[time-nuts] How to measure regulator noise?

[Henk ten Pierick]

On Jan 8, 2008, at 12:50, Don Collie wrote:

> I`d just hang an AC millivoltmeter[or microvoltmeter] across the  
> regulator`s
> output.
> I use my H/P 400H, which will give readings down to about 50uV. If  
> your
> regulator produces less noise than this [say a 723, with
> 2uV], then you`ll need a more sensitive meter.

Electronic voltmeters or microvoltmeters have a noise bandwidth which  
is larger than the bandwidth on the front panel.  The front panel  
bandwidth is related to accuracy and is not the -3dB bandwidth. The  
noise bandwidth is nearly always range setting dependent and can vary  
very much. I have seen a factor of four in noise bandwidth between  
adjacent range settings. The only way to have a good indication on  
noise is in a known and constant bandwidth. The noise bandwidth of a  
filter is not the same as the 3dB bandwidth and dependent of the  
filter order and shape. It is always more.

Henk