Measuring the SWR of FPV Antennas with an RTL-SDR
FPV stands for 'First Person View', and is a term used to describe the hobby of flying remote controlled aircraft entirely via the view from a wireless camera that transmits live video to the pilots screen or video goggles.
Part of the FPV hobby is to not only enjoy flying, but also to tweak the wireless video equipment for maximum range and reliability. This involves measuring the SWR characteristics of FPV antennas. SWR is a metric that describes how well the impedance of an antenna is matched with the receiver at a certain frequency. Poor SWR results in additional signal loss on top of cable and connector loss. We note that SWR is only one antenna metric, and doesn't take into account radiation pattern and antenna gain which is often more important, but it is the easiest metric to measure and control, and should give you some idea as to if an antenna was designed and tuned properly.
As FPV hobbyists are often not hams or radio professionals, most don't have access to the equipment required to measure SWR. So over on his YouTube channel bonafidepirate shows how he's been using a cheap RTL-SDR, noise source and RF Bridge to measure the SWR of his FPV antennas. The process is similar to the one shown in our tutorial, but he uses the Spektrum software which allows you to measure SWR entirely within the software itself.
In the video bonafidepirate goes over the required hardware, software and the setup, and then demonstrates several SWR scans of different FPV antennas.
Mister BonaFidePirate- I have SDR# installed on a Windows 10 laptop hooked up to an Elonics E4000 Tuner (frequency range 55 – 2300 megahertz). I have this SDR# television plug-in installed: http://www.rtl-sdr.ru/page/obnovlen-tv-plagin Could my setup be used to share the view through drone cameras? If yes, would you favor us with a tutorial?
If you are in the USA, these transmitters are considered illegal. Hobby King was fined a huge sum for selling them. They use frequencies that are not authorized for that kind of use.
Some of the 5.8 mHz video transmitters are capable of using frequencies that are out of the ham band. If you are transmitting under an amateur radio license it is up to you to only use the legal frequencies in which case it is perfectly fine. It is not legal in the US to transmit without a license as nearly all of the VTX units are not FCC type accepted.