Airband Monitoring

Introduction

I got the idea for this project as recently 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 a 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 atleast thats how I've come to understand the meaning.

At this point I was still under the impression that this would be a quick sideproject where I could as per usual get a working prototype done in just a few days be happy that I've managed to do something and then just forget it and let it rot in my github for all eternity. As it will come very clear there was a bit more to it than just pluggin the radio in.

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First antenna

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 airtraffic 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 and from that calculate the dimensions for the antenna.

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 lenght $\approx2.19\,\text{m}$