I read in !emc-pstc that Cortland Richmond <[email protected] m> wrote (in <[email protected]>) about 'EMC-related safety issues', on Mon, 14 Jan 2002: >A loop can indeed radiate harmonics, if it is a reasonable fraction of a >wavelength long. A very small loop, tuned to >resonance by some capacitance, is less likely to do so.
The structure described by Keith is not a conventional loop and is small compared with a wavelength of 200 MHz: QUOTE The large PCB on which the HCMOS hex inverter was located had a 0.5 inch wide ground and power trace running all around its perimeter, one on each side of the two-layer PCB. Thin traces ran from these 'power buses' to all the ICs on the PCB. The dimensions of the perimeter traces were perfectly right for resonance at 200MHz (and there were no decouplers between the traces) and they made a wonderful rectangular frame antenna at that frequency too. The HCMOS device that suffered the unterminated gate was in the centre of the PCB and got its +5V from the trace at the top of the PCB, its 0V from the trace at the bottom, thereby making an excellent driver for the resonant circuit. The end result was a high-Q resonant 'tank' circuit being driven by the hard-switching device, and setting the basic oscillation frequency. Because the device was hard switching, it didn't heat up. Because the tank circuit had such high-Q and was also a great antenna it radiated the 200MHz component but not the other harmonics of the hard switching device. UNQUOTE I don't necessarily agree with everything in the above, but the ground and power traces are inductors (you could say, 'two inductors in parallel' in view of the geometrically symmetrical drive configuration) and the capacitance between them has the board as dielectric. -- 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.
