[time-nuts] The difficulty of low noise measurements
jimlux
jimlux at earthlink.net
Sat Jan 11 19:01:50 UTC 2020
On 1/11/20 9:57 AM, 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.
>
> 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].
Two theoretically isolated 2m tall, 1m deep racks separated by 1cm is a
2nF capacitor. At 10 MHz, that's a not so huge series 9 ohms in your DAG.
> I have on my ever-growing TODO list to test if serial-BLE adapters
> are any good. Has anybody tried that yet ?
That is an interesting idea. I wonder if you could make a short distance
fiber connection by just having your notional 10MHz source directly
drive the diode, with maybe a series resistor (so you don't need a power
supply). You could almost certainly do this for an RS232 output. I
wonder if there's a "no power required" approach for the receiving end.
or a low noise RS232-fiber adapter that steals power for the Rx side by
using the Tx signals. No level shifters and charge pumps.
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