Hi All, Most of us use active probes because we believe they have a high input impedance. However this is not usually the case in the upper octave of their stated frequency range. My Technical Tidbit article for August, 2002 (http://emcesd.com) presents measured data on a popular active probe typical of most on the market. You may be surprised at the result. I also give an example of a good active probe that has reasonable input impedance and response over its stated frequency range in real measurement situations. Its instruction manual also gives good equivalent circuits and other data necessary to use an active probe properly. Two upcoming seminars you may be interested in that I am teaching: EMC: http://www.elliottlabs.com/services/seminars/emct_081802.htm High frequency measurement, design, and troubleshooting: http://emcesd.com/seminars/tolh0902.htm Both include many realtime experiments to illustrate the concepts being discussed. 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: doug@xxxxxxxxxx \ _ / ] \ _ / Website: http://www.dsmith.org ----------------------------------------------------------- ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu