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 <[email protected]> >To: [email protected] >Subject: Re: EMC-related safety issues >Date: Tue, Jan 1, 2002, 2:17 AM > > > I read in !emc-pstc that Ken Javor <[email protected]> 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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [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: > 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [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: No longer online until our new server is brought online and the old messages are imported into the new server.
