Following is a list of large size Ferrite Beads (FB), Ferrite Toroidal Cores (FT), and Split Ferrite Cores (2X), all of which are extensively used for RFI problems involving multiple wire bundles, coaxial cables, microphone cables, AC cords and computer ribbon cables. These larger ferrite beads and toroidal cores can provide larger ID to accommodate the larger diameter coaxes and wire bundles.

The 43 material is a good all around material for most RFI problems. However, the lower frequencies from .5 to 10 MHz can best be served with the 'J' material. The 77 material can provide excellent attenuation of RFI caused by amateur radio frequencies from 2 to 30 MHz and the 43 material is best for everything above 30 MHz. However, it is still very effective across the entire amateur band but not quite as good as the 77 materials. The 73 material is specifically a ferrite bead material having a permeability of 2500 and can provide RF attenuation very similar to the 77 core material.

When more impedance is needed (with any bead or core) use additional cores on the same conductor or a core with a large enough ID to accommodate multiple wire turns. When additional cores are added, the impedance will be additive, but when additional wire turns are added the impedance increases to the number of turns squared.

Split beads and 'bars' are also available to that they may be installed without removing the end connector from the cable. Split bars are especially designed for computer ribbon cables. They are presently available for 1.3", 2.0" and 2.5" computer ribbon cables. Two or more may be used on the same cable to increase the impedance.

Shown below are typical impedances in ohms at 25 and 100 MHz with only one pass through the core.

(table/diagram)