NanoVNA cable measurements

Having a VNA opens up so many possibilities for RF measurements. Typical measurements are antenna matching, RF filters, impedance matching and cable loss. But it an do more. You can use it even to measure the coaxial cable length – a task that is normally performed with time domain reflectometer (TRD), an instrument I have some knowledge about as I have designed/built few such circuits (Time Domain Reflectometer pulse generator, TDR kit, Avalanche pulse generator and Potato chip to TDR circuit).

Accurately measuring cable length with NanoVNA article will go through some mathematics on deriving TDR response with VNA data. Remember that the VNA does its measurements in the frequency domain. If we transform the frequency domain data into the time domain, we should see the time domain nature of our measurement (with certain limitations though). By using the magnitude and phase of the signal measured throughout the frequency sweep, we can compute the distance from where reflection occurred.

NanoVNA To Test The Loss & Length Of Coax Cables by Jim W6LG YouTube Elmer for Ham Radio Basics

The NanoVNA does many things. Two of which are testing coax cables for loss and length. Jim W6LG shows how to do both in this first video about the NanoVNA. In a subsequent video, Jim will show how the NanoVNA can be used to check antennas for resonance, impedance and reactance. The software that Jim uses is NanoVNA Saver. That software is free and easy to use.
Here is the link to the software :

#316: Use NanoVNA to measure coax length – BONUS Transmission Lines and Smith Charts, SWR and more

nanoVNA – Coaxial Cable Measurement Methods (Characteristic Impedance and Cable Loss) – VE6WGM

1. Calibrating the nanoVNA
2. The Smith Chart – Briefly (Begins at 8:24)
3. Measuring the characteristic impedance of coax cable. (Begins at 11:46)
4. Measuring coax cable loss. (Begins at 22:34) *Correction: At 23:34 I stated that the nanoVNA has a directional coupler. I have since discovered that this is not accurate information. The nanoVNA actually uses a bridge to make it’s measurements. My apologies. For more information on how this works, please see this excellent video here:

#502 NANOVNA Demystified

#37: Use a scope to measure the length and impedance of coax

Cable Basics; Transmission, Reflection, Impedance Matching, TDR

Reflected waves on a cable


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