Coax antenna switches generally only switch the center conductor of the coax and all the coax braids remain connected in parallel summing the common mode noise off ALL coax lines onto the coax selected - this means you may be picking up common mode noise from coax lines that are not even connected to the coax antenna selected. The only practical solution is to isolate the coax braids from each other BEFORE they connect to the antenna switch as shown in the picture for a FLEX RADIO Antenna Genius 8 port switch or just a simple 2 position antenna switch. This product listing is for antenna switches from 2 - 8 antennas. Each switched line needs a common mode noise filter prior to being connected to the switch. In some cases you can use a double male barrel connector to attach the filter to the switch or you may need a short jumper cable. We offer a low power filter (CMNF-500-50 up to 500 watts PEP and up to 46 dB of common mode noise suppression per line) or a high power (Maxi-Choker, MC-1-1500 up to 1.5KW PEP and up to 42 dB of common mode noise suppression per line) and 2-8 ports of antenna switch. If you use a dummy load for one of the switched ports you do not need a filter for that port. Each filter has a range of 1.8 to 61 MHz (see individual listing on this website for specifics). Picture shown is 8 port FLEX RADIO Antenna Genius at AK6R with one dummy load and 7 antennas. Inputs to Antenna Genius is from TUNER GENIUS with SO2R option. This kit also includes 1/2 snap on filters for the ethernet line and the 12 volt power supply and two 1" snap on filters for the RF input lines (1/2" ID RG-213 shown and also works with 1/4" ID RG8-X/RG400, etc.).
$19.95
For RFI common mode suppression use, mix 31 is effective from 1-300 Mhz, mix 43 works from 25-300 Mhz, Mix 61 is for 200-2000 Mhz, and mix 77 favors .1-50 MHz. These frequencies are those of the interfering signal to be eliminated, not the operating frequencies of the equipment to be protected. See Mix Selection for other applications.
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Bead dimensions are shown in the picture below and in the table as A, B, C
Ferrite Bead Dimensions
Application Note: Use impedances for each bead at your desired frequency to select number of beads needed for desired Z. For example if you have a 50 ohm RG-8 coax cable and want a choking impedance of 500 ohms at 10 Mhz, you can check the FB102 column (since FB102 will pass RG-8 through its center ID) at 10Mhz and find that Mix 31 has a Z of 108 ohms/bead and Mix 43 has a Z of 91 ohms/bead. For 500 ohms we would need 5 mix 31 beads or 6 mix 43 beads to have greater than 500 ohms. Mix 31 has better response below 10 Mhz but above 10 Mhz mix 31 and mix 43 are very close. If you need more Z, just use more beads in series on the cable or use more windings thru a larger ID bead (e.g. USE FB102-31 for 4 turns of RG-8X for 16X increase in Z per bead – see pictures below for examples). Use Mix 61 for VHF and above for RFI/EMI suppression and below 30 Mhz for multi-ratio impedance transformers (baluns/ununs). See Mix Selection for other applications.
For extra large cables use the FB400-31 which has an inside diameter of 3 inches (76mm).
Frequency Range Comparison Chart
(FB56-xx size)
Multi-turn Common Mode Choking Impedance Increase Example (FB56-43)
Ferrite Bead relative size comparison
Left to right sizes: FB56 (ID = .25″), FB102 (ID=.505″), FB103 (ID=.77″)
SLIP ON Sizes for Heliax and Coax Cable
Cascaded Common Mode Chokes/Line Isolators/1:1 Baluns
 RG58 4 turns on 2 FB102-31 for 2000 ohms choking impedance |
 RG58 12 turns on FT240-43 for 4000-6000 ohms choking impedance |
Handy Wire Size reference for ferrite bead sizes needed
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Connector already on cable? See Snap On Ferrite Beads for convenient installation on cables with connector already installed.