219. Examples of interference from the U.S.’s Food and Drug Administration (FDA)
The Food and Drug Administration (FDA) is aware of a safety issue that affects users of all electrical products. Specifically, electromagnetic interference is resulting in hazards to users and operators. Our purpose in writing to you is threefold: 1) to inform you of our involvement, 2) to encourage interchanges between professional and trade associations (medical and non-medical) to develop solutions, 3) to ask you to re-assess your product designs.
We are concerned about the response of electrically-powered products exposed to various electromagnetic environments and the consequences of that response. CDRH has received reports of malfunctions of medical devices and radiation-emitting electronic products due to electromagnetic interference (EMI), including radiated emissions, conducted emissions, and electrostatic discharges. Sometimes, the consequences were severe even though emissions were within currently accepted limits; for example:
- a monitor failed to detect a patient’s critical condition,
- a defibrillator failed to resuscitate a patient,
- a wheelchair suddenly moved towards street traffic,
- a laser beam went into the audience area of a light show,
- a radiation beam shutter did not close.
Electrically powered products can be sources of EMI, or unintentional receivers of electromagnetic fields, or both. The increasing use of electronics, proliferation of electromagnetic sources, and lack of electromagnetic compatibility (EMC) testing for many products has led CDRH to begin developing a strategy for EMC.
(Taken from “A Letter to Industry” – an open letter from the FDA’s CDRH (Center for Devices and Radiological Health) to registered medical device manufacturers, firms filing electronic product radiation reports, and related trade and professional associations, on September 18th 1996. The full text of this letter is at http://www.fda.gov/cdrh/emc/letter.html.)
220. Radio waves can cause unintended movements of electric wheelchairs and scooters
This is to let you know that laboratory tests performed by the Food and Drug Administration (FDA) showed that radio waves can cause unintended motion of powered wheelchairs and motorized scooters. …. The following information summarises what you should know about EMI. You may use this information to minimize the risk that EMI will affect your powered wheelchair or motorized scooter.
…. If my wheelchair or motorized scooter is affected by EMI, what kind of motion should I expect? This is hard to predict. It would depend on an number of factors, including: the intensity of the radio waves, the construction of the powered wheelchair or motorized scooter, whether it is on level ground or on a slope, and whether it is in motion or still. The motion can be erratic, with the powered wheelchair or motorized scooter moving by itself or coming to a sudden stop. Further, it is possible for EMI to unexpectedly release the brakes on a powered wheelchair or cause it to go in unintended directions. Some intense sources of EMI can even damage the control system of the powered wheelchair or motorized scooter.
.… What can I do to reduce the risk that my powered wheelchair or motorized scooter could be affected by EMI? Here are some precautions that you can take:
1) Do not turn ON or use hand-held personal communication devices, such as citizens band (CB) radios and cellular phones, while the powered wheelchair or motorized scooter is ON.
2) Be aware of nearby transmitters, such as radio or TV stations and aware of hand-held or mobile two-way radios, and try to avoid coming close to them. For example, a powered wheelchair or motorized scooter with an immunity level of 20 V/m should stay at least three feet from a hand-held two-way radio and ten feet from a mobile two-way radio.
3) Be aware that adding accessories or components, or modifying the powered wheelchair or motorized scooter, may make it more susceptible to interference from radio wave sources. (Note, there is no easy way to evaluate their effect on the overall immunity of the powered wheelchair or motorized scooter.)
(Taken from “Radio waves may interfere with control of powered wheelchairs and motorized scooters”, published by the Department of Health and Human Services of the FDA on September 20, 1994. Available as a download from the FDA’s website at http://www.fda.gov)
221. Examples of interference from NASA
NASA Reference Publication 1374 (RP-1374), “Electronic Systems Failures and Anomalies Attributed to Electromagnetic Interference”, can be downloaded in PDF format from the NASA Archive website at: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960009442.pdf.
Although it includes many case studies relating to the space program (some of which were very costly), it also includes cases from the marine, aircraft, automotive and medical industries. This publication is of great interest for electronics in general as it does not cover incidents relating to spacecraft charging from natural space plasma, which is of course peculiar to the space environment.
(From Władysław Moroń, Adviser to the President, Office of Telecommunications and Post Regulations, Republic of Poland.)
