Hi Ken and the group, There are no resistors in the coupling network to make the source impedance 150 Ohms. Just the capacitors to couple the noise and series impedance to reduce the noise the noise fed back into the power line. The source impedance onto the power line is 50 Ohms.
The capacitive clamp is essentially a section of a 50 Ohm transmission line, but is not terminated when used, just left open on the end. Doug Ken Javor wrote: > As I said, I am not an expert on this test, but the CDNs used for 61000-4-6 > are built to provide 150 Ohm source impedance, assuming a 50 Ohm signal > source impedance. They do this by providing an additional 100 Ohm series > impedance between signal source and cable-under-test. I don't understand > why this would be a proper model for the 61000-4-6 test (field-to-cable > coupling) but not the EFT requirement. > > Also, if you used a 0.1 uF blocking cap, at 150 kHz that increases a 50 Ohm > source impedance to 51 Ohms, which is hardly a significant increase. At the > power frequency, 0.1 uF is 26.5 kOhms, which provides 54.5 dB of attenuation > protecting the signal source from the power line. That brings the power > frequency potential at the 50 Ohm signal source down to 226 mV (0 dBm) for a > 120 Vrms mains which should prevent harm. For a 220 Volt mains, the numbers > are 450 mV or 6 dBm, which also shouldn't cause harm. > > >>From: Doug Smith <[email protected]> >>Organization: D. C. Smith Consultants >>Reply-To: [email protected] >>Date: Sat, 13 Aug 2005 22:17:39 -0700 >>To: Ken Javor <[email protected]> >>Cc: EMC-PSTC - Forum <[email protected]> >>Subject: Re: Capacitive Clamp insertion loss >> >>Hi Ken and the group, >> >>Yes, the blocking caps are low impedance. But the generator is only 50 >>Ohms not 150 Ohms so the total source impedance is still about 50 Ohms >>including the blocking caps. >> >>Doug -- ___ _ Doug Smith \ / ) P.O. Box 1457 ========= Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: [email protected] \ _ / ] \ _ / Website: http://www.dsmith.org 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
