Silicon ChipTechno Talk - January 2021 SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Subscriptions: PE Subscription
  4. Subscriptions: PicoLog Cloud
  5. Back Issues: PICOLOG
  6. Publisher's Letter
  7. Feature: The Fox Report by Barry Fox
  8. Feature: Techno Talk by Mark Nelson
  9. Feature: Net Work by Alan Winstanley
  10. Project: Nutube by John Clarke miniature valve stereo preamplifier by John Clarke
  11. Project: Complete Arduino DCC Controller by Tim Blythman
  12. Project: Using Cheap Asian Electronic Modules by Jim Rowe
  13. Feature: KickStart by Mike Tooley
  14. Feature: PICn’Mix by Mike Hibbett
  15. Feature: AUDIO OUT by Jake Rothman
  16. Feature: Make it with Micromite by Phil Boyce
  17. Feature: Interference and noise by Ian Bell
  18. Feature: Max’s Cool Beans by Max the Magnificent
  19. Feature: Visual programming with XOD by Julian Edgar
  20. Advertising Index: Max’s Cool Beans by Max the Magnificent
  21. PCB Order Form

This is only a preview of the January 2021 issue of Practical Electronics.

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Articles in this series:
  • (November 2020)
  • (November 2020)
  • Techno Talk (December 2020)
  • Techno Talk (December 2020)
  • Techno Talk (January 2021)
  • Techno Talk (January 2021)
  • Techno Talk (February 2021)
  • Techno Talk (February 2021)
  • Techno Talk (March 2021)
  • Techno Talk (March 2021)
  • Techno Talk (April 2021)
  • Techno Talk (April 2021)
  • Techno Talk (May 2021)
  • Techno Talk (May 2021)
  • Techno Talk (June 2021)
  • Techno Talk (June 2021)
  • Techno Talk (July 2021)
  • Techno Talk (July 2021)
  • Techno Talk (August 2021)
  • Techno Talk (August 2021)
  • Techno Talk (September 2021)
  • Techno Talk (September 2021)
  • Techno Talk (October 2021)
  • Techno Talk (October 2021)
  • Techno Talk (November 2021)
  • Techno Talk (November 2021)
  • Techno Talk (December 2021)
  • Techno Talk (December 2021)
  • Communing with nature (January 2022)
  • Communing with nature (January 2022)
  • Should we be worried? (February 2022)
  • Should we be worried? (February 2022)
  • How resilient is your lifeline? (March 2022)
  • How resilient is your lifeline? (March 2022)
  • Go eco, get ethical! (April 2022)
  • Go eco, get ethical! (April 2022)
  • From nano to bio (May 2022)
  • From nano to bio (May 2022)
  • Positivity follows the gloom (June 2022)
  • Positivity follows the gloom (June 2022)
  • Mixed menu (July 2022)
  • Mixed menu (July 2022)
  • Time for a total rethink? (August 2022)
  • Time for a total rethink? (August 2022)
  • What’s in a name? (September 2022)
  • What’s in a name? (September 2022)
  • Forget leaves on the line! (October 2022)
  • Forget leaves on the line! (October 2022)
  • Giant Boost for Batteries (December 2022)
  • Giant Boost for Batteries (December 2022)
  • Raudive Voices Revisited (January 2023)
  • Raudive Voices Revisited (January 2023)
  • A thousand words (February 2023)
  • A thousand words (February 2023)
  • It’s handover time (March 2023)
  • It’s handover time (March 2023)
  • AI, Robots, Horticulture and Agriculture (April 2023)
  • AI, Robots, Horticulture and Agriculture (April 2023)
  • Prophecy can be perplexing (May 2023)
  • Prophecy can be perplexing (May 2023)
  • Technology comes in different shapes and sizes (June 2023)
  • Technology comes in different shapes and sizes (June 2023)
  • AI and robots – what could possibly go wrong? (July 2023)
  • AI and robots – what could possibly go wrong? (July 2023)
  • How long until we’re all out of work? (August 2023)
  • How long until we’re all out of work? (August 2023)
  • We both have truths, are mine the same as yours? (September 2023)
  • We both have truths, are mine the same as yours? (September 2023)
  • Holy Spheres, Batman! (October 2023)
  • Holy Spheres, Batman! (October 2023)
  • Where’s my pneumatic car? (November 2023)
  • Where’s my pneumatic car? (November 2023)
  • Good grief! (December 2023)
  • Good grief! (December 2023)
  • Cheeky chiplets (January 2024)
  • Cheeky chiplets (January 2024)
  • Cheeky chiplets (February 2024)
  • Cheeky chiplets (February 2024)
  • The Wibbly-Wobbly World of Quantum (March 2024)
  • The Wibbly-Wobbly World of Quantum (March 2024)
  • Techno Talk - Wait! What? Really? (April 2024)
  • Techno Talk - Wait! What? Really? (April 2024)
  • Techno Talk - One step closer to a dystopian abyss? (May 2024)
  • Techno Talk - One step closer to a dystopian abyss? (May 2024)
  • Techno Talk - Program that! (June 2024)
  • Techno Talk - Program that! (June 2024)
  • Techno Talk (July 2024)
  • Techno Talk (July 2024)
  • Techno Talk - That makes so much sense! (August 2024)
  • Techno Talk - That makes so much sense! (August 2024)
  • Techno Talk - I don’t want to be a Norbert... (September 2024)
  • Techno Talk - I don’t want to be a Norbert... (September 2024)
  • Techno Talk - Sticking the landing (October 2024)
  • Techno Talk - Sticking the landing (October 2024)
  • Techno Talk (November 2024)
  • Techno Talk (November 2024)
  • Techno Talk (December 2024)
  • Techno Talk (December 2024)
  • Techno Talk (January 2025)
  • Techno Talk (January 2025)
  • Techno Talk (February 2025)
  • Techno Talk (February 2025)
  • Techno Talk (March 2025)
  • Techno Talk (March 2025)
  • Techno Talk (April 2025)
  • Techno Talk (April 2025)
  • Techno Talk (May 2025)
  • Techno Talk (May 2025)
  • Techno Talk (June 2025)
  • Techno Talk (June 2025)
