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.
265. Radar detectors interfere with SKY TV
Radar detectors that warn drivers they are approaching a police speed trap can emit signals that cause interference to SKY digital television (and numerous other microwave communications systems).
Although it is suspected that this type of interference is widespread, only a small number of cases have been reported. This is because most people would attribute the freezing or break-up of their digital TV picture to a glitch in their equipment, or SKY’s transmission, rather than interference. Relatively few people notice if this type of interference always occurs when a particular vehicle (fitted with a radar detector) passes their property.
The European Commission’s Directorate on General Enterprise have been made aware that equipment approved to their Automotive EMC Directive 95/54/EC has been found to interfere with radio systems operating in the 10-20GHz frequency range. It used to be considered that products that came under the 95/54/EC and were ‘e’ marked were excluded from being covered by the EMC Directive 89/336/EEC and so did not require CE marking.
However, it is now the Directorate’s opinion that 89/336/EEC applies to all of the EMC aspects that are not covered by 95/54/EC. Since 95/54/EC only covers emissions up to 1GHz, 89/336/EEC covers emissions from automotive equipment from 1GHz to 400GHz. Sadly, most of the applicable test standards under 89/336/EEC only test emissions to 1GHz, but at least the Protection Requirements of 89/336/EEC require that no interference is caused regardless of the frequency.
In the USA, where satellite TV is not very common, significant interference has occurred to satellite terminals used to link retail establishments with remote computers for verifying credit card transactions. Accordingly, the Federal Communications Commission (FCC) has announced that from August 2002 all radar detectors manufactured or imported in the USA must meet the Part 15 emissions limits in the 11.7-12.2GHz band.
(“Proposed changes in the Guidance to the Automotive EMC Directive 95/54/EC and the EMC Directive 89/336/EEC to jointly impose both “e Marking” and “CE Marking” on vehicles and vehicle equipment”, ERA Technology Ltd, Safety and EMC Newsletter, Number 68, April 2003, page 7. Also see: “FCC stiffens rules for radar detectors”, Conformity, September 2002, page 8. And: “All radar detectors marketed must be FCC approved effective October 27, 2002”, DA 02-2852 October 28 2002, http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-02-2852A1.pdf?date=021028.)
When comparing the phenomena regulated by both Directives it becomes apparent that harmonised standards under 89/336/EEC cover a wider range of phenomena than regulated by 95/54/EEC. The latter Directive limits itself to regulating radiated emissions below 1 GHz and for safety critical components regulates higher levels of immunity. This thus implies that it doesn’t harmonise all the protection requirements specified in Directive 89/336/EEC, reason for which it is incorrect to argue that Directive 89/336/EEC doesn’t apply to such products at all. A logical line of thought is that it only ceases to apply for the phenomena, which are regulated by the automotive EMC Directive and thus continues to apply for all other phenomena.
(Taken from: “Guidance in the EMC guide on the relation of the EMC and Automotive EMC Directive” Brussels, 15 January, 2003, Ref: 07-28 EMC-AUTOMOTIVE, DG ENTR/G/3. Does this mean that motor cars should be CE marked, and have a Declaration of Conformity to the EMC Directive, after all?)
266. Examples of interference with satellites
The wake shield experiment was launched in February 1994, but the small satellite used could not be deployed due to EMI with its attitude control system. This was caused by inductive coupling (crosstalk) between the unshielded attitude control sensor cable and the power bus of the spacecraft. This was an unpleasant lesson learned at the cost of a failed experiment.
The Gamma Ray Observatory satellite experiment launched in 1991 experienced a transponder lockup that prevented the spacecraft from receiving control commands. EMI from a ground source (plus design problems) was the cause.
The NOAA-11 weather satellite was launched in 1988. In September 1991 a series of phantom commands were observed and determined to be caused by EMI due to a noisy VHF (Very High Frequency) environment.
The NOAA-12 weather satellite was launched in 1991. In September 1991 it experienced phantom commands when it flew over Europe, due to the heavy commercial VHF environment over Europe.
(The above incidents are items 2.2.2, 2.2.4, 2.2.5, and 2.2.6 in NASA Reference Publication 1374: “Electronic systems failures and anomalies attributed to electromagnetic interference” published in July 1995.)
267. Saturn Launch Vehicle interference
During on-pad checkout at the Kennedy Space Centre prior to one of the early development test flights of the Saturn launch vehicle, the range safety receivers detected an extraneous signal. Because these receivers processed commands for engine cut-off, arm and destruct, a thorough investigation was conducted.
The spurious signals were caused by the multitude of telemetry transmitters located on board to collect test data, however, none of these were operating near the range safety receiver frequency.
Further investigation determined that the various RF signals were ‘mixing’ and producing intermodulation products in a non-linear circuit created by metalwork that was not properly bonded, namely the hinged cable tray covers and chain handrails on the gantry.
(The above incident is item 2.1.1 in NASA Reference Publication 1374: “Electronic systems failures and anomalies attributed to electromagnetic interference” published in July 1995.)
268. Safety-critical residual current detector (RCD) tripped by mobile phone
The ‘incident’, which occurred at a site handling radioactive material in 1996(?) was as follows: It was noticed that use of a mobile phone within approx. 1.5m of a portable RCD caused the RCD to trip. The RCD was connected in the supply to a monitor for ‘in air’ alpha particles. The concern was that such monitors connected via RCDs could be inadvertently tripped without being noticed. This could result in a failure to detect hazardous radiation levels.
Although, as far as I am aware, there was no such failure in this case. Portable radios caused the same effect up to 2.5m from the RCD. This illustrates a general principle that where electronic devices are employed for ‘passive’ monitoring to reduce risks to health or safety, steps should be taken to avoid such false tripping resulting from EMI, and regular tests carried out to verify the operation of the monitor. Hopefully, the immunity of RCD’s has improved since the time of this incident, but the general principle remains.
(From Simon Brown of the UK’s Health and Safety Executive, 19th June 2003.)
