Common Mode Current Choke Test Rig

This product is a kit that requires assembly by the user.  Assembly instructions are here. There’s also a User Guide, documenting how to use the CMCC Test Rig.

This YouTube video, originally presented at the QSO Today Ham Expo, Fall of 2021, shows how to measure common mode current chokes using a NanoVNA.

In that video, Smitty describes two versions of a test rig he built to perform those measurements.  This is v3.1a of that test rig.

tl,dr: Vector Network Analyzers (VNA) such as the NanoVNA, measure differential power, which travels on the inside of a coaxial cable.  Common mode current, which travels on the outside of coax, is not normally seen or measured by a VNA.   If we wish to measure the effectiveness of a common mode current choke (aka “Current Balun” or “1:1 Balun”), we have to get the signal from the VNA onto the outside shield of the coax.  This test rig does just that: It routes the center conductor from the VNA to the shield of the device under test.  Connect a common mode current choke (or any device you wish to measure the common mode properties of) to any of the available sockets: SO-239, N, BNC, or SMA, and measure the “S21 LOGMAG” on your VNA to directly measure the effectiveness.

For a common mode current choke, you want as much loss in S21 LOGMAG as possible, across as much of the intended frequency range as possible (eg: the HF spectrum.)  Ideally, it would be at least 25db of loss (an S21 LOGMAG of -25db) from 3MHz to 30MHz.  More loss is better.