When considering solutions for FM broadcast (88 MHz – 108 MHz) you should consider Mix 31 or Mix 61 ferrites available in a variety of shapes and sizes. Choose a size to give the maximum number of turns of the affected wire or cable.
FM broadcast transmits on a high frequency with small antennas. Consequently it only takes a small ( less than 5 feet) antenna to receive the signals. Typical “antennas” are AC house wiring, phone lines, long satellite or cable TV cables, DSL/CAT5 lines running between rooms, speaker wires, electronic interconnect wires, etc. The device wires that connect to these “antennas” need to be choked with as many turns through the ferrite as possible. Some installation examples are shown below on this page.
For AC/ DC power cords and coax cables the F240-31 (2.4″ OD, 1.4″ ID) “Donut” toroid is the most popular. Also available are smaller toroid donuts and Mix 31 beads and Snap On split beads . Mix 31 ring toroid products are HERE and Mix 61 Snap On beads are HERE and Mix 61 small beads (for small wires) are HERE.
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Generic FM Broadcast RFI Kit
This RFI kit is designed to suppress RFI caused by FM broadcast transmitters in the range of 88-108 MHz and is useful for RFI signals from 20- 250 Mhz. The kit contains large ferrite toroids for the AC/DC power lines and snap on beads for input cables (like mic and mixer input cables) of RFI effected devices. The beads are easy to use, don’t require modification of the protected equipment and work in almost all cases, even when plug-in filters fail. Toroids have 1.4″ hole and SNAP ONs have 1/2″ hole – mix selected for the frequencies of interference.
Part # RFI-FM Price $125.00
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FM Broadcast interference to ethernet/CAT5/CAT6 cables
Ethernet cables in close proximity to FM broadcast antennas (on the same transmitting tower for example) can have FM RFI common mode current induced on the cable pairs from direct radiation, shared ground loop conduction or inductive or capacitive coupling between adjacent cables. In this case simple snap on ferrite beads can help to suppress the FM RFI. Depending on the severity of the RFI signal strength, multiple beads spaced 1/4 wavelength (at the interfering frequency – 1/4 wavelength (feet)= 234/f(MHz) apart along the ethernet line can provide additional suppression. Use at least 1 ferrite bead (FSB61-1/2) on each line and wrap 2 turns only through each bead. Each ethernet cable in a “bundle” of cables needs to have at least 1 snap on suppressor of only 2 turn each. Information and pricing on the FSB61-1/2 is HERE.
Typical Installations for Donut Toroids
 AC Cable on F-240 Toroid – 6 turns |
 Ethernet Cable on F-240 Toroid – 7 turns |
 Audio or Mic cable on F240- 12 turns |