This is a repost as an image in Tim's original mail cause my reply to bounce. I have removed the offending gif from Tim's message:
Subject: Re: Reverse AliasingRe: scope probe gnd From: Douglas Smith <[email protected]> <mailto:[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Tue, 10 Mar 2009 20:30:59 -0700 To: Wan Juang Foo <[email protected]> <mailto:[email protected]> CC: [email protected], "[email protected]" <mailto:[email protected]> <[email protected]> <mailto:[email protected]> Hi Tim, The serpentine zig-zag folding will only be effective at frequencies where the zig-zag is physically small with respect to a wavelength. At higher frequencies (several tens of megahertz) the folding will create resonances of its own. Rather, I prefer putting several lossy ferrite cores on the scope cable in different locations including at the scope chassis and at the probe end of the cable. Doug Wan Juang Foo wrote: I like the suggestion of tieing the 2 probe cable into a hardness for mostof the way because it will reduce DM currents from being induced in the ground loop. Folding and ing the excess lengthe of that pair of probe cable in a serpentine zig-zag and locating the scope near to the point of measurement will help. One thing to add, recent years there was a proliferation of DSOs (Digital Storage Oscilloscopes) in the market. These are very nifty things when it comes to the bells and whistles, they made very good real time analysers. The thing to watch out for is that some of them had automatic changes in sampling rates as we reduces the timebase. A form of reverse aliasing can be a real problem if we are tying to sample a very slow changing event. sincerely Tim Foo <http://www.geocities.com/timfoo6143/> -- ___ _ 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] \ _ / ] \ _ / Web: http://www.dsmith.org - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/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: Jim Bacher <[email protected]> David Heald <[email protected]>
