Use for 3/8″ Cable – RG-8X, LMR-240, etc
For 3/8” cables use five FSB31-3/8 split beads for 80-10 meters (3-30 mHz) or ten FSB-3/8 split beads for 160-10 (1.8-30 MHz) meters or use 15 FSB31-3/8 for even higher choking for 1-10 MHz.
Typical Impedance per split bead: 10 MHz: 100 ohms, 25 MHz: 163 ohms, 100 MHz: 275 ohms, 250 MHz: 275 ohm
Minimum recommended total impedance is 500 ohms at frequency of interest.
The beads clamp to the cable and may be operated as is for indoor use. However, it is strongly suggested that they be covered to protect the plastic covers from weathering – use electrical tape for best results or heat shrink to ensure longer life. All kits come with instruction manual which covers assembly and application tips.
As you can see from the impedance vs frequency graph, you can very effectively increase the choking impedance by increasing the number of beads on the cable.
12:1 Ununs are useful between coax and long wires with a load impedance near 600 ohms like a beverage antenna. Shortwave listener antennas also can benefit with the 12:1 unun and it may provide a better match than 9:1 ununs – this means quieter noise levels and stronger signals so you can hear distance stations easier.