Editor’s Note: We regularly receive requests from readers to publish stories about real EMI/EMC problems faced by real engineers. We are pleased to bring you Banana Skins, a monthly column in In Compliance, and a 20‑year tradition that began in the pages of the EMC Journal. We hope you enjoy the column and look forward to continuing the tradition of sharing these valuable stories.
106. 1998 Grand Prix suffered interference
In the lead-up to the 1998 Grand Prix, electrical storms caused a spike in the power supply which sent major ripples across the facility’s feed lines – crashing all race control computers. After the ensuing chaos, the problem was rectified and the race proceeded as scheduled but the experience left the Silverstone management adamant that this type of disturbance would not be repeated at future events.
(From “Grand Prix UPS weathers the storms”, Electrical Products September 2000 page 34, Electrical Products & Applications: www.imlgrouponthenet.net.)
107. Twinkling antennas cause high levels of emissions
‘Twinkling antennas’ are a recent innovation in the mobile phone market. They incorporate one or more Light Emitting Diodes (LEDs), which are intended to illuminate when the mobile phone is transmitting. Reports from Mobile Phone companies using the 1800 MHz band have highlighted cases of interference from 900 MHz GSM mobiles. It has been suggested that the non-linear characteristics of the LEDs will cause a transmitting twinkling antenna to radiate harmonics.
(Tests carried out by the Radiocommunications agency on two 900 MHz cellphones fitted with twinkling antennas showed that…..) the ERP of the second harmonic…..exceeded the ETS 300 577 maximum.
(From EMC Matters, published by Brian Jones: emc@brianjones.co.uk. The full report of Project 564 and many other interesting documents may be found by hunting around the (legacy) Radiocommunication Agency’s website hosted on Ofcom’s site at: www.ofcom.org.uk/static/archive/ra/rahome.htm.)
108. Industrial microwave oven interferes with cell phone base station
In the UK 886 to 906MHz has been allocated as a band suitable for the operation of Industrial Scientific and Medical (ISM) equipment. ISM machines are at present allowed to emit 120dBμV/m (i.e. 1Volt/metre) measured at 30 metres from the wall of the building housing the equipment over this frequency range. This presents a problem as it occupies part of the band allocated to mobile phone operators.
The main users of the ISM band are organisations operating industrial microwave ovens. The ovens are used in food production although other uses such as vulcanising rubber are also on record. High power magnetrons are used as the source of microwave energy, the magnetrons are designed to operate at 896MHz. For process purposes the ovens are normally conveyor fed.
Consequently depending on the size of product being treated a large aperture exists at each end of the oven allowing relatively high levels of microwave energy to be emitted. The channel 30 mobile to base-station frequency coincides with the magnetron centre frequency. ……. The second oven at Griffith laboratories is of particular interest as the emissions are known to disturb the operation of a base station located in the vicinity.
(Extracted from: “Industrial Microwave Oven (ISM) Emissions and Mitigation Techniques”, Dr D Welsh, Proceedings of EMC York 2000, 10-11 July 2000, www.yorkemc.co.uk.)
109. Australian telco has problems with inadequate immunity to EMI
The current Australian regime (for EMC compliance) only covers emissions requirements, but there has been extensive discussion about whether immunity should also be made mandatory. …..a submission from a major telecommunications network company (Telstra) outlined difficulties it has experienced in dealing with customer equipment susceptible to interference.
The ACA mandates interoperability, safety, and emissions standards but telecoms carriers have little control over the EMC quality of equipment connected to their network.
(From Chris Zombolas of EMC Technologies Pty Ltd: “Australian framework comes under review”, Approval, Sep/Oct 2000 pp 7-8.)
110. EMI problems with early electronic ABS
When Ford began the development of an electronic anti-lock braking system in 1982, their engineers noted certain “concerns” about its behaviour when subjected to high levels of interference. (Ed: Such as those created by mobile radio transmitters of around 100W, either on-board or mounted on nearby vehicles.) Not only was it liable to fail, bad enough if a driver had come to rely on it, but it could do so in a particularly nasty manner, deactivating the system.
(Tom Shelley: “Screening protects anti-skid brakes”, Eureka May 1987, pp 36-37, www.eurekamagazine.co.uk.)
111. High field strengths near vehicles’ on-board transmitters
Fields in and around vehicles with onboard transmitters (at the maximum legal power of 110W) range mostly between 10 and 300 V/m, with some exceptions. Field strengths in and around vehicles adjacent to vehicles with transmitters range mostly between 5 and 100 V/m.
(From “How does EMI affect automotive electronics?” Microwaves, April 1980, pp 96, www.mwrf.com.)
112. Mobile phone use not recommended on aircraft
I’m tempted to think your article about mobile phones on aeroplanes was itself a flight from reality (19 August, p 18). The problem with cellphones is that they radiate at moderate powers which are capable of upsetting the operation of any of the semiconductors in any of the electronic systems in the aircraft.
