Banana Skins 201 - 225
201 Please could you help with a project I have, investigating potential safety implications of mobile phones and aircraft. Three potential hazards come to mind.
1). While using mobile phones on the ground, whilst refuelling the aircraft, the displacement of air at a rate of approx. 1500 lt. per minute out of the tanks as vapour spill from vents at the wing tips. They are not intrinsically safe, so what energy is required to ignite fuel vapour? (I have personal experience of seeing the results of a person with a mobile phone strapped to his belt while filling his petrol tank. The mobile rang, igniting the vapour, and causing a jet bast from the tank which unfortunately took all the skin off from his wrist to his elbow).
2). Batteries should one become damaged and or shorted causing a fire what would be the possible fire hazard and what extinguishant should be used?
3). Potentially the worst case scenario RF break through from the mobile into the systems. They often can be heard over radios when transmitting in the vicinity of the receiver, a unwanted signal in my view, therefore what could happen if the signal is induced into and reacted upon in one of the many other systems? Again personal experience has shown of signals in an industrial process line where a 3 watt transceiver was being used some 15 meters from a large electronic motor control center, which sent motors into random speeds simultaneously causing major stoppages for the process line and months of these random transients to get solved. From an aircraft's point of view I have experienced transmitting from the aircraft's fitted VHF Transmitter on a particular frequency and the aircraft pitching nose down some 20deg while the autopilot was being used.
(A query made by Paul Barnes to an IIE Special Interest Group on the 2nd February 2002)
202 One of my first business trips after I got out of college was going to Chemical Bank in New York City, because one of the Sycor 250 terminals (for which I had written the firmware) would lock up every night. The hardware designer and I installed some hardware and software monitors on this unit, and left for the evening. Next morning we returned, and discovered that it had died shortly after 11pm-- the very time that the cleaning people were making their rounds! We discovered that the cleaning people were plugging their industrial vacuum cleaners into the same wall outlet as our terminal because it was convenient. I think that the bank changed to a simplex wall outlet there, and that solved the problem. (John Barnes, dBi Corporation, from a thread entitled Re: Voltage Spikes on Power Lines etc on emc-pstc on 14/03/02 23:14:43)
203 I discuss problems with powerline-spikes in chapter 8, Designing Power Supplies, of my book Electronic System Design: Interference and Noise Control Techniques (Prentice-Hall, 1987, now out of print). For equipment that will be used indoors, you should try to design your equipment to be immune to 6kV spikes. That is approximately the voltage at which our wall outlets arc over. (John Barnes, from the same thread as above)
204 The Enforcement Bureau of the FCC is taking strong action against retailers who are illegally marketing non-compliant equipment, specifically long-range cordless telephones. The Commission has initiated action against New Image Electronics (NIE), a Miami, Florida electronics store, for selling long-range cordless phones designed to operate on civil aviation frequencies.
The agency's action followed a six month investigation that began in February, 2001 when the FCC's Enforcement Bureau received reports from the Federal Aviation Administration (FAA) of sporadic, but potentially harmful, interference to aviation frequencies in the Miami area. FCC agents traced the interference to NIE, and investigators visited the store on at least two separate occasions, actually purchasing a long-range cordless telephone during its second visit. Not surprisingly, the purchased phone possessed none of the labeling or FCC authorization required for marketing the device in the United States. In its response to the Commission, NIE did not deny that it had sold the phone to the FCC's agents, but claimed in its defense that their clerk had mistakenly believed that the phone was being sold for export when one of the agents gave his address as "Puerto Rico." In its forfeiture decision, the FCC noted that Puerto Rico is part of the United States.
The Federal Communications Commission (FCC) has also taken action against two other Miami-based retailers for illegally selling long-distance cordless telephones. The Commission has issued monetary forfeitures to Electronics Unlimited and Lightning Electronics for the illegal marketing of non-compliant, high-powered cordless phones. (From Curtis-Straus update for April 2002, via Conformity Magazine).
205 I was asked to do EMC tests on a multi-channel digital location recorder designed and built by the R&D department of a well-known record manufacturer. The recorder was housed in a 19" rack unit and controlled by software running on a laptop computer, via RS 422. The audio results were said to be excellent, but they invariably had problems with the control functions. On the last recording session, the machine went into record mode as requested, but during the session, control of the recorder was lost. No command would allow the engineers to stop the machine or come out of record mode. The whole system had to be re-booted before they got control back. This was a classical orchestral session with 80 musicians, so the problem could have been expensive.
I placed the recorder unit in the EMC test chamber, connecting the system up normally, but with the laptop computer outside in the control area. This was to isolate the two different parts of the system. The recorder unit passed the basic emission tests when running in record or playback mode on its own. But when the RS 422 line was connected between the laptop computer and the recorder rack, the system failed the radiated emission test by a wide margin.
If the RS 422 cable radiated interference, it was very likely that the same cable would receive interference. I set up for the conducted immunity test. The cable, carrying signal or control data, is bombarded with a known level of RF from a computer-controlled oscillator/power amplifier, with the generated RF modulated by a 1kHz sine wave. The equipment under test is monitored to check if interference to the wanted signal can be detected in the main signal path or on the control data. Since the problems with the recorder involved the control data, we decided to test the RS 422 cable first.
The RF oscillator automatically sweeps through the test frequency range under computer control. Any problem that occurs is picked up by a volt meter/detector and logged in the test file. If necessary, fault events can be manually entered via the computer keyboard. The recorder unit was put into record mode and I started the test. At first all went well. But, as the modulated frequency approached 8 MHz, the time code display on the laptop screen stopped. All other controls seemed still to be working. However, at about 16 MHz, a second event was detected, and the laptop had lost control of the recorder unit. The recorder was permanently in record mode! I put the EMC test system in pause, and rebooted the recorder and laptop. Restarting the test at 18 MHz, everything was working properly until the modulated RF approached 33MHz (the bus/processor frequency of the recorder electronics). Multiple events were detected and control of the recorder system was lost once more and the laptop crashed. To cut a long series of tests short (similar problems were encountered on the other side of the recorder’s processor/bus frequency) - the problem was obviously interference on the RS 422 data communication circuit. But how could this be the case? RS 422 is a balanced transmission system and the cable was shielded.
An inspection of the RS 422 connectors at each end of the circuit revealed the following:
i. The connector at the laptop end had the cable shield correctly bonded to the chassis.
ii. The connector at the recorder unit end was an insulated component. The cable shield connection was wired directly to the logic 0V track on the printed circuit board (the digital version of the pin 1 problem).
iii. The custom made RS 422 cable had the cable shield connected to the recorder unit end only. The cable was constructed in this way, because the engineers had found that hum was introduced into the recorder when the RS422 cable was connected to the standard desktop PC used during the design phase of the project.
Thus, any interference current induced into the cable shield of the RS 422 data communication circuit was injected directly into the recorder unit’s ground conductor, allowing interference currents to flow in the RS 422 I/O electronics, resulting in poor or bad data on the RS 422 communications circuit. The laptop (or any other) computer, and the recorder was, at the very least compromised, by any interference induced on the RS 422 cable shield. (From Tony Waldron, 8th Jan 02)
206 Dear Ann Landers. I've always had trouble with peripherals. Keyboards and mice that were CE marked and looked like such good prospects have mostly turned out to be fickle. Well, I've been involved with a touchpad for about five months now. When I first bought it, we were so happy. Whenever we were together it, it could read my mind. A tap of my finger and it knew just what to do. And then this ESD gun comes along. One zap and BOOM! The touchpad turns its back on me. It won't respond at all! I tried talking to it...but it just gave me the cold shoulder. I suggested counseling...still no response. I threatened to go and get a mouse...no response. Well, I finally had to just take a deep breath and go through with it. I cycled power. Well it now responds to me... but I don't know if I'll ever trust it around an ESD gun again. I don't know if our relationship will ever be the same. Signed "Out of touch in New York"
OK, OK, the real question is... does anybody have some words of advice regarding touchpads. I am testing a unit which consists of a keyboard/touchpad combination. The touchpad is approx 1.5" x 1.5" and is able to sense a sliding or tapping finger. The touchpad is used to perform all of the functions that a mouse typically performs. I am assuming that it has some sort of capacitive sense circuit which can tell when your finger slides across the pad or taps on the pad. I have one that gets all out of whack with 8KV ESD. i.e. the touchpad becomes unresponsive and it stops software execution in our host system. Unfortunately, this is one of those instances where we don't build the keyboard/touchpad; so my bag of fix tricks is limited. Probably limited to seeing if another manufacturer produces a keyboard/touchpad with better performance. Or, am I slamming my head against the wall on this one? The keyboard/touchpad is already CE marked by its manufacturer. Is his typical? Are all touchpads (even CE marked ones) ESD sensitive? Do I just live with it? Am I over-testing this touchpad? Overall... I have had REALLY bad experiences with CE marked keyboards and mouses. Now I have trouble with our first touchpad. We typically use a capacitive filter on our inputs and we typically put a ferrite on the cable...yet still trouble. Is this typical of what others see? (From Chris Maxwell 02/01/02 21:56:34 via emc-pstc. Note: Ann Landers is a magazine’s “Agony Aunt” in the USA.)
207 Over the past couple of years, there has been extensive discussions of the potential interference that ultra-wideband (UWB) radio signals might cause to GPS once UWB devices proliferate across the planet. But GPS is also susceptible to interference from more conventional transmissions both accidental and intentional (jamming). For example, a particular directional television receiving antenna widely available in the consumer market contains an amplifier which can emit spurious radiation in the GPS L1 frequency band with sufficient power to interfere with GPS reception at distances of 200 meters or more. Harmonic emissions from high-power television transmitters might also be a threat to GPS. Furthermore, the GPS L2 frequency is susceptible to interference from out-of-band signals from transmitters operating in the lower part of the 1240 to 1300 MHz band which is shared by terrestrial radiolocation services and amateur radio operators. As for intentional interference, the weak GPS signals can be readily jammed either by hostile forces during conflicts or by hackers who could easily construct a GPS jammer from a surplus home-satellite receiver.
I have experienced the effects if RFI on GPS in Germany and some neighbouring countries since 1995. During this time I only experienced RFI to the GPS L1 frequency twice. In 1997 near the Swiss airport of Lugano, signals emitted from a permanent transmitter operated by the Italian military were detected (see Figure 3). In February 2002, for 20 to 30 seconds an unknown interfering signal with a frequency of 1570.96 MHz disturbed the reception of L1 at Frankfurt Airport and surrounding areas up to a distance of 150 kilometres (see Figure 4). While Geodetic receivers exhibited a loss-of-lock, a certified aviation receiver merely experienced a degradation of the S/N. Dual-frequency GPS users routinely detect interference to the GPS L2 frequency in Germany, Switzerland, and The Netherlands. In all cases the sources are amateur packet radio transmitters in the frequency band between 1240 and 1243.25 MHz. Such transmitters are called “digipeaters” (short for digital repeaters or relays). They are part of a Europe-wide network of a kind of wireless Internet operated by radio amateurs (see Figure 5). They cause interference to dual-frequency GPS receivers operated by researchers at several universities as well as by geodesists and surveyors. Figure 6 shows a comparison of the spectrum of such signals with a susceptibility curve representing the interference power required to degrade the S/N by 10dB. (Two extracts from the text of: “A Growing Concern – Radiofrequency Interference and GPS” by Dr-Ing Felix Butsch of Deutsche Flugsicherung GmbH (DFS) in GPS World, October 2002, pages 40 - 50.)
208 Early field trials in UK, Germany and Switzerland showed excessive radiated emissions (up to 40dB) above NB30 RegTP limits, which are about 20dB more relaxed over the 4/2000 RA version of UK MPT 1570 in the short wave spectrum. Broadcast, military, commercial as well as licensed amateur radio services started seriously objecting to a nationwide implementation of PLC. (PLC = Power Line Communications, basically sending telephone or Internet data over existing mains wiring and cables – Editor)
Far field effects and underestimated PLC system antenna factors  lead to short wave signal mirroring at the ionosphere. That is today not at all taken into account by officials in the ministry of economy in Berlin, which supervises the RegTP agency, the equivalent to the FCC US. These sky wave propagation effects might lead to background noise increase  also outside Europe. Sensitive receiving sites in Germany may experience, based on first simulations, degradations of 10 to 40dB! This is unacceptable for security agencies in the present political scenario.
The introduction of power reduction in broadcasting, due to digital technologies, reducing transmit power and therefore lowering electromagnetic pollution or heath hazards, become useless if at the same time the signal noise ratio will be PLC degraded.
Reports on publicly available, new measurements data from PLC modems/systems (e.g. ASCOM). Some indicating serious legal and technical trouble in wide spread PLC field trails systems.
Suspicion arouses, due to questionable promoter companies, seemingly forcing contracts with non-discloser agreements to be signed by their clients. This could hamper independent measurements.
Everybody is fighting physics. Due to Shannon, signal to noise ratio (typ. 15dB) is EMI relevant. PLC signal level, modulation and existing line noise are important to bridge the distance without costly repeaters. The PLC community is therefore fighting for “better”? less stringent regulations and want new EMC standards.
Little attention was formerly given to commercial System EMC; box testing was rather dominant. Finally, the commercial EMC community is forced into System Thinking! Cable TV systems started interfering with air traffic control over major German cities.
Typical test problems are identifying PLC Interference in bands <30 MHz, receiver jamming, time variant EMI. It takes wireless experts to be sure it is PLC and not other EMI. Normally at CW, AM, SSB, the whole receive spectrum is experiencing a massive noise floor increase (sounds like an old steam locomotive sometimes), resulting in total blocking. The sensitivity is wiped out.
Generally speaking there is very little willingness of the PLC people to talk technical even today.
On the official side, however, 100 serious, professional NB30 objections, some demanding even lower limits, filed to RegTP, were politically ignored by the ministry of economic affairs last year when NB30 came out. Reliable sources indicate, Federal Cabinet Minister Mueller (Economy) – originating from RWE (a company which is active in the PLC business – Editor) – before entering his political career in the SPD government – wants to return to his old company!
(A number of extracts from: “Update on Power Line Telecommunication (PLT) Activities in Europe” by Diethard Hansen of Euro EMC Services (EES) www.euro-emc-service.co.de, chairman of ATRT WG PLC, RegTP, Germany, presented at the IEEE’s International EMC Symposium held in Minneapolis, Minnesota, August 19-23 2002, and published in the Symposium Record on pages 17 - 22.)
209 Array-pattern nulling effects have become an important field of study recently due to the increased pollution of electromagnetic (EM) environments. These techniques reduce degradation of signal-to-noise ratio (SNR) performance due to undesired interference in radar, sonar, and communications systems. (Taken from “Reduce SNR Degradation in EM Environments Using a Nulling Technique” on page 56 of Microwaves and RF Journal, September 2002.)
210 EMI and RFI are not new phenomena. They are problems that have been around for years. When I was a small boy (which is longer ago than I will admit), I grew up across the street from a ham radio enthusiast named Bob Beebe, W71GM.
Bob had a powerful one-kilowatt linear amplifier for his ham rig, and a rotating beam antenna on his roof that covered more area than his roof did. We could hear him on every electrical appliance we owned. His calls are indelibly etched on my memory: “Hello, CQ, CQ, C. Hello CQ, CQ, CQ. This is W71GM, I Got Manilla.” (Manilla was the name of his wife!) Every time we got a new radio, we’d have to call Bob to come over and wrap it in copper or place ground wires all around it in order to shield out his emissions.
In another life I ran a company that made weighing systems for industrial trucks – i.e., scales to make sure trucks were within legal limits. They were portable, could be towed behind a police car on a small trailer, and used portable electronics that plugged into the car’s cigarette lighter. They ran off the same electrical system the police radio did, and the indicators were often placed right next to the radio or on the car roof, right next to the antenna. Immunity to RFI was a significant design requirement.
We had just finished a complete redesign of our indicator family. We had access to a screen room facility and a technician through another company, so we went there to do the EMI/RFI testing. During the very first test, however, the indicator went totally off-scale! No matter what we did we could not quiet down the indicator. After two hours of tweaking we got some improvements and then hit a plateau. No matter what we did we could not quiet down the indicator. The screen room technician finally spoke up and asked us what the input circuit looked like. We told him it was a high-gain differential amplifier, which then fed an A/D converter. He asked us what part number the amplifier was. We told him. It was a commonly available amplifier made by at least four or five manufacturers. He then asked us who manufactured the part. We told him. He then told us that particular manufacturers often had RFI problems with its parts and why didn’t we buy the same part from a different vendor. We did, and the RFI problems almost totally went away. It took us only a few more hours to achieve the RFI objective and the product then successfully went into production.
There was no clue in any of the published specification from any of the manufacturers of this part number that there would be differences in RFI sensitivity between product offerings. We had no reason whatsoever to suspect that part. We might have struggled with that design for months if that technician had not put us on the right path. There are two morals to this story:
- A good technician with experience can be more valuable than someone else with all the university degrees in the world.
- There can be subtle differences inside IC packages in otherwise identical parts that may only be determined by laboratory testing or trial.
More than one engineer has been ‘burned’ by a part that behaved unexpectedly. Sometimes, as in this case, there are simply differences in design or manufacture or otherwise “identical” parts. Sometimes a supplier changes a manufacturing process without telling anyone. Often this involves the implementation of an improved process, which coincidentally may offer faster rise times. Perhaps the manufacturer thinks that the change or improvement will have no particular consequence for anyone, and treats it as simply an in-line adjustment. But sometimes the faster rise-time results in timing or EMI problems that didn’t exist in the user’s design before. These can be particularly difficult to trouble-shoot, because people rarely equate the problems with a device, particularly a device that used to work just fine. (Extracts from “Lessons Learned the Wrong Way” by Douglas Brooks, President of UltraCAD Design Inc., www.ultracad.com, published in Printed Circuit Design magazine, September 2002, pages 30 and 39.)
211 Its an all too familiar scenario. You’re on the phone to an important customer, and – far from being able to hear whether he’s about to place the biggest order of the year – all you hear is an irritating crackling on the line.
Well, if its any comfort at all, you are not alone. Every year, thousands of users report that their critical business calls have suffered, for some inexplicable reason, from intermittent hissing, buzzing, crackling, and general interference. And when the phone companies investigate the phenomenon, they find nothing wrong. It’s a phenomenon that frustrates IT departments, telecoms engineers, sales managers, directors, in fact anyone that has to use a phone for business.
But this understandable annoyance that many of our industries suffer as a result of poor quality voice communications is nothing compared to the potential loss of revenue that can arise if their data systems suffer the same fate. And yes, you’d better believe that this is exactly what too many businesses are experiencing at this very moment.
I’m not suggesting that spikes and surges in the power supply are at the root of each and every problem, there is little doubt that they contribute to a significant number of these anomalies and aberrations. In fact, no lesser source than IBM’s Systems Development Division comments that “More than 80% of mains power problems are transient and noise related.” (Extracts from from “Communication problems – can tvss provide the answer?” by Mike Burgoyne of Advance Galatrek, in Components in Electronics magazine, September 2002, page 28.)
