What size ferrite ring do you use?
I use a small ferrite bead, I believe it is about 1/2″ inside diameter. It is the smallest one that I could find that still fits a servo lead through it. I can get about 2 wraps per lead on it.
I have them in stock here:
http://quadquestions.com/product/ferrite-bead-for-lc-filter-or-esc/
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