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Banana Skins – May 2022 (#378-382)

378. Mobile phones can interfere with aircraft systems

Navigation and control instruments can be caused to malfunction. During the approach of an Alitalia aircraft at Turin airport on 31 December, 1995, one of the 160 passengers onboard switched on his mobile phone, thus blocking the plane’s autopilot system. There was also interference with the pilot’s contact with the control tower.

The conditions were dense fog. The pilot realized what had happened and, displaying a cool nerve, was able to take manual control of the aircraft and land it without further incident. (Source: TT 960103).

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A Dash of Maxwell’s: A Maxwell’s Equations Primer – Part Two

Maxwell’s Equations are eloquently simple yet excruciatingly complex. Their first statement by James Clerk Maxwell in 1864 heralded the beginning of the age of radio and, one could argue, the age of modern electronics.

(Taken from “Application Areas for MobilePhoneGuardTM”.)

379. TVs susceptible to the frequency and type of RF modulation

The annex to IEC 61000-4-3 explains that it was decided to use amplitude modulation (of the radiated RF test signal) and not pulse (digital) modulation as the differences were small. However, when testing televisions for immunity to GSM mobile services, the use of a 200Hz modulation was disastrous, and was only solved by using the correct 186Hz signal. 

The problem arose because 200Hz was a harmonic of the television frame frequency (which is 50Hz in the EU – Editor). This points to the criticality of such tests, which when viewed in the wider context highlights the impracticability of simulating all digital services during RF immunity testing. So should we be looking at a new approach for RF immunity testing?

(Taken from: “Standards – are we getting what we need” by Peter Kerry, President of CISPR, EMC-UK 05, Newbury, 11-12 October 2005, pages 49‑51 in the conference record.)

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380. Hunting Radio Howlers – Government Vans on the Track (historical)

The wireless oscillators do not have it all their own way. Re-radiated howls which spoil reception for other listeners are to be tracked down by Government experts employing the latest methods. By the end of this month, the first of the new direction-finding motor-vans will, it is expected, be delivered to the Post Office engineers who are specially concerned with stamping out oscillation. These vans will do their best to work in couples. 

The general idea is to listen to any notable howls on frame aerials. A compass bearing is taken of the quarry and the aerial is swung round until the sound reaches a minimum. This gives a still closer reading. Next, the van moves on to another spot and the procedure is repeated. The bearing, naturally, is changed (just as a lamp-post changes it’s apparent position as you walk past it). 

Finding the ‘Lair’: When the bearings are plotted out on an ordnance map of the district, you will get two or more lines cutting each other and the spot where they intersect marks the ‘lair’ of the oscillator, or thereabouts, for an aerial is a length of wire which does not give a very exact ‘fix’ for this form of land navigation. Two vans, in wireless telephonic touch with each other on a wavelength that does not interfere with broadcasting, can conduct a hunt in quite a short time and the offending listener is eventually run to earth.

(Just to prove that EMI is nothing new, the above item is from the Daily Mail, 21 April 1926, reprinted in Automotive EMC Newsletter 4th June 2006. The problem described was caused by the local oscillators in early ‘superhet’ radio sets, which could be re-radiated from the antenna or mains wiring and cause interference.) 

381. Airport transmissions interfere with some cars on nearby motorway (1)

While towing a caravan south between junctions 24 and 23 of the M1 recently, the turbo of my 29,000 mile Audi A4 TDI suddenly shut down. There were no warning lights or mechanical noises, simply a serious loss of power. I struggled off the motorway and a mobile technician from Audi Assist checked the car the following day. He ran a series of electronic checks but could find no fault other than a “possible” mechanical turbo failure. On the subsequent test run, the turbo was working again and In have completed a further 200 miles without incident. Could the problem have been due to the electronic interference that has previously been mentioned in your column? A.S., Doncaster.

‘Honest John’ replies: Another reader puts it down to the automatic aircraft landing system at East Midlands Airport. It transmits to planes coming in across the M1 and can apparently interfere with badly shielded car electronics.

(From “South Shields” in the Expert Advice section of the Motoring section of the Daily Telegraph, Saturday August 19, 2006, page 9.)

382. Airport transmissions interfere with some cars on nearby motorway (2)

For many years, automakers have performed electromagnetic compatibility testing of automobiles before their release to consumers. However, as the electronics content of vehicles becomes greater every year, it expands the potential for component or system failure caused by external sources of electromagnetic radiation.

One challenge has come from commercial and military airport radar systems that operate at frequencies from 1.2 to 1.4GHz and 2.7 to 3.1GHz. Cases have been reported in which vehicles near airports and military bases suffered degradation or even failure of critical vehicle systems including braking controls and airbag deployment. As a result, Ford Motor Company and General Motors Worldwide (GMW) have introduced sections in their immunity standards for component testing when exposed to radar pulses, such as those at the 600V/m level.

(Taken from “Required Amplifier Power in Automotive Radar Pulse Measurements” by K. Gove, H-P. Bauer and V. Rodriguez-Pereyra, Evaluation Engineering, August 2006.) 

The regular “Banana Skins” column was published in the EMC Journal, starting in January 1998. Alan E. Hutley, a prominent member of the electronics community, distinguished publisher of the EMC Journal, founder of the EMCIA EMC Industry Association and the EMCUK Exhibition & Conference, has graciously given his permission for In Compliance to republish this reader-favorite column. The Banana Skin columns were compiled by Keith Armstrong, of Cherry Clough Consultants Ltd, from items he found in various publications, and anecdotes and links sent in by the many fans of the column. All of the EMC Journal columns are available at:, indexed both by application and type of EM disturbance, and new ones have recently begun being added. Keith has also given his permission for these stories to be shared through In Compliance as a service to the worldwide EMC community. We are proud to carry on the tradition of sharing Banana Skins for the purpose of promoting education for EMI/EMC engineers.

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