You are making the same argument Mr. Woodgate did, but adding another mechanism for creating the rf emission. Note that I did not offer an explanation of the source of an rf emission, I simply postulated its existence. Then I stated my point of departure from Mr. Woodgate's analysis, which was that even given an rf emission, I didn't believe that would be sufficient to interfere with a wired handset on a land line.
Mr. Woodgate subsequently humorously commented regarding my assertion (that this would be a more credible problem if the handset were a cordless link). And his comment was right on target. If that actually was the case, and it was not mentioned in the original posting, then Mr. Wan Juang Foo deserves 50 lashings with a wet noodle, or the proper cyberspace equivalent. The underlying point I was making was that it is not enough to have an rf emission, you have to have a victim sensitive enough to pick it up and respond. An rf emission even 30 dB over the limit should not cause problems except at a radio's tuned frequency, or to very sensitive instrumentation, such as you might have monitoring brain waves during surgery. And that last assumes an unintentional demodulation capability. > From: Cortland Richmond <72146....@compuserve.com> > Date: Sat, 26 Jul 2003 13:06:25 -0400 > To: Ken Javor <ken.ja...@emccompliance.com>, ieee pstc list > <emc-p...@ieee.org> > Subject: Re: self blinking LEDs as EMI sources WAS: LED lamps > > > Ken Javor wrote: > >>> ... but I wonder if the presence of even an rf emission (as contrasted > to 50 Hz) should cause any problem to a land-line phone with a wired > handset. It wouldn't seem likely that the > power available from a couple AA batteries would be sufficient for that. > Now if it were a cordless phone and there were an rf emission in band to > the cordless link, that would be much more credible. << > > > I'd lean towards a more prosaic explanation; oscillations involving the > transistors which make the LED's blink. During the inevitable time in a > linear region of operation while switching, they may well be oscillating at > frequencies determined by the length of the wires to which they are > connected. This would last only a short time, of course, but would generate > a narrow RF pulse which might well be rectified in a nearby audio > amplifier. > > Cortland > 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
