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Common Mode Current Choke Test Rig

$59.00

Designed for measuring the effectiveness of common mode current chokes, this test rig diverts the signal being measured by a VNA (Nano- or otherwise) to the SHIELD of a coax cable. Works on cables with a variety of connectors: PL-259, N, BNC, or SMA. Non-coaxial cables (eg: power cords) can be measured using the banana plugs.

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.

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SKU: CMCC-v3.0 Category: Tag:

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 v3.0 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 “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” 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.

Weight .2 lbs
Dimensions 12 × 8 × 4 in
VNA Ports

SMA

Device Under Test Ports

SMA, BNC, SO-239, N, Banana

1 review for Common Mode Current Choke Test Rig

  1. Terry

    If I can build it (and be pleased with the result) then anyone can. Clear instructions, “good quality ingredients” just take it steadily, and all will look very professional on completion. The price is fair as well.

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