RF Choke

Overview

An RF choke presents a high impedance to radio-frequency current while passing direct current and audio. In a station it is used to stop RF travelling along cables where it does not belong — power leads, microphone leads, USB cables, and the shield of the feedline.

The classic construction is a ferrite core with several turns of the offending cable wound through it. The impedance rises with frequency and with the number of turns, which is why a stack of clamped cores on a power lead often clears up an interference problem that no amount of re-routing could fix.

Bands and modes

Band coverage

Modes

Safety note

Using it well

• Fit chokes to the cables leaving the radio, not to the radio itself.
• Use clamp-on cores for anything you cannot cut, especially mains leads.
• Add turns through the core until the interference stops or the core is full.
• Fix the antenna-side problem first; shack chokes treat the symptom.