[time-nuts] Power supply for time source concerns

[Bob kb8tq]

Hi


> On Dec 24, 2019, at 6:40 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> 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
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
> 
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