Try this little experiment: phone a friend using your POT (plain old telephone landline) and then phone someone else using your cellphone. Hold the cellphone at various distances from the POT handset and its cables and see how far away it has to be before you can’t hear the “blippety-blip” noises on the POT. According to the reported statements in the article, the possibility of interference in these little experiments would be “very low” when in fact it almost always occurs.
(Keith Armstrong: “Mobile menace”, letters, New Scientist, 9 September 2000, www.newscientist.com.)
113. Mobile phones cause interference on the flight deck
As a captain of a brand new Boeing 737 aircraft, I can assure readers that the effects of mobile phones are very noticeable on the flightdeck. The chief problem is a series of rapid beeps from the handset when it “checks in” with a base-station. The handset does not need to be making or finishing a call to perform this function, it only needs to be switched on. The interference manifests itself as a loud and annoying interference, but since some of our navigation equipment works on the same frequencies, interference with navigational capabilities cannot be ruled out.
Another more worrying source of cellphone interference was not even mentioned in your report – mobile phones in air-traffic control centres. We had a case the other week on a Spanish sector where a mobile phone in the air-traffic control centre was continuously trying to check in with its base station and the interference was totally blocking the frequency.
Mobile telephones are an airborne menace, but you have to ask why aircraft systems are not better protected against interference in the first place. Thunderstorms can saturate our old-fashioned (but new) AM radios with static, and the ADF navigation equipment will direct the aircraft straight towards the nearest thunderstorm instead of the airfield. Is this really the high-tech field of aviation?
(Ralph Ellis: “Mobile menace”, letters, New Scientist, 9 September 2000, www.newscientist.com.)
114. HV transmission lines cause shock hazards for nearby swimming pools
In general, an above ground pool is 6 to 12 times more hazardous than an in ground pool. Of the cases investigated, the majority of hazardous situations associated with pools were found to be above ground pools in close proximity to transmission line towers. It was recommended that all pools of the above ground type in close proximity to transmission lines be removed immediately.
(D.J.Woodhouse, K.D Newland, W.D. Carman, all from Energy Australia: “Development of a risk management policy for transmission line easements”, ERA’s Earthing 2000 conference, 21-22 June 2000, pp 6.7.7.)
115. Radio transmitting station interferes with railway train brakes
A European train operator had a problem on a section of track near a radio transmitting station. When a certain type of locomotive was passing by the radio station its main circuit breaker would open, causing it to brake. It was found out that the temperature sensors within the traction motors picked up the radio signal. The cables to these sensors weren’t screened. A modification to this would have been very expensive as the sensors are mounted within the winding of the motors.
The solution chosen was to increase the time window for the signal to be above a certain limit before the control would take action. Due to the long time constant of the thermal behaviour of the system, this solution was acceptable and sufficient.
(Sent in by Jennifer Cortese, Melbourne, Australia, December 2000)
116. Diesel engine spurious start-up caused by taxicab transmitter
I was lying on my back underneath a diesel engine (part the emergency power generator of a hospital) with the sump off, doing some work on the bearings. There was not a lot of room between the engine and the floor. The diesel generator was turned off, that is to say the OFF pushbutton on the control panel had been pressed and the controlling PLC’s display showed the OFF condition.
Suddenly, the diesel’s starter motor operated and the engine began to run, with the crankshaft whirling around a couple of inches above my nose. Very cautiously, I slid out from underneath. I discovered that a ‘bush taxi’ that called at the hospital was responsible. These bush taxis had extra powerful radio transmitters fitted, so they could stay in touch with their base when very far away in the bush. Keying the powerful transmitter at the hospital entrance created enough interference for the generator’s controlling PLC to think it had received the start command.
(Attendee at an EMC seminar in Sydney, Australia, November 2000.)
117. AS$8 million machine spurious start-up caused by transients
We were close to finishing the construction of an eight-million-dollar mining machine in a cavern in Australia. The operators of the mine had a central control room from which they wished to be able to exert manual control over any machine in the mine, even though the machines were automatic or had local control. Accordingly, the mine operators ran their own cables from their control room and connected them to spare inputs and outputs on the PLC for each new machine, also making the necessary software modifications themselves.
Suddenly, while we were standing by the machine, it started up of its own accord. Luckily, no-one was working on it at the time, although they could have been, but it was still a very serious issue as the machine had not yet been filled with lubricant and could easily have been wrecked. It turned out that no special precautions had been taken with the cables from the control room to the PLC, or with the software changes, and a transient interference with the new cables had caused our machine to start up unexpectedly.
(A different attendee at an EMC seminar in Sydney, Australia, November 2000.)
118. Spurious start-up of machine with 5 metre blades
I was visiting a company that made cutting machinery for carpet manufacturers. These machines had blades 5 metres wide, and very sharp. Adjusting the blades to get a good cut over the whole 5 metre width involved careful adjustments, and I noticed that some of the engineers would lie under the blade while making these adjustments.
