There must be thousands of Youtube videos of “how to measure a common mode choke” to give a picture of some sort of the test configuration… though most lack important detail… and detail IS important in this case. Likewise there are lots of web pages on the same subject, and some have pics of the test configuration, again mostly lacking important detail.
For the most part, these show test configurations or ‘fixtures’ that might be appropriate for audio frequencies, but are unsuitable at radio frequencies, even at HF.
Connecting wires at radio frequencies are rarely ideal, the introduce some impedance transformation that may or may not be significant to the measurement project at hand. Such connections can be thought of as transmission lines, often mismatched so they have standing waves (meaning the impedance of the load appears to vary along the line.
Let’s take the DUT in my recent article Baluns: you can learn by doing! as an example for discussion.
Let’s take the saved s1p file from a S11 reflection impedance measurement as the example.
Above is a plot of the common mode impedance of the choke, solid line is |Z|, dashed line is R, dotted line is X. This was measured with connecting wires <10mm, see the original article. Continue reading Common mode choke measurement – length matters
Last update: 11th July, 2024, 7:03 PM
