Banana Skins – August 2021 (#347-353)

347. Cellular telephones can interfere with medical equipment – Mayo Clinic concludes

OBJECTIVE: To assess the potential electromagnetic interference (EMI) effects that new or current-generation cellular telephones have on medical devices. 

MATERIAL AND METHODS: For this study, performed at the Mayo Clinic in Rochester, Minn, between March 9, 2004, and April 24, 2004, we tested 16 different medical devices with 6 cellular telephones to assess the potential for EMI. Two of the medical devices were tested with both new and old interface modules. The 6 cellular telephones chosen represent the different cellular technology protocols in use: Code Division Multiple Access (2 models), Global System for Mobile communications, Integrated Digital Enhanced Network, Time Division Multiple Access, and analog. The cellular telephones were tested when operating at or near their maximum power output. The medical devices, connected to clinical simulators during testing, were monitored by observing the device displays and alarms. 

RESULTS: Of 510 tests performed, the incidence of clinically important interference was 1.2%; EMI was Induced in 108 tests (21.2%). Interference occurred in 7 (44%) of the 16 devices tested.

CONCLUSIONS: Cellular telephones can interfere with medical equipment. Technology changes in both cellular telephones and medical equipment may continue to mitigate or may worsen clinically relevant interference. Compared with cellular telephones tested in previous studies, those currently in use must be closer to medical devices before any interference is noticed. However, periodic testing of cellular telephones to determine their effects on medical equipment will be required.

(Taken from: “Cellular telephone interference with medical equipment” by Tri JL, Severson RP, Firl AR, Hayes DL, Abenstein JP. Division of Foundation Telecommunications and Network Services, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. 29 Oct 05, Mayo Clin Proc. 2005 Oct;80(10):1286-90, received via: Interference Technology eNews Oct 27 2005.)

348. Five interference anecdotes from Tim Haynes

Radar-controlled gun on board a refitted warship. VHF transmissions would make the gun guidance go wild, pointing it into the superstructure etc. Lucky it wasn’t loaded.

My own experience. Radio ham, transmitting on a UHF channel 433.325MHz hears own voice on a VHF transceiver, which was not normal. Received voice comes and goes with the movement of traffic. By watching the cars around, determines that it only occurs when a particular car is nearby – a Fiat Coupé. I ran this on EMC-PSTC when it happened and got Ferrari and Fiat writing to me wanting to know if it was their vehicle causing the problem. This was probably RF and switching causing the problem in the ECU of the Fiat.

Dual technology (IR and microwave) movement detectors used to control the lights in (a house / an office) would also detect radio transmission from passing cars using VHF radio. Soon the lights were going on and off like Xmas tree lights as all taxi, fire, police, ambulance drivers “blipped” their transmitters on passing.

Radio ham sitting in Tesco’s car park waiting for wife to arrive with shopping. Talking on local UHF ham repeater. Man comes to his BMW7 series and with a flourish “blips” the remote unlock. Nothing happens. Another flourish. Still nothing. Walks around the car – checks number plate – yes it is his. Another flourish – nothing. Radio ham stops transmitting and leans out of the car window say “it will work now”. Aggravated flourish! car unlocks and owner starts to load shopping. 

Ham goes back to transmitting. Owner shoves shopping trolley into empty parking bay and gets into car. After two to three minutes, owner gets out of car and checks all doors are shut and gets back in. Gets out again and looks pitiful. Radio ham stops transmitting, leans out of window and say “ it will start now!”. Owner looks puzzled, gets into car and starts it first time, drives off at speed. Radio ham gets out of his old, non-electronic, car and paints another circle with black and blue quadrants in it on the front wing. Pulls flaps down on flying helmet and returns to reminiscing about days as fighter pilot. (This one is part true and part poetic license – you can decide which parts are which!)

(A collection of anecdotes sent in on 10th November 2005 by Tim Haynes.)

349. New Pentagon system suspected of interfering with garage door openers

A widespread problem with a mysterious radio signal that caused some garage doors in the Ottawa region to stop working has vanished. The powerful radio signal causing the problem stopped transmitting on Thursday afternoon, around the time CBC News contacted the U.S. Embassy to ask if it knew anything about it. The embassy denies that it had anything to do with it. 

The signal was being transmitted at 390 megahertz, a frequency used by the Pentagon’s new Land Mobile Radio System. The same frequency is used by garage doors openers, which started to malfunction around the city about two weeks ago. A similar problem has popped up around military bases in the States. 

The world’s biggest garage door manufacturer, the Chamberlain group, took the problem seriously enough to fly design engineer Rob Keller to Ottawa from its Chicago headquarters, with machinery to try to track the signal. But by the time he got there, the signal was gone.

(Sent in by Doug Milligan, Senior Control Engineer, JNUP, who found it on CBC News “Garage doors work after mysterious radio signal disappears,” Mon, 07 Nov 2005 13:01:24 EST.)

350. Mobile phone ban continues on flights

The ban on the use of mobile phones by passengers on planes is set to continue. New tests by the Civil Aviation Authority confirmed that phones are still a threat to aircraft. The latest study found that the use of mobile telephones can adversely affect navigation and communication functions, producing significant errors on instrument displays and background noise on audio outputs. The CAA study recommended that as well as the usual on-board warnings about the use of mobiles, there should also be reminder notices in airport departure lounges and warnings by check-in staff. 

The research backs up reports from pilots, who have stated that interference from mobiles has caused: false notification of unsafe conditions – for example, incorrect baggage compartment smoke alarm warnings; malfunction of aircraft systems; interrupted communications due to noise in the flight crew headphones; distraction of crews from their normal duties due to increased work levels and the possibility of having to invoke emergency drills.

