[RFI] Bulk order source for Ferrite beads?

[Dave Cole (NK7Z)]

Larry,

Could you expand a bit on that...

I don't see where mix61 is a better choice over mix31 at HF, other than 
the curie point is substantially higher for 61, which allows you to heat 
it up more.

Yes with a 31 choke one would need higher impedance to keep heat down 
below the curie point, but so what, I want higher impedance in my 
chokes...  Why does that make 61 a better choice than 31?

Mix61 looks worse to me than 31 for HF, pretty much across the board... 
Help me understand you point here please...


73s and thanks,
Dave (NK7Z)
https://www.nk7z.net
Award Manger, 30MDG Grid Awards
ARRL Technical Specialist
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On 2/3/19 7:06 AM, Larry Benko wrote:
> Jim,
> 
> I respectfully disagree with your comment about 61 material cores not 
> being useful at HF.  For transmitting applications they are quite 
> valuable.  The low Q impedance provided by 31 materials is the go to 
> solution for receiving applications but at high power care must be taken 
> to ensure that the impedance is much higher than needed to keep the 31 
> material from overheating.  This is made even more difficult since the 
> common mode impedance in a circuit is unrelated to the differential mode 
> impedance and calculating what common mode current might flow through 
> the common mode choke is not easy to do.  Of course you can sneak up on 
> the problem by just making the choke and slowly increasing the power at 
> all frequencies you use and see if it gets too hot in your application. 
> Not very scientific but common mode circuits are elusive to understand 
> and simulate.
> 
> Larry, W0QE
> 
> On 2/2/2019 3:30 PM, Jim Brown wrote:
>> I also recommend Arrow, both for cost and service, especially for 
>> small quantity. It helps a lot that shipping is free for an order of 
>> $20 or more -- IF it's a web order for what's in stock.  I also got a 
>> very good price on 100 pieces of the 2.4-in o.d. #31 toroids.  Other 
>> good vendors are Lodestone Pacific, Dexter Magnetics, and the usual 
>> industrial electronics houses like Newark, Allied, Mouser, etc.
>>
>> Note also that there is currently a tariff on these parts, which are 
>> made in Fair-Rite's factory in China.
>>
>> BUT -- #61 cores are NOT of much use for RFI suppression below UHF, 
>> and they are a terrible choice for a common mode choke (often called a 
>> "current balun").
>>
>> 73, Jim K9YC
>>
>> On 2/2/2019 9:04 AM, Tom WA9WSJ via RFI wrote:
>>>   Hi John,
>>> I once bought some big cores from these guys,
>>> https://www.jpmsupply.com
>>>
>>> (FT140-61 ferrites). At that time, a little over a year ago, they 
>>> were the best prices I could find.
>>> They do have a couple other types. Maybe they can help you.
>>> Good luck!
>>> 73 Tom
>>>
>>>
>>>
>>>      On Saturday, February 2, 2019, 9:26:14 AM MST, John Altman 
>>> <wa4aip at gmail.com> wrote:
>>>     Which company is the best source for bulk bead orders?
>>>
>>> Tks,
>>> John
>>> WA4AIP
>>> ARRL Charter Life Member
>>>
>>>
>>> Sent from my iPad PRO
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