[time-nuts] How to measure regulator noise?

Dave Brown tractorb at ihug.co.nz
Mon Jan 7 04:28:38 EST 2008

You won't need much of a cap for DC blocking as inputs are hi-Z....too 
big and the chargeup may well trigger the overrange condition.
Been a while since I used a 3561A but can't the input tolerate up to 5 
vdc? I may be thinking of something else.
Great instruments - wish I still had access to one.  There's a lot of 
good info in the support docs (not the 2 vol op-service manual) for 
the 3561A if you have any of that.

For this particular task maybe one of the high resolution (16 bit) USB 
scopes might be appropriate? (in FFT mode)

DaveB, NZ

----- Original Message ----- 
From: "John Ackermann N8UR" <jra at febo.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Monday, January 07, 2008 9:17 AM
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 
> 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
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