222. TV antenna boosters jam GPS over entire harbor and 1km out to sea
For months, the elusive culprit had jammed GPS signals in Moss Landing Harbor, Monterey California. The team of engineers roamed the waterfront with a spectrum analyser and receiver. They identified not one but two culprits, and unearthed evidence of a third, all of them readily available, commercial-grade television antenna boosters.
In April 2001 the captain of the research vessel PT SUR, based in Moss Landing, California, made a radio telephone call at-sea to one of the authors, stating that signal reception of GPS in the whole of Moss Landing Harbor was jammed. He was advised to contact the U.S. Coastguard (USCG) and the Federal Communication Commission (FCC). When the problem persisted for another month, we launched an effort at the local level to determine the cause of the jamming.
One of the major ships in the harbor paid for a technician and new equipment to fix the problem, but finally had to turn off GPS in the harbor area, give the alarm that GPS was off line, and use radar only for harbor entrances in bad weather.
We began our search for the source of jamming radiation in May 2001, spending several days looking for it. Two factors complicated the effort: the large number of metal objects that reflected the energy, and the shifting of the frequency of the emitter.
Only by turning off shore power to individual boats could we determine the actual emitter location. We contacted the boat owner and gained access, quickly determining that the emitter was a commercially available VHF/UHF television antenna with built-in preamplifier. The preamplifier was powered all the time, even when the TV was not on. In fact, the TV was seldom on, and most of the time the TV antenna was in a paint locker inside the locked boat. From this interior. Its emissions jammed all of Moss Landing Harbour and an area at least 1 kilometer out to sea.
A few days after Source-1 was removed, there were still long periods when our MBARI GPS receiver was tracking few or no satellites. The MBARI GPS receiver was being jammed during most nights. We conjectured that the jamming’s diurnal pattern derived from the temperature sensitivity of the second jammer’s center frequency. This turned out to be correct. This told us that we would have to search for the second jammer at night and early morning. Again the hunt was not easy. (They abandoned the search for Source-2 and instead went hunting for yet another jammer they had discovered, Source-3.) In the end, it turned out to be another commercially-available VHF/UHF television antenna on a boat, one dock over from Source-1.
The FCC has determined that the preamplifiers in Source-1 and Source-3 came from the same factory, which sold units to at least four well-known U.S. brand names of consumer electronics equipment. The bad units apparently began with a design change in late 2000; the number of units sold is not known to the authors.
The FCC made a few more attempts to locate Source-2 during the summer. In the fall of 2001, the FCC succeeded in locating Source-2. It again turned out to be a VHF/UHF television antenna with preamplifier.
Source-1 had the highest level at -96 dBm. Its location is known to have been 325 meters from the MBARI antenna. It was at an elevation angle of -2.5 degrees. While the beam pattern of Source-1 is unknown, if it were omni-directional, it would exceed the FAA specification for aircraft GPS receivers for GPS landing systems at a range of 50 kilometers or more. It is known to have caused marine GPS receivers to lose lock out to 3 kilometers.
Conclusion: In one small California harbor, at least three emitters capable of jamming commercial GPS receivers were present. Locating these sources proved difficult. The existence of the jamming was well-known in Moss Landing Harbor, and reported at least once to the appropriate agencies. However, the problem persisted until local engineers and scientists hunted down the worst offender.
(The above was extracted from “System Challenge – The Hunt for RFI – Unjamming a Coast Harbor” by James R Clynch, Andrew A Parker, Richard W Adler and Wilbut R Vincent of the Naval Postgraduate School, and Paul McGill and George Badger of the Monterey Bay Aquarium Research Institute, GPS World January 2003 edition, pages 16 – 22, http://www.gpsworld.com. Note how much time and effort it took to identify the low-cost culprits.)
223. Unreliability of GPS-based navigation systems
In July 2001, the Subcommittee on Safety of Navigation of the International Maritime Organisation (IMO) approved the draft revision of IMO Resolution A.815(19) World Wide Radionavigation system. Of particular interest in the Resolution is the requirement of signal availability of at least 99.8 percent over a 2-year period and continuity of service of at least 99.97 percent over a period of 3 hours for navigation on those harbor entrances, harbor approaches and coastal waters with a high volume of traffic and/or a significant degree of risk.
