A quick note to clarify the need for ferrite rings...
The ferrite ring acts as a common-mode, inductive filter of the high-frequency noise produced by the switching of the converters inside of the ESC. Basically, it prevents the current fluctuations inherent in ESC switching from progressing beyond the ring itself, thus eliminating the potential for making your ESC signal wire an antenna that radiates at the frequency of the common-mode noise. It also prevents that noise from getting into your receiver or servo signal wires.
This noise can adversely affect signal transmission in the lower-frequency bands that were used in older radio systems, but 2.4GHz is pretty robust to the frequencies produced by ESC switching. That having been said, it's not a bad idea to keep the ring in place when an ESC company provides it. It will never hurt the system, only help or do nothing...
In the case of the Kontronik, it is still capable of noise production on the signal wire because it is not optically isolated like a lot of other HV ESC's. Optical isolation prevents noise from being transmitted, but also prevents power from being transmitted too...thus, no opto-isolated ESC's have BEC's in them. Scorpion and Castle HV ESC's are optically-isolated and as such either don't come with ferrite rings (Scorpion) or, if they do (some Castles), are simply taking advantage of universal parts in their various product lines rather than having different wires for each ESC.
Hopefully this helps dispel the "hand-waving" and "magic" quite frequently surrounding ferrite rings...
Cheers,
-->J
