted by traffic lights, but it happened with many radar detectors and other drivers said it was common nuisance alarm.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 06, 2020, 12:42:28 pm
content: Most likely something simple like the switching relay acting as a spark gap transmitter.