Intercepting Radio Signals

DISCLAIMER

This blog is written only for educational purposes. I will not accept responsibility for any illegal activity. Most countries require an amateur radio license to do such things.

In our modern world, understanding technology is highly crucial. Most of the devices we use in our daily life work with signals. In this blog, we will investigate radio signals.

Tracking Planes Using Radio Signals:

As we can see from the picture above planes have three types of communication which are, air-to-air communication, air-to-ground communication, and air-to-satellite communication. We will look into the first two of them (ADS-B). Commercial planes have to transmit ADS-B signals when they are flying, however, some pilots do not close their transponders even they are grounded. To decode these signals we are going to need an electronic device called SDR (Software Defined Radio) and software called dump1090.

You can find the Open Source software at https://github.com/flightaware/dump1090 and after you complete the installation we can use the SDRs.

These are different types of SDRs with different specifics and prices. My favorite is the HackRF One since it has a wide frequency range (1MHz - 6GHz, Rx-Tx, only about 100-150$).

However, you can get an SDR of about 10 bucks which will work fine for our project.

After installation, go to the directory where you've installed the dump1090 and run the following command.

./dump1090 --interactive

If there are planes in your detection area you will see a screen like this;

Extra Part:

If you own a Raspberry Pi, you can transmit ADS-B signals from its' 7th GPIO pin. However, this activity is extremely illegal and you will end up in prison

Visualizing Radio Signals:

Since you all have your SDRs already, let's get some wave visuals that look really cool. To do that, we are going to need software called cubicSDR. You can install it by using;

sudo apt-get install cubicsdr

After installation, we can run the software by typing

CubicSDR

on the terminal. After terminating the command we will see the starting screen that asks for the device to use.

In my case, I will choose my HackRF One and click start. After then, a waterfall diagram will show up where you can see signals.

When you are surfing on the spectrum you can find extremely intriguing communications such as taxi drivers' communication channels.

Receiving Real-Time Images from Satellites

I have not tried this in person but the idea and technique are very impressive. You can get real-time images from the NOAA (National Oceanic and Atmospheric Administration) satellites. Three of their satellites the orbit right now. These satellites are NOAA15, NOAA18, and NOAA19. They are orbiting around 850 Km far from the surface and transmitting pictures from two different frequencies. 137.1 MHz is for APT (Automatic Picture Transmission) and 1698MHz is for HRPT (High-Resolution Picture Transmission).

To find those satellites we will use software called Gpredict. You can run the following command to install the software.

sudo apt-get install gpredict

Then you can run by typing;

gpredict

This is the interface that we will see when we run the software. We can see satellites and more information about them. Moreover, this software tells us when satellites pass above us and where is the area that we can collect meaningful data.

NOTE: To catch signals we are absolutely going to need antennas. To calculate the length of a dipole antenna, it is half of the wavelength. To calculate the wavelength you can use the following formula;

λ = v/f

λ: wavelength

v: speed of the wave (equals to c (speed of light)

f: frequency of the wave

To catch APT signals we need approximately 54.3cm element length, polarize the antenna North-South direction, and the angle between elements should be 120°.

During the pass, you should record the signal using CubicSDR software. After recording, we need to decode the signal to get a visual. To decode the signal we will use software called noaa-apt which you can find on GitHub: https://github.com/martinber/noaa-apt/releases

After downloading the file you can install it by using the following command

sudo dpkg -i noaa-apt_1.4.0-1_amd64.deb

and run with

noaa-apt

A simple yet efficient UI will open

From the input file section, we can select the signal we recorded and start the decoding. Some people get extremely good results due to their line of sight, high-quality antennae, amplifiers, and filters. The perfect result looks something like this;

Thank You For Reading :)