Using the wide band characteristics of SDR radios, it is possible replicate some of the functionality of much more expensive equipment such as a vector network analyzer. Actually what SDR can do it scalar network analyzer functionality. A scalar network analyzer can measure amplitude, but a vector network analyzer can measure amplitude and phase and is a more complex device. I have already measured RF filters with my RF noise source and RTL-SDR. Next step is antenna measurements.
SWR stands for “standing wave ratio” and is a measure that can be used to tune an antenna for a particular frequency. The closer the SWR is to 1:1 at the designed antenna frequency, the better the antenna will receive (and transmit).
RTL-SDR Tutorial: Measuring filter characteristics and antenna VSWR with an RTL-SDR and noise source article tells that in addition to SDR and noise source for determining VSWR you will also need a directional coupler. To measure the VSWR of an antenna we will use the directional coupler in reverse: connect the noise source to the output of the coupler, the antenna to the input of the coupler and the RTL-SDR dongle to the coupling (CPL) port of the coupler.
Here are some instructional videos how to make measurements:
This is the end of this post. I am still in the process of trying to find the optimum way to measure the antennas with RTL-SDR.
At the moment I don’t have a good 50 ohms directional coupler for doing the measurements. I am experimenting with some ideas with the hardware I already have to see if I could live without investing to a possibly expensive and hard to get directional coupler. I plan to write results of those experiments later when I get more results.
Documents that tell how to do antenna measurements: