CMC Choke Ferrite Slug Form

Overview

To get the maximum effectiveness out of any inductor, it is crucial to maintain consistent spacing between the conductors and prevent the windings from crossing over one another on the same layer, which can cause cancellations.

If you have ever tried to hand-wrap a common-mode choke (also known as a line isolator), you know how challenging it is to keep the coax perfectly tight and flush against the inner walls of the ferrite. That's why I designed this simple 3D-printed winding slug, and I'm hoping that others may benefit from it too.

Technical Specifications

• Compatibility: This slug is designed to slide directly into the center of a ½" Inside Diameter ferrite bead.
• Material Choice: For HF operations, using a Mix 31 ferrite core provides the broadest, most effective coverage.
• Capacity: The slug features precise tracks for exactly 9 turns of RG-316 coaxial cable, which requires approximately 3 ⅓ ft of coax.
• Performance: This setup delivers excellent common-mode attenuation ranging from roughly -40 dB to -26 dB across the entire 3.5 MHz to 30 MHz spectrum (80 m to 10 m bands).

💰 You can build this highly effective line isolator for a tiny fraction of the cost of typical US$75+ factory-made chokes on the market.

Constructive feedback is always welcome as I love tweaking these RF designs. If this slug helps clean up your signal or makes wrapping your chokes a breeze, please leave a thumbs-up and drop a comment!