Ham Tech Page
If you own an antenna fed with coax, you need RF chokes on the feedline! Using a balun with adequate RF choking impedance will improve the performance of your antenna, prevent pattern distortion, and prevent RF coming down the feedline, which can cause RFI. Many balun manufacturers either don’t make baluns with enough choking impedance, or are overcharging for a product that can easily be made by the ham (and much more effective!).
Ferrite is a ceramic consisting of iron and metal oxides having high permeability. When a conductor is passed through the center of a ferrite bead, the impedance goes up with the SQUARE of the number of passes through the center. To achieve the same amount of choking impedance of a toroid with a few turns through the center, a “string of beads” choke can require 30, 40, 50 or more beads! Ferrite is made in different formulas, called mixes. The mix used will determine the best choking impedance for the desired frequency range. Mixes 31 and 43 are best for HF use (31 is better for the low bands, with mix 43 having a slight advantage from 14 to 30 MHz). I currently stock mix 31 and 43 ferrite. Let me know if you are looking for something in particular. Chris at KF7P dot com.
Check out our TECH page for lots of information on ferrite material and how to properly use it.
Ferrite Products for RF Chokes, Baluns, and RFI Mitigation