Hi Filtering *is* part of all this. If you are distributing a standard around the lab, cable management *will* be part of it as well. Having a volt p-p pop up due to an unterminated cable (of the right length) is not at all unheard of.
Bob > On Dec 24, 2019, at 3:48 PM, Taka Kamiya via time-nuts > <[email protected]> wrote: > > I just found something funny. I have been thinking "clean" power supplies > that connects to AC mains. Then I thought, what about lead acid batteries?? > So I went to my lab and took some measurement. This is a 12V 7A lead acid > sealed battery, the kind commonly found on UPS devices. > The result? Surprise? The battery is oscillating at 5MHz and noise level is > 15mV peak-to-peak!!!! > Of course, not...! Battery is pure DC and while voltage might drift, this is > not that. For the record, a charger of any kind is not hooked up. It's one > battery all by itself. Battery is not oscillating but that's what the > measurement actually shows. That brings another point in my quest to "clean" > power source. It's not just the power supply but the whole lab eco system > has to be considered. Having one master 24V source (my original plan) is not > the answer if mV level noise is going to be a problem. > > This "discovery" puts whole new layer to having a nice power supply..... > > Just as a point of reference, I hooked up a common cheap float charger. The > charger itself has 2V p-p noise. Connected to battery, it still have 100mV > p-p noise. There goes battery = noise sponge theory.... > --------------------------------------- > (Mr.) Taka Kamiya > KB4EMF / ex JF2DKG > > > On Tuesday, December 24, 2019, 3:00:50 PM EST, Bob kb8tq <[email protected]> > wrote: > > Hi > > >> On Dec 24, 2019, at 6:40 AM, Poul-Henning Kamp <[email protected]> wrote: >> >> -------- >> >>> That again depends on topology and control type. The canned converters >>> are almost always optimized to have the lowest number of switches and >>> work with cheap magnetics (single coil) without easily entering >>> problematic operation modes, noise is only a secondary concern. >> >> That depends a LOT on which canned converter you decide to buy, >> if you only go after price, or W/mm³ capacity, then certainly yes. >> >> But for a one-off application like this, any money saved on a >> cheap model is easily lost many times over in the trouble it will >> cause. >> >> But returning to the original post: Has anybody ever characterized >> how much difference it makes to use two different PSU's for heater >> vs. electronics sides of telecom Rb's ? > > The “old time” answer was that a poorly regulated / poorly filtered supply > was > considered “ok” for a heater. For the active electronics you wanted something > nice and stable / clean. To your point, once you get around to *measuring* > this, stability wise that answer often does not hold up. Noise wise, you are > right > back to “what frequency?” …. > > The somewhat more complex “old time” answer was that you don’t want the > honking big current of the heater coming off the supply you have tried so hard > to super-regulate. ( = it’s the supply that’s the issue not the Rb it’s > self). Obviously > that’s going to depend on how the supply was designed. > > Of course next layer to the onion is …. where does the ground current go? …. > hmm…. > > Bob > >> >> I'm sure there is a reason why they make it two different pins ? >> >> -- >> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >> [email protected] | TCP/IP since RFC 956 >> FreeBSD committer | BSD since 4.3-tahoe >> Never attribute to malice what can adequately be explained by incompetence. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
