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 you 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.

Ferrite 31500

Price: $4.45

Ferrite 311000

Price: $15.95

APPLICATIONS FOR THIS PRODUCT

Home Electronics

Computers

Ham Radio

TODAY’S USE

Many people in the electronics industry know the benefits of using ferrite cores in the ever-growing world of computerization and today’s home electronics environment. Computers and devices may emit noises that may cause malfunction. Manufacturers have taken certain measures to prevent that. As a matter of fact, many recent accessory cables of computers and devices are already supplied with ferrite cores. Just take a look at them. The cylindrical device often plastic molded in the size of a mushroom on the cable is a ferrite core. If yours don’t have them, you may have EMI/RFI in your computers, audio/video systems or other home/office electronics. But not to worry! You can immunize your entire house and office with our ferrite cores!

COMMON-MODE FILTERING (CMF)

Interfering signals can flow in cables in two ways: Differential-mode currents and common-mode currents. Differential-mode is the mode used by the desired signal on a transmission line. The cure for the differential-mode interference is a filter that passes the desired signal but blocks the unwanted signal. Examples are low-pass filters, high-pass filters and band-pass filters. Common-mode currents on a transmission line cause feed-line radiation. The cure for unwanted common-mode signals must somehow present high impedance in the common-mode without obstructing differential-mode signals. This can be done by use of a ferrite core. All conductors must pass through the same ferrite core, not a core for each conductor.

NEW FERRITE MATERIAL FOR CMF

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.

31 Material Magnetic Properties
Initial Permeability m Flux Density B (gauss) Flux Density B (mT) Residual Flux Density Br (gauss) Residual Flux Density Br (mT)
1500 3400 340 2500 250
 
Coercive Force Hc (oersted) Coercive Force Hc (A/m) Loss Factor @ frequency tan d/m (10-6 MHz) Curie Temp. Tc (C) Resistivity r (Wcm)

0.35

28

20 0.1

>130

3x1000

 

Physical Dimensions: inches (millimeters)
Part# Fitting Cable "B" Diameter (max)

Outer Diameter "A"

Length "C"

Impedance w/no loop(ohms)

31500

.5145 (13.05)

1.220 (31.0)

1.55 (39.4)

300 max
311000 1.020 (25.9) 2.220 (56.4) 1.69 (42.95)

375 max

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

INCREASING SUPPRESSION STRENGTH

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

Cost Saving Factor

1 loop (2 turns)

X4

 400%

2 loops (3 turns)

X8

 800%

3 loops (4 turns)

X16

 1600%

4 loops (5 turns)

X32

 3200%

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, however, that is beyond our intention.

One other fact to mention 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.
 

Back to the top