SDR

I recently came across the Software Defined Radio (SDR) community. It turns out that you can use a small USB dongle to capture and decode signals from a wide range of radio frequencies. Sure you can do boring things like listening to FM radio or tracking airplanes, but you can also capture cool images of the Earth from weather satellites! Korea happens to have a geostationary weather satellite GEO-KOMPSAT 2A (GK-2A) near me that actively sends data to the ground, so I decided to give it a try. The weather satellites usually work at very high frequencies with very weak signals, so it is a challenging task to capture them properly without specialized tools. This short post walks you through my setup and the process of capturing the images. Feel free to reach out to me for more technical details.

Here is the first setup that I tried, a simple dipole antenna on a tripod with an aluminum dish as a reflector. It quickly turned out that both of them were too weak to capture the weak signals from the satellite at the required frequency (~1.7 GHz).

To improve the reception, I built this Yagi-Uda antenna with dimensions specific to the frequency of the satellite signals. The signal strength was improved, but the antenna alone has a very narrow beamwidth and requires a wider reflector.

So, I built a bigger reflector out of an old umbrella and some aluminum foil. Although this is the design that finally seemed to work, I still had to spend some frustrating hours with no signs of life. The setup seems to be too sensitive to small changes in the antenna's alignment.

I am lucky to live in a place with the satellite almost over my head (48.7 degrees elevation), which makes this setup enough to capture the signals. The received images are in grayscale. After some post-processing, the final image looks like this:

The satellite sends the images about every 10 minutes. I am waiting for the weather in Korea to get colder a bit to leave my setup outside for a longer period of time and capture more images. Enough of them captured, I will try to make a timelapse video :) Feel free to reach out to me if you would like to know more about the setup or the process.