[RFI] New Larger Fair-Rite #31 Toroid

[Larry Benko]

Dave,

You might be surprised how accurate the following formula is:

Toroid effectiveness is proportional to
    permeability*log(OD/ID)*length

This is not an absolute number and it works for both donut and cylinder 
shapes so the units do not matter as long as you are consistent.  The 
larger toroids will allow larger diameter wires but will end up with a 
longer winding length reducing the self resonant frequency some.

Also this big #31 toroid is not new as I sampled some about 5 years ago 
and then bought 10 more directly from FairRite.  I have found over the 
years that they make many parts that are not in their catalog.

Larry, W0QE


On 3/26/2017 6:17 PM, Dave Cole wrote:
> Jim,
> What would you estimate the optimal number of turns to be for this 
> ferrite?
>
> 73s and thanks,
> Dave
> NK7Z
> http://www.nk7z.net
>
> On 03/26/2017 04:22 PM, Jim Brown wrote:
>> KY8D asked me about a new, larger #31 toroid that has recently been
>> added to the catalog. It's 4-in o.d., 3-in i.d, and 1-inch long.
>>
>> http://www.fair-rite.com/product/round-cable-emi-suppression-cores-2631814002/ 
>>
>>
>>
>> Note the impedance data for 1, 3, and 5 turns at the bottom of the page.
>>
>> Gan's email arrived today (Sunday) so I haven't had the opportunity yet
>> to investigate pricing. My guess is at least double the cost of the
>> 2.4-in toroid, but because it's twice the length (1-in as opposed to
>> 0.5-in for the 2.4-in toroid), a single core will likely be equivalent
>> to two of the 2.4-in cores, so fewer cores will be required to achieve
>> the same choking Z. More important, the much larger i.d. will allow more
>> turns and/or larger coax.
>>
>> 73, Jim K9YC
>>
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