Fish Finder – Sonar RFI Kit
Fish Finders/Sonar units can cause RFI “noise” in other electronic devices on a boat including audio and video systems, radar, SSB, wind/speed/depth instruments, etc. Likewise other electronic devices can also interfere with the fish finder and cause erroneous depth/temperature readings.
Palomar Engineers has developed a simple to install fish finder/sonar RFI suppression kit to solve the RFI noise problem aboard recreational and commercial boats.
Just slip a split bead on the transducer cable (1" ID) and use the 5 1/2" ID split beads on the fish finder/sonar readout unit transducer input and DC cables. Use the extra ferrites on other equipment needing protection like the Radar, radio, etc.
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
F240-77 Turns Comparison from .1 – 8.1 Mhz
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).
F240-77 Choking Impedance in AM Broadcast Band
Typical Installations for Donut/Ring 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 |
Extra Mix 75 Snap On Beads HERE – VERY effective for AM Broadcast RFI