[time-nuts] The difficulty of low noise measurements

[Magnus Danielson]

Hi,

On 2020-01-11 18:57, Poul-Henning Kamp wrote:
> 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.
Mesh Bonding Network [1]
>
> 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].
Isolated Bonding Network [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].
Indeed. Then, being a ham, antennas is familiar to me. [2]
>
> I have on my ever-growing TODO list to test if serial-BLE adapters
> are any good.  Has anybody tried that yet ?
My recommendation is to build on the ESP32, then you can get serial port
to WiFi directly and the entry level price is small enough and there
exist a community of things. It is competent enough that you may let it
do some of the processing for you.
> 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.
The EFOS10 maser has UPS and batteries, sure they are not prime but I
can for shorter measurements just go and unplugg power if needed.
>
> For trivial loads, like the BVA, motorcycle batteries from "BilTema"

Indeed. I will setup a separate 24 V charger chain for the BVAs and a
few other things, as I want UPS for them too.

> 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].
I have a ham friend that is fairly well into batteries as he needs to
for his telecom installations.
>
> Poul-Henning
>
> [1] That's a fancy way of saying "no loops anywhere".
Indeed. I know that, but not all is familiar with the computer science term.
>
> [2] Note that the Maxim RS232 switched-capacitor level conveters
>     are noisy as hell, as are many USB-RS232 adapters.
I guess that is why I had two common mode chokes on the serial cable,
one at the USB adapter end and the other at the maser.
>
> [3] Or check if you can inherit at ton of OPzS from friends in
>     telecom, but pay attention to the hydrogen.
Good idea. It happens that we get these.

[1] ITU-T Rec. K.27 https://www.itu.int/rec/T-REC-K.27/en

[2] My club SK0UX http://sk0ux.se

Cheers,
Magnus