[time-nuts] The difficulty of low noise measurements

[Poul-Henning Kamp]

At that level of the dungeon, you have a choice.

You can either bolt *everything*, including the chair you sit on
and the pencil you write with, together with copperstraps to get a
common potential.

Or you can arrange *all* your cables and other metalic connections
(cabinets touching because the insulating legs were lost years ago?)
to form a Directed Acyclic Graph[1].

Many people overlook that if you run 2 m cable to an opto isolator
you still have a 2m antenna.  It may no longer bother you in terms
of EMC, but it can still bother you in terms of EMI[2].

I have on my ever-growing TODO list to test if serial-BLE adapters
are any good.  Has anybody tried that yet ?

But foremost:  Use individual float-charged lead-acid for power-supplies.
so that you can unplug from the grid when you *really* want to
measure.

For trivial loads, like the BVA, motorcycle batteries from "BilTema"
are fine, but for larger capacity batteries you get what you pay
for, so contact somebody who knows what they are selling and will
not send you batteries which has been sitting on some shelf for 3
years[3].

Poul-Henning

[1] That's a fancy way of saying "no loops anywhere".

[2] Note that the Maxim RS232 switched-capacitor level conveters
    are noisy as hell, as are many USB-RS232 adapters.

[3] Or check if you can inherit at ton of OPzS from friends in
    telecom, but pay attention to the hydrogen.

-- 
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