Beverage Antenna Coax Noise Filter, 1-60 MHz, Suppresses Common Mode RFI, 75 Ohm In/Out
Beverage Antenna Coax Noise Filter for AM Broadcast & HF from 1-60 MHz – F connector, 75 ohm input/output, 500 watts PEP
Purpose. The CMNF-500-75F is used to suppress RFI noise and common mode interference on the
coaxial feed line of beverage, EWE, and other receiving/transmitting antennas using RG-8 or similar 75 ohm coax feed lines.(also available for 50 ohm lines as CMNF-500-50)
The filter is designed to have a high RF impedance to noise and interference from common mode currents on the outside of the coax braid while passing RF signal currents on the center conductor and inside of the coax braid to the antenna.
The effectiveness of the filter is dependent upon the amount of common mode noise encountered on the feed line. If your receive system has a large amount of common mode noise current then you should experience a reduction of common mode current which usually as heard as background noise level. Typical choking impedance is shown in the gallery picture.
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