# Measuring the impedance of a transmission line

I designed a Tem Cell and I need to measure its impedance which I have no idea how I can do that. I have tracking generator, signal generator and 50 ohm terminations. So how can I measure the impedance of this transmission line? P.S: Can you explain it like explaining it to a beginner ( I am one). Another P.S: I am not a native speaker so feel free to edit the question.

• You can't measure anything with that list of equipment. Commented Jan 3, 2020 at 10:05
• I also have a multimeter and a digital oscilloscope. Commented Jan 3, 2020 at 10:32
• I'd use the signal generator to produce a thin repetitive pulse and look for the reflection coming back on the o-scope. No reflection means perfect impedance match. Adjust the generator driving impedance (nominally 50 ohms) using series parallel resistors to obtain no reflection. Commented Jan 3, 2020 at 10:41
• Thank you. So why there won't be any response in case of perfect impedance match? Commented Jan 3, 2020 at 10:46
• Because the voltage and current waves travelling down the coax (assumed to be 50 ohm) will meet the correct impedance (50 ohm) at the TEM cell and there will be no reflected power under these conditions. Commented Jan 3, 2020 at 10:51

## 1 Answer

I would use a time domain reflectometer(TDR) to measure the impedance of your transmission line. It will tell you the impedance of your transmission line as well as where your transmission has changes in impedance. TDR's works by applying short square waves with a set rise time and then will measure the reflections in your transmission line. Then the TDR will use these reflections to calculate the impedance and position of the impedance changes.