If I assume that the top loaded antenna acts as a quarter wave stub, that is it is extremely efficient at radiating all the power presented at the base and not reflecting any back, and if I further assume this is CB band or higher (essentially at or above 30 MHz), then 600 Watts 5 meters away (one car length behind) yields 47 V/m (70 mA drive). If we assume a one meter separation (and ignore that we are in the near field and the scaling from 5 meters to one meter is incorrect in a worst case sort of way) then the field intensity is 235 V/m (350 mA drive). This might be the case if the cars were side-by-side. Further evidence that the 1 Amp BCI limit is too stringent.
on 1/10/02 1:30 PM, Cortland Richmond at [email protected] wrote: > A worst case -- "real world" -- is probably just behind a radio equipped car, > mounting a capacitively top-loaded > antenna at its rear edge, and about 600 watts of RF. > > With rather less power, 100 watts, I've occasionally seen adjacent cars' > engines stop when I transmit. It would be > interesting to see if RF at these levels got into electric cars' motor > controllers. > > Cortland - KA5S > > (What I write here is mine alone. > My employer does not > Concur, agree or else endorse > These words, their mood, or thought.) > > > Ken Javor wrote: > >> ... >> >> For the case in point, an automobile, I assume the longest cable 5 meters. >> Five meters is a half wavelength at 30 MHz. Personally I am not aware of >> any requirements in the automotive world above 200 V/m, but I may be wrong >> on that as I haven't done any automotive consulting in at least five years. >> Based on 200 V/m, the bulk current injection limit would be 300 mA or 110 >> dBuA above 30 MHz, decreasing 20 dB per decade with decreasing frequency >> below 30 MHz. This is very much a worst case coupling assumption, since 1.5 >> mA per Volt per meter depends on plane wave illumination of a cable 5 cm >> above ground with the magnetic component of the field penetrating the loop >> formed by the cable above ground at right angles over the entire length of >> the cable run. > ------------------------------------------- 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.
