Look closely... this is NOT a screened coax cable
Why dose it matter here and or for this argument?
Are you saying it would be something different if it would be a coaxial wire? An ideal Bifilar Wire with conductors close together wold work the same way.
Also I have said many times a ferrite works for common mode RF.
so it is a common mode choke?
It does not work for differential mode.
Like a Ideal common mode choke... that's the point of an common mode choke high impedance in common mode, low impedance in differential mode.
The info is there. There is nothing mysterious about it. Books and webpages have been written about it.
And all of them seem to conclude a bifilliar or coaxial bifillar common mode choke with one turn is still a common mode choke.
Never saw someone stating any different.
Anyways you seem to accept that they (both) add impedance in common mode and and thereby they can reduce common mode (RF) curret!
Kirchhoff's current law tells us there need to be some sort of a loop for current to flow.
(HF-RF current can kind of "jump" trough the air a fair bit...)
On Parth this (RF) current can flow is trough the (Mains) Ground (or something else)
But in the case it dose and the Common mode current loops goes over ground i call it a
Ground loop.
Is that not a ground loop for you? if not how would you call it?
No matter how you want to call them... Filters (i refer to as common mode choke) that can reduce common mode currents exist. they are widely used in industry's
USB devices that emit common mode currents also exist.
USB DACs susceptible to common mode currents also exist.
is the tested device a common mode choke? NO. can it reduce common mode currents? NO. dose it improved the audio? NO
Dose it proof all common mode choke/filter are useless snake oil. also no.
If you want to test a water filter you would not do it with clean water, would you?
If you don't have clean water (coming from you USB port) you shuld check why and if your DAC can't handle a litte bit dirt on its in put you schuld get one that can.