Bad boy bulbs Techno Talk Mark Nelson Unwelcome interference is again our topic this month, but on a different kick. This time, the investigation team performed splendidly, tracking down a hapless householder who was jeopardising the safety of the 8.85 million passengers who use Glasgow airport each year. T his month’s EMR nightmare starts with the oldest, and you’d think humblest of electrical items – the lightbulb. Someone unwittingly bought some light bulbs that should never have been put on sale in the first place, and which had defects that were recognised 70 years ago. Mission impossible? Pilots flying aircraft in and out of Glasgow airport complained they were suffering radio blackouts when they were between 6,000 and 10,000 feet in the air. Voice communication between aircrew and the controllers on the ground was wiped out by mystery interference, meaning crews were unable to hear vital air traffic control messages. Locating and identifying the source of the jamming signal aloft was well-nigh impossible on account of the height of the aircraft and their flying speed. Finding the source was a veritable needle-in-a-haystack puzzle, but OFCOM’s investigators were not easily deterred. An ‘area of probability’ was narrowed down by using flight-tracking software to correlate the location of planes reporting the issue with the corresponding location on the ground. With this done, the quest turned into a ground-level investigation centred on a single town. This task involved using receivers aboard vehicles and driving through the suspected area until the interference was heard. Old-fashioned footwork Having pinned down the area where the signal was strongest, the investigators then used handheld equipment to cover the remainder of the search area on foot. The team visited a number of likely properties and they eventually located the source. But what was jamming the sensitive aircraft radios so effectively? If you’re a regular reader of this column (and if not, why not?), you may well be screaming: ‘Oh no, it’s those blessed LED light bulbs that hoot from DC to daylight’, but you’d be wrong. In fact, the culprits were squirrels – or rather their cages. Let me explain, albeit in a roundabout way. 10 The problem with squirrels First, let’s recall a very apposite statement made in 1905 by the philosopher George Santayana in his book, The Life of Reason. It read, ‘Those who cannot remember the past are condemned to repeat it.’ The radio jamming at Glasgow airport proves his point perfectly. Back in 1905, the incandescent lamp bulb was not particularly efficient and to counter this, manufacturers were doing their damnedest to squeeze the maximum amount of light from a glowing filament. One technique involved threading the wire filament up and down the length of the bulb multiple times in a circular fashion using a system of hooks and frames until it resembled a squirrel cage. In those days, keeping pet squirrels in cages was not uncommon, although nowadays it’s considered pretty cruel by most people. After the sale of most incandescent bulbs was phased out by European legislation, lamp manufacturers discovered a loophole that allowed them to sell ‘decorative’ incandescent lamps, and the squirrel cage bulb has returned. These are usually made of tinted glass and have the word ‘rustic’ in their description; for example: https://amzn.to/32C1BTL Get to the point! OK, so what’s the connection between radio jamming and Santayana? Precisely this – OFCOM’s photo of the errant lamp bulb that was wiping out air traffic control frequencies (118 to 121MHz, remember this!) showed it was a squirrel cage ‘deco’ bulb. Electromagnetic radiation does not occur with modern incandescent bulbs that use short, coiled filaments, but the multiple straight wires used in squirrel cage lamps radiate like mad and can affect FM radio transmissions (88 to 108MHz) and the nearby air band (118 to 121MHz). The mechanism is so deeply technical that I cannot paraphrase it in a sentence, but you can read about it here: https://bit.ly/pe-jan21-fm Back in the early 1950s this potential for harmful interference was already recognised in America, where power companies were changing out straight-filament bulbs for consumers (read Popular Science magazine, April 1953, https://bit.ly/pejan21-ps). Nobody cares today, though, because those who do not remember the past are condemned to repeat it. Happy ending? OFCOM confirms that the interference at Glasgow was caused by four ‘vintage’ lightbulbs that the homeowner had recently bought online (not necessarily the ones mentioned above). The house was directly underneath the flightpath of the aircraft and so every time a plane passed and the lamps were in use, the air crew suffered the interference. The bulbs were replaced with non-interfering types and checks with National Air Traffic Services and aircraft operators confirm that the area is now free of interference. OFCOM’s spectrum enforcement team is following up the case with the lightbulb suppliers, to make sure no more dangerous bulbs are sold to unwitting customers. Tracking down the disturbance that was not merely annoying but positively life-threatening was a highly impressive effort. This work, by telecoms regulator OFCOM, confers great credit on their spectrum assurance team, who found the unknowing culprit. So that’s all right then? Hardly. Squirrel cage lamp bulbs are still sold widely; as I write this article, eBay has 1,284 offers of them for sale, while Amazon has more than 2,000. All manner of other online sellers and out-of-town DIY sheds sell them as well. How many of those bulbs have been tested for EMC compatibility? Manufacturers – and UK distributors – are responsible for exercising due diligence regarding the CE marking they place on their products, but how many of them are aware of their legal responsibilities for public safety? And what if they are made on the other side of the world, where CE merely signifies ‘Chinese export’? Local trading standards authorities are responsible for enforcing regulations, but they may not be aware of non-conformant merchandise. So, as always – caveat emptor – let the buyer beware! Practical Electronics | January | 2021