DIY Lightning Detection with SDR: (Updated!)
What follows is an informal experiment to detect lightning using a Software Defined Radio. I’m using an RTL-SDR version 3 dongle and GQRX in Linux, but any SDR and spectrum analyser software that can tune VLF should do it. Many dedicated lightning detectors work by listening to frequencies below the AM broadcast band and this part of the spectrum is relatively quiet, so I chose to monitor 0 to 600kHz. The antenna is a 1/2 wave trapped dipole for HF but any bit of wire at least a few meters long will work.
In the above image, the waterfall display is the part in blue. Time is represented vertically and the span is ~30 seconds from top to bottom. The vertical line seen around 550 kHz is an AM radio station. The three thin horizontal lines are lightning. Here we can observe the broadband nature of lightning, comparative strengths and interval between discharges. Event #1 occurred first and was a large bzot producing thunder. #2 was a few seconds later and apparently weaker or farther away. #3 was a bit stronger than #2.
In this image event #3 was a large burst not far from here.
Update: Shortly after midnight on August 14th 2017 there was a spectacular display of cloud to cloud lightning almost directly overhead. Not wanting to miss the opportunity, I fired up CubicSDR spectrum analyser and watched the mayhem unfold. On this run, I max’d the sample rate to 3.2MHz and tried several waterfall speeds so I could view the pulses closer in the time domain.
Weather reports, satellite and radar images found online are not always accurate or on time. If you’re outdoors, boating or have antennas on the roof like I do, it can be helpful to know if an approaching storm brings lightning. I found that by tuning to a quiet part of the spectrum and setting squelch, lightning discharges produce an audible crackle, hence an audible alert without needing to listen to constant static.
There’s an interesting world-wide real-time lightning maps at:
- Kenn Ranous