On most modern ships, (D)GPS is the only source of position information to the electronic chart (ECDIS) and to the mandatory onboard transponder of the Automatic Identification System (AIS). Especially on high-speed craft and on one-man bridges there is little time to cross-check navigation accuracy with other available information, such as radar. False position information to the AIS could even lead to “AIS-assisted collisions”.
The Volpe report on GPS vulnerability recommends that public policy must ensure, primarily, that safety is maintained even in the event of loss of GPS. The reasons for possible loss of GPS are well described in the Volpe report and in other publications. However, IMO or other maritime bodies do not address solutions for the case of loss of GPS (yet). The future of the Northwest European Loran-C system is unsure after the end of the agreement between the participating countries in 2005; many world-wide maritime areas are not covered by Loran-C. Other terrestrial navigation systems for maritime application have been phased out. The combination of GPS and Galileo will increase the availability of signals and the possibility of Receiver Autonomous Monitoring (RAIM) but Galileo is also vulnerable to interference or jamming.
(Extracted from the contribution by Jac Spaans, Professor Emeritus, President of the Netherlands Institute of Navigation, to the review entitled “Directions 2003” in GPS World, January 2003, pages 28 and 30, http://www.gpsworld.com. We note that GPS systems are cheap to implement because the U.S Military pays for the satellite system. No doubt this is why so many people want to use them, even for safety-related or safety-critical functions, despite their obvious shortcomings. The “Volpe” report can be downloaded via http://www.navcen.uscg.gov. The reason why this item is included here, is that one of the main causes of unreliability in GPS is electromagnetic interference.)
224. Jam GPS over radius of 100 miles, for just US$40
Electronic signal jamming devices that can be purchased through the Internet for less than $40 could play a decisive role in the effectiveness of possible U.S. air strikes against Iraq. According to recent report in the Wall Street Journal, U.S. congressional and military leaders are becoming increasingly concerned that widely available and relatively inexpensive devices that jam signals from GPS satellites could hamper efforts to effectively target high precision bombs in densely populated areas (such as Baghdad). Such munitions are now largely dependant on signals from GPS to deliver their warheads within 10 to 30 feet of their intended target.
Even the smallest of jamming devices can be remarkably effective at scrambling signals from GPS satellites. A 19 pound device demonstrated at the Paris Air Show in 1999 by a Russian company claimed effective jamming of GPS signals for more than 100 miles. The device boasted a puny 4 watts of power.
(From “GPS Jammers Could Hinder Attack on Iraq”, in the “Newsbreaks” section of Conformity, November 2002, page 8. The Wall Street Journal Article referred to in the above was “US Bombs May Not Find Targets In Iraq Due to Satellite ‘Jammers’”, Tuesday, September 24, 2002, http://www.wsj.com.)
225. Baby alarm interferes with aircraft communications near some UK airports
A well-known make of wireless baby alarm is known to cause occasional interference with aircraft communication as the planes approach some airports in the UK. It is not the wireless technology in the baby alarm that is the problem, it is their plug-top power supply, which uses a switch-mode converter. A faulty batch of power supplies was shipped with the baby alarms, and although they function well enough they emit powerfully on VHF radio channels used by National Air Traffic Services Ltd. (NATS).
The interference is particularly difficult to detect on the ground but when NATS is informed of problems of this sort, they are able to overfly the troubled area with a specially equipped aircraft, partly funded by the Radiocommunications Agency (RA). When the aircraft has located the source of the interference, NATS will send in a specially equipped road vehicle which identifies the house concerned.
Officers from the RA then exchange the faulty plug-top power supply and send it back to the baby alarm manufacturer, who ship a (non-VHF-transmitting) replacement. It is a lot of trouble to go to for a low-cost electronic item, but flight safety requires us to do it.
(From Tom Perry, UK Civil Aviation Authority (CAA), http://www.caa.co.uk.)
226. Potential for xDSL to significantly raise the radio noise floor
Mass deployment of ADSL systems in Greater London has the potential to exceed the ITU noise floor. In addition, the emission level is predicted to exceed the maximum co-channel interference level of an airborne ADF (Automatic Direction Finding) receiver by up to 15 dB over the centre of the city, reducing to 2 dB at the edge of the city.
