Airband Monitoring

Introduction

I got the idea for this project recently as I've been interested in collecting and processing data. While working on my nginx logger I found myself bored and thinking of other kinds of more interesting data I could keep track of. I remembered that a while ago my father gave me a (fake) HackRF One SDR.

SDR or Software defined radio is just an implementation of a radio where components that are conventionally analog are implemented digitally. Or at least thats how I've come to understand the meaning.

First antennas

My first goal was trying to listen to airtraffic communications. I thought that this shouldn't be too difficult as even though I can't get the antenna in a particularly good spot, there is a lot of air traffic above my house to the Helsinki airport.

After a bit of searching I found that the VHF Airband is in the range 108-137Mhz. From this I could calculate the wavelength.

The basic wave equation:

Where $c$ is the speed of light and $f$ is the frequency

We can use a simpler formula for MHz to meters:

Now if we do the calculations for 137Mhz
We get the length $\approx2.19\,\text{m}$

Making an antenna this large would be difficult so we will divide this by four to get the quarter wave length $\approx54\, \text{cm}$

After this I made a few different 55cm dipole antennas from aluminum tape and also from stereo cable, but due to the antenna still being quite large I couldn't get it mounted well enough to hear any vocal communication.

I kept at it for a few days experimenting with the antenna placements when finally with an antenna taped to the outside of my window I heard some very faint ATC communication. This for a very brief moment felt like a victory but it quickly became a hollow one as that was really the only little success I had.

After all of this I couldn't just leave it at that as I never really felt that I'd succeeded in utilizing the receiver well. So I decided to shift the focus of the project to ADS-B communications.