Palomar Engineers RFI Filter Kit for CB Radio Radio Transceivers from 20-30 MHz uses ferrite rings for the DC power supply and the coax to the antenna.
BUY THIS KIT NOW TO SOLVE YOUR RFI/EMI NEEDS! WORKS WITH ALL BRANDS (Cobra, DAS, Midland, Uniden etc.) OF CB/HAM/COMMERCIAL RADIO RIGS in 20-60 MHz range.
Purpose
The RFI kit is designed to be installed on your radio transceiver to reduce Radio Frequency Interference (RFI) caused by common mode current on the outside of the coax braid at the output of your radio and on the DC power supply cable.
This kit will help reduce or eliminate:
1. “Hot mic” RFI caused by poor grounding of antennas or common mode currents from linear amps feeding unbalanced (coax fed) antennas without baluns/line isolators.
2. RFI to neighbor’s electronic devices including audio/video systems, computers, telephones, garage door openers, etc.
3. RFI to your other radios, audio/video systems, computers, telephones, etc.
A side benefit is a reduction in noise floor in your receiver depending on the amount of noise being introduced by common mode currents (which are blocked/reduced by the chokes in this kit).
These chokes use a special mix of ferrite core material that is effective in suppressing radio frequency interference from Ham Radio amplifiers.
Included are the following chokes and installation guidelines:
DC Input: F240 Ring – 3-7 turns of DC power cable - sized for smaller plugs
RF Input/Output: F240-31 ring - wrap 6 turns of RG8X size cable near the back of the radio
For additional RFI suppression, use a MC-1-500-50 mini feed line choke at the antenna feed point to suppress common current on the coax feed line during transmit and a CMNF-500-50 Coax Noise Filter to reduce common mode noise during receive operations.
If you use a switching power supply for base operation, consider the RFI-SMPS switching power supply RFI kit.
If you use a linear amplifier we have RFI kits for linear amplifiers that help suppress RFI in your shack or in your neighbor’s house.
Often it is difficult to slip beads on a cable because of a plug or connector. Split beads solve this problem. They come in two halves that fit over the cable. A plastic snap cover holds the two halves together and holds the assembly on the cable.
For RFI use, mix 31 is effective from 1-300 Mhz, mix 43 works from 20-250 Mhz, Mix 61 is for 200-2000 Mhz, and mix 77 favors .1-20 MHz. These frequencies are those of the interfering signal to be eliminated, not the operating frequencies of the equipment to be protected.
Not sure of what sizes you need or solving a RFI problem with devices using multiple size cables? Try the Ferrite Snap On Combo Pack which has sizes from 1/4″ to 3/4″ with either Mix 31 (1-300 MHz) or Mix 61 (200-2000 MHz) or Mix 75 (150 KHz – 10 MHz).
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Bead dimensions are shown in the picture below and in the table as A, B, C
Ferrite Split Bead Dimensions
Application Notes
Application Note for using these Snap On split beads: How Many Chokes do I need?
You can very effectively increase the choking impedance of smaller cable by using a large hole ferrite bead and wrapping the cable through several times. For particularly difficult common mode current/RFI problems you may need a choking impedance as high as 5-10K ohms. Using multiple beads and multiple turns through each bead will give higher impedances up to a point. At higher frequencies, when the number of turns approaches an electrical wavelength, the choke becomes resonant due to stray capacitance and the inductance of the cable and limits the high end impedance values to less than the above table points.
Some example of ways to wrap cable are shown below.
 FSB-1/4 – 1 turn |
 FSB-1/2 1 turn |
 FSB-1/2 Open Shell |
 FSB-1/2 2 turns |
 FSB-1/2 3 turns |
 FSB-1/2 4 turns |
—–//—–
More examples of split bead use
Ethernet Cable on FSB-1/4
Ethernet Cable on FSB-1/2 – 3 turns for 9X Impedance good filter for 15-30 mhz between 2K-3K ohms choking Z
Three Effective Radio Interference Filters
 FSB-1/4 or FSB-1/2 4 turns for 14-50 Mhz 2K-3K Z |
 FSB-1/2-5 turns for 10-30 Mhz 2K-4.5K choking Z |
 FT240-43 – 14 turns for 3-14 Mhz or use two FT240-43 for 1.8-10 Mhz |
These snap-on chokes are useful for reducing RFI in public address system amplifiers, speaker wires, mic cables, mixer panels, coax cable, telephone wires, computer sound card speakers, dsl/cable connections, remote control heads for ham transceivers (Especially FT-100, FT900, IC-706, IC-7000), AC power cables, DC power cables, home theater cables, video cables, HI Fi cables, guitar amps, linear amp cables, etc.
They are also helpful in suppressing common mode noise/RFI in radio and TV receivers, audio and RF amplifiers. They can also help suppress noise generated by treadmills, exercise equipment, fish tank heaters, oil heater pumps, fluorescent lights, motors, cable modems, DSL modems, computers, and many other electrical devices. Common mode current reduction in computer cables often helps speed up computers.