How to build your a common mode noise choke with common ferrite cores

Paul Cianciolo

Hi Folks 
I had a lot of questions and requests about the common mode noise choke video I did previously.
It seemed like the thing to do was to make another video showing what components are needed, where to buy them and how the new choke compares with the original.

Here is the link to the video.
Le me know if you have any questions.



Kriss Kliegle

I found these on my 'go to' shopping source:

22mm O.D. x 14mm I.D. x 6.5mm (0.86"O.D. x 0.54"I.D. x 0.26"). Charcoal color.

Apparently a FT-87 W mix per a reviewer, stating the following:


Reviewer: A viewer from LK FOREST PK, WA USA

This is an FT-87-W. I got 27.9 mH from 60 turns of #24 wire.
See <>

   Magnetics, Inc says "W material is a high permeability material used for EMI/RMI suppression, common mode chokes, pulse and broadband transformers." They might be a bit lossy in a switched mode power supply, but I think they would make nice audio filter inductors, if you don't mind winding a zillion turns on a smallish toroid. Amidon sells them for $1.20 apiece.

I had to look up the W mix since I'm not familiar with lettered mixes found:

W Material

W material is a high permeability material used for EMI/RMI suppression, common mode chokes, pulse and broadband transformers. Available in shapes and toroids.


Initial Perm (10 kHz) 10,000 ± 30%
Saturation Flux Density (3,900 G at 15 Oe, 25°C) 390 mT, 11.9 A•T/cm
Curie Temperature 135°C
Maximum Usable Frequency (50% roll-off)  ≤0.5 MHz 
Relative Loss Factor (tan δ/µiac) X10-6, 25°C  <7 (10 kHz) 
Remanence (800 G, 25°C)   80 mT 
Resistivity   0.1 Ω-m
Density  4.9 g/cm

Would this be usable in your filter as shown in the above video?

I actually heard WWVB for the first time yesterday on an end fed wire of 124' at +100' AGL. Not as noisy as your site was before filtering, but there are artifacts in the band I'd like to remove.

73 Kriss KA1GJU


I think that core should be fine for anything below 1Mhz as an EMI/RFI choke. For frequencies at or above 1Mhz you would probably use type 31 or 43 material. Possibly even type 75 in my experience with just transformers for amplifiers.