[time-nuts] Power supply help

[Magnus Danielson]

Joseph Gray wrote:
>> A good test would be to load it down to its rated current and voltage
>> and monitor noise with a clamp on current probe ( on one lead)
>> to a low frequency spectrum analyzer
> 
> I don't have a spectrum analyzer. I emailed a friend about using his.
> 
>> Open it up and look for tell tale signs of the original equipment
>> manufacturer, possibly on the PCB.
> 
> I don't find any vendor markings on the boards that I can see. The
> main switching circuit is housed inside a metal box that would be
> difficult to take apart. The entire assembly is built into another
> metal box that has a removable top. Everything seems well shielded.
> 
> I did do a test last night, using my Sony ICF-2010 shortwave receiver.
> I can't power the Sony directly from the 13.8VDC, but I did plug its
> power adapter into the same AC socket as the HP supply. With the Sony
> sitting on top of the supply, I didn't notice any noise from the
> supply on 80M-10M. I thought I heard some noise on 160M, but that band
> was so noisy that it was hard to tell.
> 
> If my friend with the spectrum analyzer comes through, I'll be able to
> see some real measurements on the DC output itself.

Make sure that it survives the 13.8 V DC (or whatever it hits on the 
scope as maximum). Chanses are it doesn't, so a DC blocker or a 
resistive divider may be needed to make the DC levels within acceptable 
range. DC blocker acts like an highpass filter, so beware of the cut-off 
frequency while the divider will damp all signals, so be sure to include 
that in any level measurements if you want anything near absolute values.

Cheers,
Magnus