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I built this fixture some time ago. It makes measuring chokes, baluns and ununs common mode very simple. The SOL(T) CAL loads are built onto the PCB.
My interest in common mode reduction now lies in VHF and UHF where this jig will not function because of lead lengths. All mounting hardware (except the banana sockets) has been replaced with stainless steel.

$50 includes USPS shipping in the USA.

Regards,
Dale W4OP

On Wed, Jan 29, 2025 at 08:36 AM, Dale Parfitt wrote:

W4OP

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John K0JHL

Interesting test fixture. Didn't know it existed.

I did it a different way..... and used a clamp on RF ammeter around the coax to measure CM current. Of course the CM current being measured will change, depending on where on the coax, it is clamped.
Still, the measurements can be taken in several different places on the coax. ( marked with painters green tape)....using CM choke #1. Then repeat, using CM choke #2. This also assumes the same power from the XCVR of linear amplifier is being applied. You will know asap, on the freqs being measured, whether CM choke #1 is better / worse then CM choke #2...( or CM choke #3/4/5 etc.