I was not arguing that PEDS should be allowed to operate throughout ascent and descent. I was responding to Woodgate's comment that if PEDS are causing a problem, there must be serious immunity issues with aircraft avionics. I know in detail what the immunity requirements are, and I know that PEDS do not emit anywhere near the immunity levels. PEDS interfere with radio reception. Woodgate quite correctly pointed out that unless the rfi occurred at the radio tuned frequency, it can be considered an antenna port immunity concern, because immunity requirements can and are levied to protect radio receiver out-of-band sensitivity.
---------- >From: Warren Birmingham <[email protected]> >To: Ken Javor <[email protected]> >Cc: [email protected] >Subject: Re: New EU regulations - civil aviation >Date: Mon, Sep 16, 2002, 4:01 PM > > Ken, you may be right but it is like trying to convince the FAA that > there is no harm in using car gas in airplanes. There are just too > many ways for uncontrolled fuel to become contaminated from unknown > sources. > > With respect to the EMC and immunity issues, it is not the technical > issues that are of concern, but rather the liability and publicity of > even being accused of causing interference, regardless of how it got > there. The potential for it exists, and lives are potentially at > stake. Who would argue with this? > > I am also an aviation consultant as well as an engineering one. Most > devices are allowed to be used in flight. Cell Phones and 2-way pagers > cause too much GROUND interference when used from the air and THAT is > the primary reason they are not permitted. They use more resources > than intended when used from the air. > > By the way, I was consulting to a company that did not even test ANY of > their equipment to FCC Part 15, and I discovered that they were out of > specification for Class A by several db. We had our attorney negotiate > with the FCC, who wanted to know if ANY of the over-limit frequencies > fell into the aviation bands. They did not, so we had to fix the > problems with no other action required other than submission of new > compliant verification reports. There is concern for this even > originating outside of the aircraft. > > Warren Birmingham > Epsilon-Mu Consultants > (510) 793-4806 > email: [email protected] > website: http://www.epsilon-mu.com > > > On Monday, Sep 16, 2002, at 09:56 US/Pacific, Ken Javor wrote: > >> >> Most of what you say below meshes with my experience and does not >> contradict >> my basic premise, that PEDs can only interfere through aircraft >> antennas. I >> am curious what the resolution of the Boeing installation was. >> Equipment >> undergoing EMI qualification must be tested with a representative >> flight >> harness. Did your company test with screened cables and then try to >> force >> Boeing to use the same? Bad form. Did Boeing try to buy an >> off-the-shelf >> system qualified with screened cables and then install the system using >> unscreened cables? Equally bad form. This must be worked out before >> design >> and testing for procured equipment, and if the equipment is >> off-the-shelf, >> then the qualification configuration harness must be installed, or the >> equipment must be requalified using the planned/existing configuration >> wiring. Another question of interest: Was the system you provided >> Boeing >> flight critical? >> >> There is one place that what you say could be interpreted to imply >> that PED >> emissions get into aircraft wiring: >> >> "It has been found through surveys carried out on aircraft by ERA and >> QinetiQ that the interference appears to get into these systems from >> certain >> locations within the aircraft where cable run reside under certain >> seats." >> >> Consider the physical parameters. The PED is small and low power and >> while >> it may not meet RTCA/DO-160, it does not blanket the entire aircraft >> with >> emissions. The intensity falls off rapidly with separation from the >> source. >> This is clearly a case where the emitting device is electrically small >> over >> almost the entire communications band. >> >> Assume the emitted radiation intensity were 100 mV/m, 5-6 orders of >> magnitude above CISPR limits. The transfer function of coupled >> current to a >> cable above ground is 1.5 mA per Volt/meter. I can supply that >> derivation >> if you like, but it is inherent in both RTCA/DO-160D and >> MIL-STD-461D/E. It >> is different in IEC 61000-4-6, but that is because the ground plane is >> far >> away or nonexistent in buildings and the cable-under-test is a more >> efficient pick-up device in that environment. Anyway, the coupled >> current >> would be 150 uA, and that assumes at least one half wavelength of the >> cable >> was immersed in a plane wave with precisely the right orientation >> relative >> to the wire in