Measuring coax impedance

I’m trying to determine a SMA to IPEX adapter impedance using a LCR meter following SQRT(L/C) . I’m a hobbiest, and do not have access to expensive impedance measuring equipment. I’ve had success with this on standard size coax cables but the not with the smaller IPEX to SMA cables, like in the picture below. I’ve tested 3 different cables which are supposed to be 50ohm but I’m receiving values in the range of 140-170 ohms. I’m following the procedure laid out here . Am I doing something wrong? Assuming the impedance is in the range of 150ohms, can I assume that signal loss is negligable since these connectors are extremely short?


The odds are in one’s favor betting on that theory. The referenced procedure indicates shorting one cable end; how is that being achieved? It’s possible that whatever mechanism is being used is contributing to the measurement.

Not necessarily; what’s “short” relative to another cable can still be “long” relative to a radio wavelength.

But if the measurements are off and the characteristic impedance of those adapters is more or less as advertised, problems stemming from that may be more imaginary than real.

The nature of hobby work is trial and error, often with a seasoning of misplaced attentions. Give what you’ve got a try; if it doesn’t work out and other theories are disproven, perhaps then it’d be reasonable to investigate the characteristic impedance of such a cable.

I’d compare the matter to building with a Lego set; if the result doesn’t quite resemble what’s on the box, measuring the bricks with a ruler probably isn’t the best way to understand why.

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