FM Broadcast RFI Kit - AC/DC/Audio/Control, RFI Range: 1-300 MHz, 13 filters
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.
AM broadcast transmits on a low frequency with large antennas. Consequently it takes a large 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, 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 F240-77 (2.4″ OD, 1.4″ ID) “Donut” toroid is the most popular. Also available are smaller toroid donuts and Mix 77 beads. Shown below is a graph with 8, 10, and 12 turns through the toroid – obviously more turns has higher choking impedance. Mix 77 toroid products are HERE and Mix 77 small beads (for small wires) are HERE
Shown below is a graph of frequency response verses choking magnitude for a F240-77 in the AM Broadcast band for a 12 turn coil around the toroid. (Same info as above but different frequency range).
Typical Installations for Donut/Ring Toroids
Extra Mix 75 Snap On Beads HERE – VERY effective for AM Broadcast RFI