[RFI] Material 75 vs Material 31 Ferrites for EMI

Jim Brown jim at audiosystemsgroup.com
Fri Feb 10 17:42:20 EST 2017


Chuck,

I looked into this half a year ago when someone asked the same question. 
The answer was no. I don't remember why.

Study my material on this topic. Below 5 MHz, we need multiple turns 
through a #31 core. Between 5 MHz and 6M, we need multiple turns through 
#31 or #43.

Clamp-ons of either are a waste of money and do nothing at HF.

73, Jim K9YC

  On Fri,2/10/2017 12:10 PM, Chuck Gooden wrote:
>
> Fair-Rite has introduced a new low frequency material (#75), I was 
> wondering if someone could comment if this new material would be 
> better that #31 for EMI suppression.
> According to the Fair-rite web site, #75 shows a higher impedance at 
> lower frequencies than #31 but above ~2 Mhz the impedance drops off.  
> While the impedance of #31 seems to continue to increase and the 
> frequency goes up.
>
> I am planning on ordering some snap-it cores  to reduce the noise from 
> switch mode power supplies, and other sources, I am experiencing on HF 
> bands.  I have already read the documents on the K9YC web site but 
> there was no info on the new material.  I am tempted to stay with #31 
> due to it's long time use.
>
> Thanks,
>
> Chuck K9LC
>
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