Current Choke by Rig Cables

Rig Cables is proud to offer Current Choke assemblies for your station.  A current choke (also called a common-mode choke, feedline choke, line isolator, or sometimes a 1:1 current balun) on an antenna feed line in a ham radio setup primarily suppresses common-mode RF currents flowing on the outside of the coaxial cable shield.  We only use premium Times Microwave LMR-240 or LMR-400 Ultraflex coax, as well as Fair-Rite Mix 31 ferrites.

Ideally, a current choke should be installed at your antennas feed point and at your radio.  However, there are some exceptions, such as end-fed dipoles and G5RV's, to name a few.  In cases like these, the feedline is designed to radiate RF, so a choke at the antenna would reduce the antennas performance.

We offer Current Chokes as a stand-alone product, or you may add them to your longer coax builds.  We find that 5-ferrites is a sweet point, offering 20-35 dB of attenuation.   

Why It Matters

Without a choke:

• The coax shield can act as part of the antenna, radiating RF (or picking up noise) unintentionally.
• This leads to distorted radiation patterns, higher RF in the shack (possible "RF bite" or equipment issues), increased RFI/EMI to nearby devices, and more noise on receive.
• It can also cause unexpected SWR changes or inefficiency.

The choke creates high impedance to these unwanted outer-shield currents while leaving the desired differential-mode currents (inside the coax, between center conductor and inner shield) unaffected. It helps keep all the RF on the antenna itself and isolates the feedline from becoming an unintended radiator or noise collector.