302. Early colour TV interference from early police radio handset, warns criminals
About the time of the introduction of ‘Panda’ cars in the UK came a new Police hi-tech system known as the Personal Radio. In many Police forces this consisted of a pair of UHF radios, a transmitter and a separate receiver. The receiver was the more interesting of the two from an EMC point of view. Crystal controlled, single frequency and not much bigger than a packet of king size cigarettes, it had a vicious local oscillator that radiated very strongly.
The introduction of Police PR radios came about at the same time as the UK was just getting switched on to colour television. Regrettably, immunity from RF interference was not one of the finer qualities of this new entertainment system. I recall being told a story by Alan who was a licensed Amateur Radio colleague who happened to be a local Policeman. Apparently, invited (?) into someone’s home one day, the proud owner of his new colour television was watching a programme in glorious and over-saturated colour. Much to the annoyance of it’s owner, the television suddenly reverted to a black and white picture when Alan and radio walked into the room. Alan quickly turned off his PR receiver and the colour returned. Further tests revealed that even if he stood outside the front door of the terraced house with his PR receiver switched on, the TV was determined to stay in black and white until he walked away.
Allegedly this phenomenon was quickly communicated in criminal circles. Alan told me that it was no coincidence that more than one or two criminals were seen to run out of the back door before the bobby actually knocked on the front door. It seems that the early warning system was not just confined to Fylingdales in those days!
(Sent in by Graham Eckersall, G4HFG/W4HFG, Approvals Manager, Barcrest Group, July 13 2004.)
303. Power quality problems will get worse
The widely publicized breakdowns and subsequent blackouts in the public power networks of the Northern United States and several European countries are extreme examples of phenomena that occur on a smaller scale many times every day. Studies have shown that Dips, or “brown-outs,” and Interrupts, or “dropouts,” in the public power supply are tending to increase in frequency in our overstretched power networks, causing further degradation in the quality of the electric power supply. The results of power interruption can cause equipment reset and data loss, resulting in such consequences as breakdown of production or even danger to life.
The situation is not going to improve in the short term. As more functions are packed into increasingly smaller volumes, power consumption inevitably increases. Further, the increased use of microprocessors means that equipment incorporating them is potentially more susceptible to power line fluctuations.
(Taken from “Dips/Interrupts Testing Gets an Update,” by Martin Lutz and Nicholas Wright, Conformity, November 2004, page 12.)
304. Interference problems within a vehicle
When I sampled the Audi A3 Sportback recently with this same choice of transmissions, I could not decide which I preferred. For the GTI I emphatically opt for the conventional manual: even with the ESP (Electronic Stability Program) disabled, in versions fitted with DSG there was excessive interference from background electronic systems. Requests via my right foot for full-throttle acceleration would often be refused for several frustrating seconds.
(Note from the Editor: DSG stands for Direct Shift Gearbox, a semi-automatic gearbox with a steering wheel-mounted ‘paddle change’ and no clutch.) (Taken from: “Regeneration” by Peter Dron, a motoring review of the latest VW Golf GTI, in the Daily Telegraph’s Motoring section, Saturday November 6th 2004, pages 1-2, http://www.telegraph.co.uk.)
305. Interference can trigger airbags
Millions of cars have been recalled by the National Highway Traffic Safety Administration (NHTSA) and similar government safety agencies around the world, because of what is known as ‘inadvertent air bag deployment’. This includes cars sold by virtually every leading auto manufacturers including BMW, Chrysler, Ford, General Motors, Hyundai, Land Rover, Mazda, Mercedes-Benz, Saab, Toyota, Volvo and Volkswagen.
In addition to rough roads, light jolts, stones bouncing off the road surface and light bender-fender impacts at speeds air bag deployment is unexpected, the reasons for inadvertent air bag deployment include electrical shorts, dirty electrical connections, normal Supplementary Restraint System (SRS) wear and tear, static electricity and an incoming or outgoing cell phone call.
The following incident was reported by a driver in the USA, where cellphones use the PCS system and operate at 1.9GHz: “I was holding the phone at arm’s length so I could see the display to dial, in my left hand, so that it was almost touching the centre of the steering wheel when the air bag went off like a bomb. My hand was violently bent over so far that my fingers nearly touched the inside of my forearm. My head was wrenched backwards and to the left like somebody was trying to twist it off my neck. The pain of the air bag hitting my hand was excruciating; it felt like my hand was on fire and went on for what seemed like forever.”
The above driver did some investigation, and concludes that: “The thinking is that, in certain circumstances, the electric current coupled into the vehicle wiring from the cell phone antenna when it is close to an air bag igniter can be enough to cause deployment of the air bag. The antenna of my cell phone was, at most, an inch-and-a-half from the centre of the steering wheel when the air bag went off. A US organization involved in EMC testing said that the field at such a small distance from a mobile phone is likely to be in the region of 70V/m.”
It is impossible to say with absolute certainty that the cell phone set off the air bag. There are too many unknowns: the exact strength of the 1.9GHz current required to trigger the air bag; the exact distance of the cell phone antenna from the igniter; and the exact strength of RF field emitted from the cell phone’s antenna and its coupling factors into the vehicle’s wiring. (Editor’s note: But it seems very unlikely that the airbag should operate spuriously at the exact time that the cellphone was close to its igniter.)
The Automotive EMC Directive requires whole cars sold in Europe to be tested for immunity at a minimum of 30V/m up to 1GHz, in Europe. Since the above cellphone operated at 1.9GHz it is outside the range of this testing and the susceptibility of the car’s systems at this frequency is unknown. Also the testing is done with continuous wave (CW) and amplitude modulation (AM), not with the pulsed modulated (PM) signals typical of a mobile phone.
There are no legal immunity requirements for the USA – but all the reputable motorcar manufacturers apply immunity tests anyway to help reduce their risks of liability lawsuits. The EMC immunity specification employed by the manufacturer of the vehicle involved in the above requires electronic ‘components’ (subassemblies) to pass tests at 200V/m from 1-400MHz in a stripline or TEM cell, and 80V/m from 0-1000MHz in an anechoic chamber. Plus the whole vehicle is tested with radiated external fields at 200V/m from 6-30MHz, 140V/m from 30MHz-1.3GHz, and 70V/m from 1.3-3GHz – but these are the external field strengths: the fields inside the vehicle during these tests are not controlled so are unknown (the same comment applies to Automotive EMC Directive immunity testing).
The cell phone concerned operated at 1.9GHz, hence it was outside of the frequency range for the ‘component’ testing range – and the whole vehicle testing might not have created 1.9GHz fields at the steering wheel with field strengths comparable with those created by the close proximity of a cell phone. So neither this particular manufacturer’s tests, nor tests under the Automotive EMC Directive, could be sure to reveal the susceptibility of the airbag igniter to very close proximity of a cell phone transmitting at 1.9GHz. Note that about half of the cell phones in Europe operate at 1.8GHz, using the GSM system, so this brief analysis also applies to them.
(Adapted from information sent in by Martin O’Hara of the Automotive EMC Network by email in April 2004.)
306. Cell phones interfere with Lexus sensors
After incidents where cell phone calls apparently interfered with a sensor in some 1998 Lexus GS300 and GS400 sedans, the NHTSA recalled them (No. 98V080): “Due to a manufacturing defect of the yaw rate sensor for the vehicle stability control (VSC), the VSC can operate improperly if the sensor is affected by certain electromagnetic waves, such as from a cellular phone. Should this occur, the brake can operate unexpectedly, affecting steering and speed control, increasing the risk of a vehicle crash.”
(Sent in by Martin O’Hara of the Automotive EMC Network by email in April 2004.)
