NEW PRODUCT: 311400 fits larger cable 1"3/8 diameter. Call us for ordering.

Immunize your entire house and office with our ferrite cores!

They come in 2 split-ferrite halves, in plastic case. So you can clamp them on any cable assembly. Split ferrite cores make your job easy in the real world! Cables usually come with connectors of some kind or other. Ferrite cores are also available as solid cores, but in that case you may have to take connectors off before you can put them on the cable. Ferrite cores work bi-directionally. They suppress offending radiation as well as attenuate unwanted noise on a received signal. Place a ferrite core on a cable as close as practical (ideally within an inch or two) to the equipment to be protected. If you want to protect equipments at both ends of cables, place ferrite cores at both ends.

For general applications, put one on one cable. For near by RF presence applications such as amateur radio, use at least a few ferrite cores or make a loop or few, whichever is practical.

Made in the U.S.A.

RoHS compliant.

Ferrite 31500

Price: $4.45

Ferrite 311000

Price: $17.95


Click on Installation on the bottom of the following applications for installation pics.

Home Electronics


Ham Radio



31 Material: A new MnZn ferrite designed and manufactured by Fair Rite specifically for EMI suppression application. For EMI/RFI suppression applications, 73, 75 or 77 materials are generally used for 1-30 MHz. 43, 44 materials are generally used for 20-250 MHz. 61or 64 materials are used for 200 MHz or higher. 31 material covers a very broad frequency range of 1-1,000 MHz, truly the best overall material.

Physical Dimensions: inches (millimeters)

Part# Fitting Cable "B" Diameter (max)

Outer Diameter "A"

Length "C"

Impedance w/no loop(ohms)


.514 (13.05)

1.220 (31.0)

1.55 (39.4)

260 max

311000 1.010 (25.65) 2.220 (56.4) 1.69 (42.95)

375 max

311400 *


1.465 (37.2) 2.445 (62.1) 2.50 (63.50)

530 max

The plastic case is polypropylene (black) and has a flammability rating of UL94-V0.

* 311400: It comes in two half split cores without a plastic case. Use a cable tie or a vinyl electrical tape (not supplied) to assemble them. 311400 is $39.95 each. You will receive a pair of two halves per each order.


If there is a slack in the cable, just wind a few turns of the cable around the ferrite core. This is the best way to increase suppression strength. For example, just one loop to make 2 turns result in 4 times the original impedance thus quadrupling the suppressing strength. Make it tight and even spread windings for best results.

[(Original impedance) ohms x (Square of number of turns) = (New impedance) ohms]

This equation becomes less valid as frequency increases. Note that by increasing the number of turns the winding capacitance is increased resulting in a shift in the maximum impedance to lower frequencies proportionally.

This also suggests that getting a larger core is cost effective at the same time. Instead of getting 4 smaller cores, get a larger core and make a loop. You save 4 smaller cores. When 2 loops are made, that saves 8 smaller cores.

Number of loop(s)

Increasing suppression impedance

As if you are using as many as

1 loop (2 turns)



2 loops (3 turns)



3 loops (4 turns)



4 loops (5 turns)



Ferrite Cores don’t suppress desired signals in differential-mode. So, wind the cables as much as you can and add more ferrite cores as desired. Use cable ties or electrical vinyl tape to hold ferrite cores in place. Don’t let the ferrite core move on the cable. Please note that the ferrite core effectively suppresses noises emitted from cable however, it cannot block noises emitted from internal components directly. That being the case, proper shielding of the equipment may be necessary.

One other fact to note is that the longer the core is the higher is the impedance for a given volume of ferrite material. The split ferrite cores are about 6 times longer than those of donuts style ferrite beads or toroids and thus exhibit higher impedance.

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