[TowerTalk] Feedline (choke) question

[Brian Beezley]

On 9/25/2025 8:27 PM, David Gilbert wrote:


"3.  A common mode choke, like any other inductor, isn't going to have 
much effect at a current minimum, so placing common mode chokes at 
current maximum(s) along the coax seems like it would be good additional 
protection ... and they aren't necessarily located at either end of the 
coax.  Note that this would be the current maximums for the common mode 
current, not necessarily for the differential current.  It would 
probably require a field probe to find those points if they exist."


Dave, I don't think it would be hard to locate suitable points with an 
impedance probe or RF ammeter. But adding a choke normally requires 
severing the coax and installing connectors. I wonder if anyone has 
looked into using several large split ferrite beads clamped over the 
coax for this application. Even if their impedance was less than that of 
of a good toroidal choke, they might solve the problem. I know that CM 
chokes used to be made this way, but I don't know their impedance 
properties.

Brian