I also noticed that the control panel (which used low-cost PLCs and not safety-critical types) was in ‘single step mode’ during these adjustments, and not ‘locked-out’ at its main electrical supply disconnector. I asked the Chief Engineer if they had ever had one of these machines start up on its own when in this mode, and he said that it had been known to happen, presumably due to transient noise on its mains supply or picked up by its cables.
(From an EMC Consultant who wishes to remain anonymous, February 2001)
119. Possibility of UWB interfering with GPS
I just had to write to you about the [November] editorial “Whose spectrum?”. It is right on the mark. However, I would like to point out that there is another crucial difference between ultra-wideband (UWB) devices and hair dryers in addition to the list that Charlie Trimble so appropriately collected; if you choose to shield the hair dryer or otherwise filter its electromagnetic emissions, it still functions as a hair dryer!
If in the future, UWB is (heaven help us) given the desired rulemaking, becomes as pervasive as that industry dreams it will, and then is found to jam GPS at large distances, there will be no technical remedy, just a face-off between two competing industries. To follow the thread of your editorial, if we must grant UWB an FCC Part 15 exclusion just because we have a precedent with other emitters in the band, then we are truly facing a spectral “tragedy of the commons”.
(Stephen Lazar of The Aerospace Corporation, writing to the editor of GPS World magazine, Page 6 of their January 2001 edition, www.gpsworld.com/gpsworld.)
(Editor’s note: ‘ultra-wideband’ radio communications devices use a train of very brief pulses occupying many MHz, even GHz of spectrum simultaneously, using time-domain techniques to distinguish one transmission from another unlike traditional radio that uses frequency domain techniques. Their transmitted spectra look like wideband white noise at relatively low power, and the effect of large numbers of them is to raise the noise floor considerably, to the point where the weak signals from GPS could be jammed. Also see Banana Skins December 1998 issue. The same technology is also capable of being used as a ‘personal radar’ useful for all sorts of things, such as checking someone’s heartbeat without contact, or detecting people through walls. We will no doubt be hearing a lot more about UWB in the future.)
120. How EMC techniques saved hundreds ofmillions of dollars
The new series of Australian banknotes have a plastic film embedded in them, RF welded into place. When the new bank note production line was first used, the emissions from the RF welder (dialectric heater) upset other printing machines and ruined large numbers of banknotes. They called me in and I fixed the problem, improving their productivity and saving them from burning hundreds of millions of misprinted dollars!
(From Chris Zombolas, EMC Technologies Pty Ltd, Melbourne, Australia, www.emctech.com.au.)
121. Police frequency freaks hospital
Further to confirmation that mobile ’phones can indeed interfere with the navigation systems and electronics on board aircraft, news arrives that the UK’s new £2.5 billion national police radio network is being urgently tested amid fears that it will interfere with vital hospital equipment and breath-test and radar speed machines. Until it is checked, police have been told to turn their new radios off in hospitals and near other vital equipment. There could also be problems at airports, ports and even in police control rooms.
The network uses a digital radio system called TETRA, or Terrestrial Trunk Radio. The handsets send out pulses at frequent intervals to the nearest masts, identifying their presence, but the pulses can affect the electronics of some types of equipment. The alarm was raised when Jersey police, who are already using Tetra, reported possible problems with their speed and drink-drive equipment. Scientists at the Defence Evaluation and Research Agency (DERA) have been commissioned to discover the level of interference and what else the radios could affect.
(From: The Times, January 2001, sent in by Harold Smart who saw it in the Royal Institute of Navigation Journal, January/February 2000 issue, www.ion.org.)
122. Interference clouds future of multi-billion police radio project
Police from the channel island of Jersey, which is going through pre-implementation testing of the TETRA technology, is advising its officers to be much more careful about using the equipment than was the case with previous kit. Because of fears of interfering with hospital equipment, the States of Jersey police have imposed tough rules on using equipment and ordered the lowest powered handset available.
The testing also threw up concerns that, according to a statement issued by the Jersey Police, “if a speed detection device suffered external radio interference, it was rendered inoperative”. There are also concerns about breath testing devices. According to reports police are being advised that they can only do breath tests 10m from handsets or 35m from more powerful car transmitters. This has raised concerns that the system, the price of which has already been a source of discontent with the old bill, will be turned off in many situations.
The Police Federation has raised concerns that operational effectiveness and even police safety will be damaged, and not improved, by the introduction of the technology. A spokeswoman for the suppliers of the technology, BT Quadrant, said that the equipment used complied with international standards. She compared the equipment to GSM phones which also have to be turned off in hospitals.
(Extracted from an article posted in The Register on 22nd Jan 01 by John Leyden, www.theregister.co.uk/content/5/16266.html, sent in by Graham Eckersall, G4HFG.)
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: https://www.emcstandards.co.uk/emi-stories, 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.
