I read in !emc-pstc that Ken Javor <[email protected]> wrote (in <b85e7016.c59%[email protected]>) about 'EMC-related safety issues', on Sun, 6 Jan 2002: > Quote : "Who would have expected an unterminated HCMOS gate to be > able to emit 2W at 200MHz?" > > Not me - 2 Watts of effective radiated power implies over 2.5 V/m > at 3 m! I guess I have a hard time believing that was transmitted > from an HCMOS gate. I think a little common sense will go a long > way towards retiring some of these EMC-urban legends. > > on 1/6/02 10:40 AM, [email protected] at [email protected] > wrote: > >> A.2) A portable computing device used in an automatic change machine >> on >> board transport was tested to be fully compliant with EN 55022 (approx >> = >> CISPR 22). >> I helped the manufacturer investigate complaints of interference and >> discovered that sub-fitted variant, which had not been tested for EMC >> compliance, left an HCMOS inverter IC with an unterminated inverter - >> which promptly decided to self-oscillate at 200MHz. (Many >> manufacturers >> of products with a number of build variants only test the fully-loaded >> one for EMCD compliance and assume the others are at least as good.) > >> The very interesting thing about this example is that the power-ground >> structure of the PCB made a beautifully tuned antenna and resonant >> circuit at 200MHz, so although the inverter was hard-switching and did >> not run hot, the only emissions were at the 200MHz fundamental - no >> harmonics were emitted at all. > >> Another very interesting thing is that some of the complainants had >> measured the equivalent radiated RF power from these devices as 2W. > Who would have expected an unterminated HCMOS gate to be able to emit 2W > at > 200MHz?
Indeed, and assuming a 5 V supply, the current would be around 400 mA. At 200 MHz, the dissipation would be several hundred milliwatts. The absence of harmonics even suggests that this gate was producing a sine-wave, which makes the figures even higher and less credible. -- 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.