212 Two individuals have filed a petition with the FCC for reconsideration of a proposal that would require all electronic equipment to be shielded against electromagnetic pulse (EMP). With the prospect of future terrorist attacks clearly on their mind, the petitioners wrote that there is “the need for mandatory shielding to protect vital civilian equipment from the possible hostile use of an Electromagnetic Pulse (EMP)”. (Conformity, October 2002, page 46)
213 Every time the passenger ferry passed a certain point leaving the harbor, the automatic logging system was reset to its default settings. This always happened late in the evening, around 23:00. Strangely enough, this problem never occurred when the ferry was arriving at the harbor. After a thorough investigation, it was found that at 23:00 the stoves and ovens in the kitchens were switched off for the night. The transient overvoltages from the switch-off found their way to the bridge via the signal and power cables on board. The investigations also showed that no cable screens at all were correctly grounded.
The problem with the log was solved by introducing cable feedthroughs with electromagnetic disturbance protection, and by adding transient filters. (From Roxtec Ltd, page 23 of its booklet on ‘Cable and pipe transits for EMC’, December 2002, www.roxtec.co.uk)
214 Offshore oil and gas production platforms present an extremely difficult electromagnetic environment due to the amount of electrical and electronic devices crammed into a small space. In this case, a platform was anchored to the sea bottom, but its exact position was adjusted by thrusters, i.e. large electric motors driving propellers. The position of the platform was controlled by a computer system. The power and control cables, all screened, were routed from the control room on the bridge at the top of the platform, all the way down to the engine rooms far below. However, the cable feedthroughs were not protected against electromagnetic disturbances. Com radios were used both on board the platform and for communication with land.
When a technician tried to use his com radio in the engine room, the connection was continually bad. By letting the radio antenna touch a cable harness, the connection became much better. By feeding its electromagnetic energy into the cable screens, the radio got a much improved “antenna”. Unfortunately, the energy in the cable screens also went elsewhere. It went via the cable screens to the thruster control equipment, which interpreted the energy as a signal for adjusting the position of the platform. (From Roxtec Ltd, page 22 of its booklet on ‘Cable and pipe transits for EMC’, December 2002, www.roxtec.co.uk)
215 Bad EMC design caused operating problems in a quality control system in a foundry. The quality control system consisted of two subsystems, a robot subsystem and a measurement subsystem. An industrial robot picked up the heavy metal pieces and placed them at the measurement system. The measurement system checked for the presence of cracks in the metal. The electromagnetic environment was tough, with motor drives, arc-welding equipment and electric forklifts nearby. The problem was intermittent malfunctions in the entire system.
An investigation showed that the two subsystems interfered with each other. The industrial robot subsystem was carefully designed and installed with respect to EMC. The measurement subsystem, however, was not designed or installed with respect to EMC. The industrial robot subsystem was designed in a series of zones, where each zone was screened and equipped with Roxtec EMC cable feedthroughs.
The measurement subsystem was not divided in electromagnetic disturbance protected zones at all. Some of the cables were screened, while others were not. The screened cables entered the control cabinet via a large opening in the cabinet floor. The internal layout of the control cabinet was not done according to EMC principles. By redesigning parts of the measurement subsystem installation, it was possible to bring the operating problems down to an acceptable level. (From Roxtec Ltd, pages 24-25 of its booklet on ‘Cable and pipe transits for EMC’, December 2002, www.roxtec.co.uk)
216 A system to combat satellite interference, which costs operators millions each year in lost bandwidth, has been developed in the UK. Qinetiq’s satID system is designed to pinpoint ground bases inadvertently transmitting to an operator’s satellite, and using up some of their expensive bandwidth. The introduction of satellite services, the growth of personal satellite communications technology and congestion of the geostationary arc are increasing these interference problems, said Dr Rob Rideout, senior scientist for geolocation at Qinetiq.
