Icom 746/756/765/775/781 RFI kit is designed to be installed on your radio transceiver to reduce Radio Frequency Interference (RFI) caused by common mode current on the coax output of your radio, the AC/DC power, USB, ALC/Send, mouse,mic and additional interconnect cables. Standard 756PRO Kit has 4 ferrite ring filters and 10 ferrite snap on filters and instruction manual or you can choose the optional CMNF-500-50 coax noise filter option for one or two antenna ports.
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, Mix 31, that is effective in suppressing radio frequency interference from transmitters and high noise floor on receivers.
The split beads 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.
Use of the chokes often helps cure SWR problems between transceiver and a linear amp and between transceiver and antenna tuner or direct to antenna. The DC power line choke helps keep common mode current out of the power line which could cause interference to other devices connected to the same power line if not suppressed.
Purpose. This kit is designed to choke common mode currents going into or exiting from your transceiver. Use of the chokes often helps cure SWR problems between transceiver and a linear amp (if used) and your antenna.The AC/DC power line choke helps keep common mode current out of the power line (or into your radio) which could cause interference to other devices connected to the same power line if not suppressed.
The Deluxe RFI Filter Kit includes the CMNF-500-50 coax common mode noise filter option which is highly effective in suppressing common mode noise carried in (or out) on the coax shield braid external surface.The ring filters used on the coax connector, the I/O cable filters and the DC power supply filter are effective from 1 to 300 MHz.
|
RFI Kit Part # |
CMNF-500-50 Coax Noise Filter |
F240-31 Ring |
FSB31-1/2 Snap On |
|
RFI-ICOM-756PRO |
None |
4 |
10 |
|
RFI-ICOM-756DLX |
1(*) + DMBC |
3 |
10 |
|
RFI-ICOM-756DLX2 |
2 (*) + Coax jumper |
2 |
10 |
*CMNF Connector Note:
First CMNF-500-50 comes with Double Male Barrel Connector (DMBC) for connection to chassis of radio.
Second CMNF-500-50 comes with 6 in RG-400 coax jumper for connection to radio since the spacing of the antenna jacks is too close for both noise filters to be connected.
Typical Installation Guidelines
RF I/O:Standard Kit: Ring filter – 8-10 turns of ¼”coax cable thru center
Deluxe Kit: Use CMNF-500-50 Coax noise filter with double male barrel connector or short coax jumper cable
AC/DC Input: Ring filter – 3-7 turns of AC/DC power cable
Send/ALC Amp Cable:Snap On – multiple turns through choke – ½” diameter hole
Band Control: Snap on – multiple turns through choke – ½” diameter hole
Audio I/O: Snap on – multiple turns through choke – ½” diameter hole
Digital Interfaces: Snap on – multiple turns through choke – ½” diameter hole
Note: if you have more I/O cables then ferrite filters, you can put more than one signal type wire through the same ferrite snap on.The ferrites filter the RFI/noise current common to all wires, but do not affect the differential signals internal to the wires.
Also make sure you connect a good RF ground to the transceiver ground post.Use multiple turns wherever possible to increase RFI suppression effectiveness.
If you use a linear amplifier use an amplifier RFI kit for additional RFI interference suppression.
Note: Icom 756PRO picture shown which is typical of filters and connection cables for all Icom and many other brand radios with similar I/O ports.
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.