[RFI] New Larger Fair-Rite #31 Toroid

Jim Brown jim at audiosystemsgroup.com
Fri Apr 14 16:39:29 EDT 2017

I mean two chokes, each with five turns, wound on the same coax. There 
is a HUGE difference. Study k9yc.com/RFI-Ham.pdf, which includes a 
tutorial on how ferrite chokes work.

The chokes in series keep the same resonant frequency (and the broad 
resonant peak is the range where they work as chokes). Winding only one 
choke on two cores lowers the resonant frequency by the square root of 
2, because there's twice as much L. and Fr varies as the square root of 

73, Jim K9YC

On Fri,4/14/2017 12:27 PM, Chuck Gooden wrote:
> Jim,
> Could you clarify if you mean 5 turns through each core as in separate 
> chokes in series.  Or 5 turns through both cores as in 1 choke with 
> two cores? Or is there a difference?  It doesn't seem like there would 
> be a difference.
> Chuck K9LC
> On 4/14/2017 1:33 PM, Jim Brown wrote:
>> The number of turns (and to to the extent that it affects 
>> capacitance, wire size and spacing) sets the resonant frequency. The 
>> Fair-Rite data is most likely for small diameter wire. If you want 
>> the choke to be effective where 5 turns puts it, yes, two chokes in 
>> series would be the way to get there.
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