Dan Hawkes, an avionics specialist at the CAA who supervised the research, said: “The tests demonstrate that mobile telephone use near an aircraft’s flight deck or avionics equipment bay can adversely affect systems that are essential for safe flight. “For safety reasons the current policy of prohibiting the use of mobile telephones by passengers while the aircraft’s doors are closed for flight must continue.” 

(Copyright (c) Press Association Ltd 2003, All Rights Reserved. 06/05/2003 13:31)

351. TETRA radio system interferes with amateur radio

The roll-out of Tetra (Airwave) in Manchester is making itself known. I travel down the M60 between the A627M to the west of Bury, 2 or 3 times a week. I travel back and forth to work 5 days a week using the same route. I’ve used the same Amateur Radio transceiver (Kenwood) in my car for the last 5 years. What has changed? At various locations on the M60 and in Oldham, Ashton and Stalybridge, the 430MHz band is unusable for a number of miles on certain roads. The only way to get rid of the damn digital out of band carrier noise, is to switch on the ctcss (continuous tone coded squelch system), probably the equivalent on switching the fog lamps on! We are finding that increasingly it is necessary to take this course of action, or listen to the noise for the next few miles. 

(Sent in by Graham Eckersall of Barcrest, on 10th Feberuary 2003.)

352. Enhanced immunity testing required to overcome telecom failures

The International Telecommunications Union publishes the ITU-T Recommendations, which include the “K Series” of recommendations on the resistability (EMC immunity) of telephone-related equipment. Recently (Nov 2004) an amendment was published to its Recommendation K.20, which covers equipment installed in telecommunications centres. It seems that despite passing the very thorough and quite tough immunity tests in K.20, including the ‘enhanced levels’, a new design of line card installed in 1999-2000 suffered a large number of IC failures by 2002. Three years of intensive study resulted in a new test that reproduced the type of damage seen, and cards that have been modified to pass this new test seems to be much more reliable as a result.

The new test involves applying a voltage at the AC power frequency between two external ports (connectors for external telecommunication cables). The generator is ‘floating’ – not connected to the earth of the equipment under test as in the usual K.20 tests. Coupling resistors of between 100 and 200 ohms are used, and the voltage applied for periods of around one-third of a second. The voltage is increased gradually from low levels, until it exceeds the voltage at which the secondary protection devices in the equipment operate. In the case of the failing line cards above, the damage was replicated with coupling resistors of 140 ohms and a voltage of 145V rms.

(Taken from: ITU-T Recommendation K.20, “Resistibility of telecommunication equipment installed in a telecommunications centre to overvoltages and overcurrents” Amendment 1, November 2004, “Floating transverse power induction and earth potential rise test for ports connected to external symmetric pair cables”. For manufacturers of equipment that could be connected to long signal, data or control cables, especially if those cables exit a building, applying the relevant K series immunity tests should help improve reliability. Some of them are similar to IEC 61000-4 series tests, but some are very different and/or much tougher.) 

353. Digital box interference riggers ‘SOS’ alert and helicopter search

A faulty TV digital box sparked a rescue mission from RAF Kinloss by sending out a signal identical to those transmitted by vessels in distress. The Kinloss site in Moray, which co-ordinates rescue operations across the UK, detected an “SOS” call from the Portsmouth area on 5 January. 

A coastguard helicopter spent two hours searching the harbour area before the signal was traced to dry land. An RAF spokesman said the signal had been a “complete freak”. Telecoms regulator Ofcom was asked to look into the signal and confirmed the source. 

RAF spokesman Michael Mulford said the Aeronautical Rescue Co-ordination Centre at the airbase had picked up the beacon from one of five orbiting satellites. He said it was transmitting on the major emergency frequency. “We traced it to Portsmouth Harbour, checked and found out there were no vessels in the area or missing planes.” The rescue centre then contacted Ofcom, which was able to establish it was coming from a household. 

“Digital boxes shouldn’t be sending out signals, let alone maydays” Ofcom spokesman Mr Mulford added: “This is very very unusual, it’s a complete freak and the odds of a digibox sending out such a signal must be astronomical. “The guy who owns it really should do the lottery because the chances of sending out a signal from a digibox and sending out precisely and exactly on a major emergency channel are far more than 14 million to one.” 

Ofcom has since removed the £50 Freeview box for tests. An Ofcom spokesman said: “This is a real one-off as digital boxes only receive signals. “They shouldn’t be sending out signals, let alone maydays. The householder was happy to hand it over to our engineers who are trying to get to the bottom of the defect.” 

(Taken from BBC News / Scotland, Sunday, 15 January 2006, 13:03 GMT. This was sent in by both Graham Eckersall of Barcrest and by Alex McKay of Technology International (Europe) Limited, who got it from Claire Ashman of RFI.) 

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.

About The Author

Keith Armstrong

After working as an electronic designer, then project manager and design department manager, Keith started Cherry Clough Consultants in 1990 to help companies reduce financial risks and project timescales through the use of proven good EMC engineering practices. Over the last 20 years, Keith has presented many papers, demonstrations, and training courses on good EMC engineering techniques and on EMC for Functional Safety, worldwide, and also written very many articles on these topics. He chairs the IET’s Working Group on EMC for Functional Safety, and is the UK Government’s appointed expert to the IEC committees working on 61000-1-2 (EMC & Functional Safety), 60601-1-2 (EMC for Medical Devices), and 61000-6-7 (Generic standard on EMC & Functional Safety).

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