Amund The common solution to this problem is to wind about seven turns of the telephone cable on to a large ferrite ring of about 75mm diameter. Not very elegant, but it works over wide frequency range and down to at least 27 MHz. Keep the ferrite close to the phone and do not overlap the turns.
I used this once on a phone that was the victim of a diathermy machine at high field strengths and it worked a treat. It also does not violate the approvals on the phone. If the interferer is at a higher frequency then a couple of clamp on ferrites might work. John McAuley Compliance Engineering Ireland Ltd www.cei.ie From: [email protected] [mailto:[email protected]] On Behalf Of Amund Westin Sent: 29 August 2005 05:45 To: [email protected] Subject: Analog telephone - RF field susceptible Many analog telephones are susceptible to radiated fields. It's easy to observe audible noise (the sine 1kHz modulation tone)when RF fields are introduced under a laboratory test (IEC61000-4-3). Do you have any good EMC design techniques which improve the resistance to such RF fields, when the telephone enlosure is plastic material and wire is unshielded? Thanks. Best regards Amund Westin This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [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: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [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: http://www.ieeecommunities.org/emc-pstc
