I read in !emc-pstc that don_borow...@selinc.com wrote (in <OF685C23FA.C efd2279-on88256c6f.006f0...@selinc.com>) about 'A Different Kind of EMC Problem' on Tue, 12 Nov 2002: > >I have three devices in my house that cause problems with AM radio band >reception, but not due to emissions, > >In each case, the device adds modulation to strong AM signals, synchronous >with the power line. > >The three devices are: 1. A stereo adaptor for a Beta VCR, 2. A dishwasher >with electronic controller, 3. An electric toothbrush charger. > >I can see a possible mechanism for the first two devices - the periodic >connecting and disconnecting at radio frequencies of two large metalic >structures via the power supply rectifier diodes. The power wiring is one >structure. For the VCR, the other structure is the cable TV wiring, and for >the dishwasher the pumbing is the other structure. The electric toothbrush >charger must do it all through the wiring. > >This is definitely modulation - the radio station having the worst >modulation goes off the air for about 1 second at dawn and dusk while they >change antenna pattern, and the interference goes away. It the problem were >emissions, the interference would be very audible with the radio station >off the air. > >I haven't had the time to try filtering the power line at the devices to >address the problem, but that is not what this posting is about. > >My question: Are there any regulatory standards that address modulation >interference like this? > This is a very unusual phenomenon. If it is the 'modulation hum' of tube receiver days, it is due to a lack of immunity in the receiver. Have you tried other radios?
IIRC, h.f. noise generated by rectifiers and thus deeply modulated at power frequency gets on to the mains supply and, due to inadequate filtering or some capacitive coupling in the receiver, gets on to the local oscillator supply or the a.g.c. line. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! ------------------------------------------- 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: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