“Satellites suffer a lot from interference, and as satellite transponder bandwidth is an expensive resource, to have that tied up is a big commercial problem for operators. The cost could run into many millions.” The vast majority of satellite interference is not malicious, but results from equipment failure of operator error. “Someone could be operating at the wrong frequency due to an equipment malfunction, or an operator could be pointing at the wrong satellite.” (Taken from an item by Helen Knight in The Engineer, 22 Nov - 5 Dec 2002, Page 11)
217 I was very interested in Rob Coppinger’s article ‘Jaguar tests cars for radiation’ (News, 1 March) which reported on Volvo’s decision to make adjustments to three of its models after they were found to generate a high level of electromagnetic radiation (EMR). I purchased a new VW Golf – which in common with all modern cars is full of high-tech gadgetry – and found that the electromagnetic fields were some 100–200 times greater than they had been in my old Peugeot. (Taken from a letter by Andrew Collett, Letters, page 36 of The Engineer, 22 Nov - 5 Dec 2002)
218 Allen Brown (Letters, September) asks whether there is any explanation as to why electric light bulbs sometimes ‘sing’ just before they fail. If a lamp filament fails during use and the break is not sufficient to interrupt the current, an arc will form across the break. Arcs formed in this way can be surprisingly long if the ends of the filament move. The singing is the sound of the this discharge, possibly acoustically modified by the thin glass envelope. Therefore filament lamps start to sing when they fail and not before. On a safety note, as this discharge is a UV source it is not advisable to look at a ‘singing lamp’ in view of the chance of ‘arc eye’, but to switch it off. If the singing was due to arcing across a break, the lamp will of course not light again.
I first met the ‘singing light bulb’ effect as a very junior technical assistant in a lampworks in the mid-1930s. Part of my job was to inspect the life-test racks twice daily, perform the BSI 161-1936 specified interruptions in supply, and record failures. Out of several hundred lamps on test, it was not uncommon to find one ‘singing’. The explanation is, of course, that the tungsten coil, having suffered long, has now parted at its weakest point and is now arcing using the remains of the tungsten coil as ballast. Left undisturbed it may run for some hours, depending largely upon the pressure and purity of the gas filling.
(These two contributions are from Alan Vicary and William J Chapman respectively, published in the Letters page of the IEE Review November 2002, page 25. We wonder whether any RF emissions measurements have ever been made on a ‘singing’ light bulb – we would expect there to be a significant emissions of broadband disturbances, probably modulated at the audible ‘singing’ frequency, peaking at the resonant frequencies of the mains wires. Filament light bulbs are often held up as an example of a “passive EM” device, i.e. one causing no electromagnetic emissions and unaffected by electromagnetic disturbances. But ‘singing’ light bulbs not too uncommon, and it seems that about 1% of ordinary coiled filament light bulbs are VHF transmitters at between 28 and 45MHz – see Banana Skin No. 159.)
219 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:
- monitor failed to detect a patient’s critical condition,
- defibrillator failed to resuscitate a patient,
- wheelchair suddenly moved towards street traffic,
- laser beam went into the audience area of a light show,
- 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 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 FDH’s website at http://www.fda.gov)
221 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: http://trs.nis.nasa.gov/archive/00000296. 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. (Many thanks to W?adys?aw Moro?, Adviser to the President, Office of Telecommunications and Post Regulations, Republic of Poland for drawing RP-1374 to our attention.)
222 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, www.gpsworld.com. Note how much time and effort it took to identify the low-cost culprits.)
223 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, 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/gps/geninfo/pressrelease.htm or direct from http://www.navcen.uscg.gov/archive/2001/Oct/FinalReport-v4.6.pdf.)
224 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, www.conformity.com. 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, www.wsj.com.)
225 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.)