John, Have you looked at the voltage with a scope at the same time the analyzer is running?
Could the coupling capacitor be leaking ? Didier > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of John Ackermann N8UR > Sent: Sunday, January 06, 2008 2:18 PM > To: Discussion of precise time and frequency measurement > Subject: [time-nuts] How to measure regulator noise? > > I'm experimenting with some low noise regulators, and want to > do some meaningful measurements to compare them (and > hopefully compare to published specs). > > I have an HP 3561A FFT analyzer, which can probably be beaten > these days by a sound card, but has the advantage of absolute > calibration and GPIB to dump data. I also have a very low > noise 40dB audio amplifier that covers <10 Hz to >100 kHz. > > I've tried just looking at the regulator output with the > analyzer, with and without the amp, but am not sure what I'm > seeing. In particular, even with a capacitor to block the > DC, the analyzer indicates "Overrange" at a reference level > below -5 or so dBV. That puts most of the noise spectrum > below the bottom of the screen. > > Any suggestions on an appropriate test configuration, and on > how to get readings that directly relate to the root-Hertz > value shown by regulator data sheets? > > Thanks, > > John > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, > go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.516 / Virus Database: 269.17.13/1211 - Release > Date: 1/6/2008 11:57 AM > > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.17.13/1211 - Release Date: 1/6/2008 11:57 AM _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.