[time-nuts] SMPS or conventional?

[Tom Van Baak]

 > Planning to build my "reference box" with a rubidium & a gpsdo.

I went through this power supply decision making process with my first 
OCXO and Rb standards. In the end my conclusions are "if you can't 
measure it then don't worry about it". You can see how that leads to a 
side hobby of noise measurement!

There are any number of subtle decisions with operating a precision 
standard at home. This creates widely varying conditions from one 
person's shack to another person's lab. So for me a universal rule is 
difficult. In addition often the better the standard the more it is 
designed to attenuate external effects like variations in temperature, 
wander in supply voltage, or noise on any of the inputs.

I used to use high quality linear power supplies only. Now I usually use 
switchers. Part of it is that switching technology has progressed well 
over the decades. Part of it is that I can now make incredibly precise 
measurements and if the power supply gives me any PN spurs or any ADEV 
effects, I avoid it. Surprisingly some of the cleanest power supplies 
I've used are $15 switcher desktop or wall wart types. So that's what I 
often use now. If you have a DMM or 'scope or SA put it to use on the 
power supply itself or on the frequency standard output and see what you 
can find.

The other lesson I learned is to keep batteries and AC power supplies 
out of the box if possible. Use the box to hold the OCXO / Rb: for 
mechanical stability, for protection, for RF shielding, and for passive 
thermal management. Give it DC, and make the decision on where to get 
that DC independent of the box you're making. This also makes it much 
easier to implement clean or redundant power to the box. My worst 
experiences are battery chargers inside the box itself. That's too 
chemical, erratic, and noisy an operation to be in close proximity of a 
precision standard. Plus it's a maintenance hassle every few years when 
you have to replace the battery. I also avoid fans if I can. YMMV. These 
are just some of the things I've run into.

/tvb


On 10/19/2020 7:24 AM, Luiz Alberto Saba wrote:
> Hi guys
>
> Planning to build my "reference box" with a rubidium & a gpsdo.
> SMPS will do a good job or the transformer+bridge+capacitor+regulator 
> is best suited for this application?
> In the "test phase" I've used a switched ps for the rubidium and a 
> conventional for the gpsdo.
>
> Thanks
>
> Luiz Alberto Saba
>
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