[time-nuts] How to measure regulator noise?
didier at cox.net
Sun Jan 6 15:29:11 EST 2008
Have you looked at the voltage with a scope at the same time the analyzer is
Could the coupling capacitor be leaking ?
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] 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?
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