order to get that. If the "victim" circuit contains >> information represented by low potentials, such as below 0.1 Volt, >> then I >> would expect the cable carrying that signal to be shielded, as in a >> twisted >> shielded pair. 150 uA riding on a shield should not cause any >> problems to >> any flight critical signal, even with a pigtailed shield termination. >> For >> instance, if the pigtail termination yielded a transfer impedance as >> high as >> 50 Ohms at some frequency, the resultant common mode coupling to the >> interior pair would still only be 7.5 mV. Again I contend that Boeing >> and >> Airbus would not route a flight critical signal with a threshold of >> susceptibility that low. And if the circuit is totally unshielded, >> that >> implies it is a discrete or other relatively high level signal, where >> information is carried in such a away that it takes Volts of induced >> potential to cause an upset. Coupling to an unshielded wire above >> ground >> occurs at a transfer function of 75 mV per Volt/meter. [ Cf. IEC >> 61000-4-6, >> coupling efficiency of 1 Volt per Volt/meter, open circuit from a 150 >> Ohm >> source impedance.] Given the original 100 mV/m assumption, that >> translates >> into a coupled common mode potential of 7.5 mV and the conclusion still >> stands: no possibility of interference. >> >> ---------- >>> From: [email protected] >>> To: [email protected] >>> Subject: Re: New EU regulations - civil aviation >>> Date: Mon, Sep 16, 2002, 8:55 AM >>> >> >>> >>> Ken >>> >>> During the mid 90s we manufactured equipment that was installed on >>> 747s >>> which was tested to RTCA/DO-160C and all the cables on that aircraft >>> for >>> that system were unscreened. Boeing informed us that they would not >>> permit >>> screened cables due to the increase in weight that would then affect >>> the >>> passenger cargo carrying capability of the aircraft. >>> >>> I know that rf signals are coax and that certain control signals are >>> screened for flight critical systems. >>> >>> It isn't so bad for newer aircraft but some of the older ones that >>> use Omega >>> and the earlier flight nav systems have reported interfernce with >>> these >>> systems and the autopilot. When the passengers have been requested to >>> switch >>> off their equipments the interference has dissappeared. >>> >>> It has been found through surveys carried out on aircraft by ERA and >>> QinetiQ >>> that the interfernce appears to get into these systems from certain >>> locations within the aircraft where cable run reside under certain >>> seats. >>> >>> Incidents of interfernce breakthough on coms have been more difficult >>> to >>> identify. Investigations are still being carried out. >>> >>> If you want more data suggest you get in touch wuth Dr Nigel Carter @ >>> QinetiQ or Eric Stevens @ ERA. >>> >>> Regards >>> Andy >>> >>> Andrew Price >>> Principal Development Engineer (EMC Specialist) >>> BAE SYSTEMS Avionics >>> A125 >>> Christopher Martin Road >>> Basildon, Essex >>> SS14 3EL >>> >>> tel: +44 (0) 1268 883308 >>> email: [email protected] >>> >>> >>> >>> ********************************************************************** >>> ***** >>> >>> This email and any attachments are confidential to the intended >>> recipient and may also be privileged. If you are not the intended >>> recipient please delete it from your system and notify the sender. >>> You should not copy it or use it for any purpose nor disclose or >>> distribute its contents to any other person. >>> >>> ********************************************************************** >>> ***** >>> >>> ------------------------------------------- >>> 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: >>> [email protected] >>> with the single line: >>> unsubscribe emc-pstc >>> >>> For help, send mail to the list administrators: >>> Ron Pickard: [email protected] >>> Dave Heald: [email protected] >>> >>> For policy questions, send mail to: >>> Richard Nute: [email protected] >>> Jim Bacher: [email protected] >>> >>> All emc-pstc postings are archived and searchable on the web at: >>> http://ieeepstc.mindcruiser.com/ >>> Click on "browse" and then "emc-pstc mailing list" >>> >> >> ------------------------------------------- >> 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: >> [email protected] >> with the single line: >> unsubscribe emc-pstc >> >> For help, send mail to the list administrators: >> Ron Pickard: [email protected] >> Dave Heald: [email protected] >> >> For policy questions, send mail to: >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >> All emc-pstc postings are archived and searchable on the web at: >> http://ieeepstc.mindcruiser.com/ >> Click on "browse" and then "emc-pstc mailing list" >> >> > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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