[RFI] New Larger Fair-Rite #31 Toroid

Jim Brown jim at audiosystemsgroup.com
Fri Apr 14 14:33:13 EDT 2017

On Fri,4/14/2017 10:26 AM, Dave Cole wrote:
> Jim,
> A question for you...  Looking at the "Impedance vs. Frequency vs. 
> Turn count" graph at:
> http://www.fair-rite.com/product/round-cable-emi-suppression-cores-2631814002/ 
> It looks like these new cores only have two or three K of impedance 
> with  five turns...  Am I interpreting this correctly?


> If so, then using two of them with five turns becomes the standard if 
> I want more than five K impedance?  Is that true?

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. A choke wound with RG8/11 size coax would have the 
same inductance but more capacitance between windings if those windings 
are closely spaced, so the resonance would be a bit lower.

And, of course, more turns will lower the resonance even more, and 
because R also increases with N-squared, also raise the impedance.

73, Jim K9YC

> 73s and thanks,
> Dave
> NK7Z
> http://www.nk7z.net
> On 04/14/2017 09:53 AM, Jim Brown wrote:
>> Yesterday, I got a quote on this part from Dexter, a vendor that has
>> been competitive for past orders. They don't have stock, minimum order
>> is a full box, which is 25 pieces, $15.18 each. 50 pieces is $14.27
>> (-6%). 100 pieces is $13.57. Delivery was quoted as 14 weeks.
>> 73, Jim K9YC
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