[RFI] Good guess as to type of ferrite?

Jim Brown jim at audiosystemsgroup.com
Wed Dec 18 02:20:28 EST 2013

On 12/17/2013 9:48 PM, David Cole wrote:
> They mostly use Mix43 on monitors...

Or a mix with a similar spec by another mfr. As has been noted, Part 15 
compliance essentially starts at 30 MHz.  OTOH, a single turn on #43 
(one pass through the core) is predominantly inductive below about 75 MHz.

As noted in my RFI tutorial, resistive choking Z is the most useful, 
because it cannot be resonated by the antenna behavior of the line it's 
choking. This was known at least as far back as the 1950s -- when 
researching for my AES paper on the topic, I found applications advice 
from that time frame making that clear -- but somehow that knowledge 
died with the retirement of the RFI practitioners of that era. By the 
time I found those references, I had already come to that conclusion on 
my own.

73, Jim K9YC

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