let us make the discussion a little bit more to the point: The discussion about interference caused by unwanted emission of electronic equipment:
Limits for emission are essentially to protect (radio)receivers. (DOT) I have never met an equipment lacking immunity of any field strength at any frequency within 60 dB above the limits in f.a. CISPR22 that was not a (frequency selective) receiver. I cannot imagine any piece of electronics where such a field strength can interfere with its functioning without this equipment malfunctioning in 99% of civil areas due to intentional transmitters having the same field strength or higher. The level of emission from CISPR22 compliant equipment is that low that interference with radio receivers can only happen within the boundaries of less then 100 meters from the interfering equipment. We all know about the serious problems we have even measuring electrical or magnetic fields of this strength with especially designed equipment such as measuring receivers, actually operating close to the limits that technically can be achieved within the bandwidth defined. A side step: There are 2 sections in society that are of extreme relevance to the life of people involved. Both have been protected against influence of low and strong radiation by other measures then increased immunity: - one is aircraft equipment : esp. AM modulation systems for speech - medical equipment : IEC 60601 involves a very simple EMC test scheme older then the generics standard. The relevance of medical equipment's reliability need no further explanation, I believe. The earlier category is traditionally protected by stringent emission limits, and calls for it's relevance by lives depending on the equipment to justify protection of the spectrum for it's radio bands. No serious improvements therefore have been made in civil aircraft communication systems since Marconi (;<) The latter category protects it's interest by calling out for banning cellular in hospitals (as this was the first real sign of lack of immunity). Although we all understand the relevance of this measure, it makes no excuse for lousy immunity regulations for medical equipment. The emc immunity tests in Europe for a professional burglar alarm or tape recorder are substantially more severe as those for heart monitoring equipment. I believe this is an important lack of responsibility from both IEC and the industries involved, especially if we consider the costs of medical equipment. My understanding is that this discussion about EMC and safety (when spurious emissions are involved) is fed by (very short sighted) economical/traditional reasons within the categories of equipment manufacturers mentioned above. 1. The costs for better communication systems are not that high (apart from upgrading) and might easily be paid for if only one accident a year was saved. 2. AM based communications systems lack reliability, security and are much more prone to terrorist attacks (need this be explained ?) then simple small band FM or frequency hopping modulation schemes. 3. Costs for EMC are virtually zero if designed in from the first stage of development. Even substantial costs for increased immunity pay back for themselves by reduced ghost service calls and non defective returned equipment (failed only at customers premises), increased selling potential and customer satisfaction. Regards, Gert Gremmen, (Ing) ce-test, qualified testing =============================================== Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ =============================================== >>-----Original Message----- >>From: owner-emc-p...@majordomo.ieee.org >>[mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Ken Javor >>Sent: Tuesday, January 01, 2002 8:36 PM >>To: John Woodgate; emc-p...@majordomo.ieee.org >>Subject: Re: EMC-related safety issues >> >> >> >>If the length of discussion is proportional to the degree of controversy >>surrounding a subject, then the entire theory of electromagnetism is rife >>with controversy... >> >>The length of discussion is proportional to the complexity of the subject >>matter, and to the verbosity of the correspondent, a charge to >>which I plead >>guilty... >> >>JW said: "...The emissions from most of these products (except >>laptops) are >>quite weak. Since these are said to present a significant threat, I wonder >>that different systems within the aircraft's own electronic >>installation can >>practicably be prevented from interacting adversely." >> >>KJJ responds: Equipment designed for and installed in aircraft must meet >>RTCA/DO-160 (or the equivalent European requirement) Section 21 RE limits, >>which cover a wider frequency range (150 kHz - 1215 MHz), and are >>generally >>more stringent in limit magnitude, and the limit is imposed at one meter >>from the EUT, not 3 or 10 m. So for these reasons alone, >>aircraft avionics >>have more controlled RE profiles. Another issue which is >>unquantifiable is >>the degree of degradation of EMI performance a cheap portable piece of >>consumer electronics undergoes during its life relative to the performance >>of a single pristine unit undergoing EMI qualification. >> >>JW said: "... resistance to in-band interference can be very high if >>suitable modulation schemes and signal formats are used." >> >>KJJ responds: That is true for a high tech system like GPS. However the >>incident referenced here by implication, where a DC-10 nearly >>missed a final >>approach, occurred at least 10 years ago and was not under GPS >>control. The >>standard navigational aids: ILS, TACAN and VOR all have simple modulation >>schemes. ILS receivers have sensitivities on the order of -90 >>dBm, TACAN is >>-80 dBm, glide slope -60 dBm and marker beacon -50 dBm. >>> -- >> >>---------- >>>From: John Woodgate <j...@jmwa.demon.co.uk> >>>To: emc-p...@majordomo.ieee.org >>>Subject: Re: EMC-related safety issues >>>Date: Tue, Jan 1, 2002, 2:17 AM >>> >> >>> >>> I read in !emc-pstc that Ken Javor <ken.ja...@emccompliance.com> wrote >>> (in <20020101060002.GSJY27550.femail4.sdc1.sfba.home.com@[65.11.150.27]> >>> ) about 'EMC-related safety issues', on Mon, 31 Dec 2001: >>> >>>>KJJ response to JW: The aircraft receivers in question are just >>that, radio >>>>receivers, and as such are the sensitive victims protected by CE and RE >>>>limits as I described earlier. There is nothing controversial >>here at all. >>> >>> The length and detail of your response indicates otherwise! >>> >>>>The fact that personal consumer electronics may be able to affect such >>>>radios is not surprising. >>> >>> Well, it surprises me. The emissions from most of these products (except >>> laptops) are quite weak. Since these are said to present a significant >>> threat, I wonder that different systems within the aircraft's own >>> electronic installation can practicably be prevented from interacting >>> adversely. >>> >>>>It is not necessary to assume an out-of-band >>>>response, either. >>> >>> Of course not, but resistance to in-band interference can be very high >>> if suitable modulation schemes and signal formats are used. >>> -- >>> Regards, John Woodgate, OOO - Own Opinions Only. >>http://www.jmwa.demon.co.uk >>> After swimming across the Hellespont, I felt like a Hero. >>> >>> ------------------------------------------- >>> This message is from the IEEE EMC Society Product Safety >>> Technical Committee emc-pstc discussion list. >>> >>> Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >>> >>> To cancel your subscription, send mail to: >>> majord...@ieee.org >>> with the single line: >>> unsubscribe emc-pstc >>> >>> For help, send mail to the list administrators: >>> Michael Garretson: pstc_ad...@garretson.org >>> Dave Heald davehe...@mediaone.net >>> >>> For policy questions, send mail to: >>> Richard Nute: ri...@ieee.org >>> Jim Bacher: j.bac...@ieee.org >>> >>> All emc-pstc postings are archived and searchable on the web at: >>> No longer online until our new server is brought online and the old >>> messages are imported into the new server. >>> >> >>------------------------------------------- >>This message is from the IEEE EMC Society Product Safety >>Technical Committee emc-pstc discussion list. >> >>Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >> >>To cancel your subscription, send mail to: >> majord...@ieee.org >>with the single line: >> unsubscribe emc-pstc >> >>For help, send mail to the list administrators: >> Michael Garretson: pstc_ad...@garretson.org >> Dave Heald davehe...@mediaone.net >> >>For policy questions, send mail to: >> Richard Nute: ri...@ieee.org >> Jim Bacher: j.bac...@ieee.org >> >>All emc-pstc postings are archived and searchable on the web at: >> No longer online until our new server is brought online and >>the old messages are imported into the new server. >> >>
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