[time-nuts] How to measure regulator noise?

[John Ackermann N8UR]

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