Making low-noise measurements can be hard! Sometimes, if the device-under-test is small, I try to place it inside a shielded enclosure. There are some (+) Ideas on Building a Shielded Test Enclosure - element14 Community here.
There was a recent discussion concerning noise with an amplifier module setup which involved USB power and an audio signal from a PC. I tried to replicate it, and one of the experiments involved using a common-mode choke component, wired into the supply connections.
When working with cables, it’s possible to use ferrite cores as a common-mode choke too; that's the bulky thing often seen on USB cables for instance.
I recently tried to measure the noise on a power supply, and shot a quick video (with handheld mobile phone otherwise I would never have got around to a proper recording; sorry for the poor quality) showing my attempts to reduce noise pick-up from the environment.
While I managed to get the noise low enough that I could proceed with my end measurements, I’m not going to suggest this is best practise (I could have put more thought into using an actual 'scope probe, or considered a 50-ohm termination measurement perhaps with a capacitor to remove the DC component. Plus, the cable I used doesn’t have a controlled impedance for instance, and the measurement may only be usable for a few tens of MHz), but, I thought it may be interesting to share the video anyway, since it shows some of the considerations I had to make (such as powering off lights/equipment nearby to reduce pickup).
If you have any tips/tricks, or encountered interesting noise related issues, please share them!