Mass deployment of VDSL systems has the potential to increase the noise floor by up to 18 dB at 10MHz at a height over central London of 100m. At the centre of London, the cumulative emissions level exceeds the ITU noise floor at all heights up to 20 km. At the edge of the city, an increase in the noise floor of between 5 dB – 8 dB is anticipated at a height of between 5 km – 10 km.
(Extracts from: “Prediction of interference due to telecommunication drop wires in the ADSL and VDSL bands” by A R Bullivant or W S Atkins Singapore Pte Ltd and A J Maddocks, ERA Technology Ltd, presented by Tony Maddocks at the IEE Seminar “EMC – It’s nearly all about the cabling” at Savoy Place, London, January 22nd 2003, http://www.theiet.org. ADSL and VDSL are the technologies used for delivering ‘broadband internet access’ over ordinary telephone wires.)
227. GPS is vulnerable to jamming
The U.S. Department of Defense will use in-theatre jamming of the L1 signal to deny its adversaries the use of GPS. While jamming GPS signals has always been a military option, its use became a necessity following deactivation of Selective Availability. In addition to such military procedures, terrorists might try to jam the GPS signals using easily constructed equipment. GPS signals are also susceptible to unintentional jamming.
The civil GPS community got an eye-opener in 1997 as well. First, the Russian company Aviconversias announced in September that it could deliver a commercial GPS/GLONASS jammer capable of blocking civil GPS receivers within a radius of 200 kilometers. Then military GPS testing in the New York area in December caused a number of GPS receivers in civil aircraft to lose track of GPS signals during approach to Newark International Airport. Thus it was confirmed that civil receivers were vulnerable to jamming, and at the same time, that jamming equipment was commercially available.
One of the most important studies in this field, and – coincidentally – with very good timing (released one day before the 9/11 attacks on the World Trade Centre – Editor), was the so-called Volpe report on the vulnerability of GPS which concluded that, like other radionavigation systems, GPS is vulnerable to jamming, and that jamming of GPS could jeopardize safety and have serious environmental and economic consequences. The report also concluded that increased use of GPS in civil infrastructure makes it an increasingly attractive target for hostile activities by individuals, groups and states. At the same time, the analyses underlined the commercial availability of equipment for jamming purposes.
(Extracts from “Jamming GPS – Susceptibility of Some Civil GPS Receivers”, by Börje Forssell and Trond Birger Olsen, in GPSworld, January 2003, pages 54 – 58, http://www.gpsworld.com.)
228. Reliability is important for GPS
In looking to the future, with GPS playing an increasingly important role in our daily lives, we must ensure that we maintain that reliability. With safety and security as its top priorities, the department has developed a 14-point action plan to mitigate any potential vulnerability. We are working closely with the Department of Defense in their GPS modernization efforts, redoubling our efforts to protect critical spectrum resources, and developing capabilities to locate sources of interference quickly.
(An extract from an article by Jeffrey N. Shane, Associate Deputy Secretary, U.S. Department of Transportation,
in “Directions 2003” in GPSworld, December 2002, Page 24, http://www.gpsworld.com. Forgive us for being critical, but it seems to us that the vulnerability of GPS is actual, not potential; and that sources of interference need to be located considerably more quickly than the several months reported in item 222. The reason why this item is included here, is that one of the main causes of unreliability in GPS is electromagnetic interference.)
229. GPS signal reception will be more challenging in the future – example of UWB
The FCC published a rulemaking authorizing unlicensed ultra-wideband (UWB) signal emissions. Many believe these have the potential for interference to GPS and to raise the noise floor.
The GPS signal reception environment will be more challenging in the future – the UWB rulemaking is a bellwether event. There is incredible demand for wireless capability, which will only grow in the future. At the same time, dependence on GPS-based POITIME is increasing in military systems, in “safety-of-life” navigation systems, and in essential transportation, communications, financial, timing and other infrastructures.
(Extracts from an article by Jim Doherty, Senior Analyst, Institute for Defense Analyses; member, Independent GPS Assessment Team, in “Directions 2003” in GPSworld, December 2002, page 26, http://www.gpsworld.com. Note that the GPS satellite signals are so weak that they are already below the ambient noise floor even in the quietest locations on the earth’s surface. Software algorithms are used to make them readable. UWB is bound to be widely adopted because of its low cost. )
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.
