Getting Started with Wireless Communication – Setting up a Flight Tracking Receiver

We recently had a 16 year old student in our labs, and tried to teach him something about LTE, RF transmitters, spectrum analysis, and so on. Most of the stuff however was far too complex for him to understand, as many of the mathematical basics were missing. After talking to him for a day and doing weird measurements, it popped to my mind that I still have this DVB-T Stick and a Raspberry Pi at home, which might make a really cool project. So I brought both devices the next day and told the student to do some research on and find a project he would like to do.

He wanted to track airplanes, as he found a flight tracking webserver could be easily implemented with the RTL-SDR stick and the Pi. What’s this flight tracking, anyhow? Airplanes are sending broadcast messages with information on their flight code, location, altitude, direction, speed, and many other information. The system is called ADS-B, Automatic Dependent Surveillance Broadcast, and the messages are modulated on a 1090 MHz carrier signal and sent once or twice every second.


We just need the RTL-SDR Stick, an 1GHz vertically polarized antenna, and some receiver software. So we went to the lab and were soldering a simple dipole antenna with a length of roughly 7.5cm. Other antenna examples can be found on the project webpageof Then we downloaded dump1090-mutability software, the compilation was easy with standard tools.

Plugging everything together, holding the antenna out of the window starting the software, and immediately we received some messages! We were of course immediately googling at the coordinates, to see where the airplanes were located and were heading to.


It took us a 1 hour effort to build an antenna and compile the software, and could receive some digital radio messages from far away. Pretty cool, isn’t it?


On Teaching Wireless Communication – with a Raspberry Pi

Smartphones, PCs, Televisions, internet, cellular networks, Wifi, Bluetooth; we have seen dramatic increase in complexity of devices, servies, and technologies while theay are easier and easier to use. A huge step forward to enable use of technology not only to nerds and geeks, this trend also results in the fact that nearly nobody understands and nobody can explain his kids how these devices and systems work. Teaching and explaining wireless communication gets more and more complicated, as we lack simple examples and devices. Some decades ago, it was easily possible to disassemble and debug your TV, Radio, or other electrical equipment, make some experiments or try to fix it.

The current PISA report in Germany revealed, that students are good in Math and Science, but are heavily lacking interest in these fields. One of the projects targeted at fueling interest in programming and computers is the Raspberry Pi as simple learning platform for anything related to computing. The success is amazing, now having sold 10 million devices of the Raspberry Pi and fueling huge interest in the making and creating things.

There are plenty of cool and fun projects on the webpages like With these ideas, plans, and descriptions, a rewarding project can be very easily built. Questions on the basic principles of the project can follow, which can be answered by a friend, relative, or teacher. On the second hand, it’s very easy to experiment and to explore. The combination of getting started easily, rewarding projects and room for experimentation makes the major success of the Pi.

In the next couple of posts I will write how to use the Raspberry Pi together with cheap Hardware and open source software to conduct projects and experiments to learn something about wireless communication.

Polar Modulation explained

“What do you actually do at work?” – ” Uh, well, this is hard to explain.  Today, I was doing optimization of DPD coefficients for 3G higher order modulation cases”. When people asking us highly specialzed engineers, scientists, or researchers about their work,  we are sometimes stuck and can’t explain what we are actually doing, but rather explaining very basic, undergraduate course topics, which leaves both us and them puzzled.

With this blog post I want to start a new series on my actual work, with a more educational vision: The desire to explain basic principles of my work to people with no background in electrical engineering, but with following articles including deeper explanation of advanced techniques. The first example seems to be randomly chosen, but this technique is actually used in data connections of the modern mobile phones (smartphones), so it’s definitely worth  explaining; I am talking about Polar Modulation.

So, what is Modulation?

The goal of wireless communication is transmission and reception of information  with the help of electromagnetic waves over the air, without wires. For example in audio broadcasting, the electrical signal representing the sound is transmitted over the air and can be receipt at a distant place with a radio receiver. As several stations want to be heard, the radio spectrum is organized in channels, and each station is only allowed to send a signal in it’s own channel. A channel is a range of frequencies, and Modulation is the term for the mechanism of bringing the desired information into frequencies of the desired channel. It includes a frequency translation, in the example of a radio the audio signal spans frequencies up to 20 kHz,  but the carrier frequency is around 100 MHz (in FM radio). The eletrical device which forms the carrier signal out of the underlying signal is called a Modulator.

Modulation as frequency conversion to a channel frequency of 100MHz

What does Modulation actually do?

Let’s explain with a simple example: music. While the term modulation means something different in the context of music, we can use music to explain polar modulation. The art of music lies in the artful combination of notes with different volume. A piano player can play louder high notes and lower bass notes; but he can also play louder bass notes and lower high notes, both volume and key are completely inedependent. As you probably know from the physics course, each note has a different base frequency.  The piano player is therefore altering both the amplitude and the frequency of the generated sound completely independently.

In wireless communication, equally to the example of a piano, the concept of altering the frequency (phase) and the amplitude of a signal indenpendently also exists. If the signal is thought of as a vector, it can be represented with  both phase and magnitude, meaning in polar coordinates. Therefore we are talking about polar modulation. Let’s have a closer look at the modulation itself. The transmission signal T(t) can be described by a cosine-wave:

T(t) = A(t) cos(ωt+φ(t)),

where A(t) is the modulated amplitude, φ(t) is the modulated phase, and w is the carrier frequency. But wait, we were talking here about frequency, not phase, so how are they related?  The phase of a sinewave is changing over one period from 0 to 2*pi, the shorter the period thefaster it changes; and the higher the frequency.  As we are talking on change versus time, the frequency is therefore derivative of the phase with respect to time, ω = dφ(t)/dt.


If we now find a device which can generate a signal with tunable frequency and tunable amplitude, we can build a Polar Modulator. Such a Transmitter has been built a Raspberry Pi, I will talk about that in my next posts. If the Pi is up and running, I will show measurements, and describe both the general and uniqe properties of the polar modulator based on a Raspberry Pi.

Source Code of Bibtex Graph Generator





A Graph Display Software for bibtex databases
 Copyright (C) 2015 Benjamin Laemmle, jdmorise a t
 (at your option) any later version.
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 GNU General Public License for more details.
 You should have received a copy of the GNU General Public License 
along with this program. If not, see <>. 

usage: "Examples:

optional arguments:
 -h, --help show this help message and exit
-if INPUT_FILENAME, --input_filename INPUT_FILENAME 
          Filename of publication database in bibtex format
-gf GRAPH_FILENAME, --graph_filename GRAPH_FILENAME    
          Filename of graph output stored as png
-ma MAIN_AUTHOR_NAME, --main_author_name MAIN_AUTHOR_NAME
          Only add edges with ERT or more number of relations
          Only add authors with ART or more number of relations
          Only add authors with APT number of publications
-lvl LEVEL, --level LEVEL
-b BEFORE, --before BEFORE     
          Only use Publications before YEAR for the graph
-a AFTER, --after AFTER
          Only use Publications after YEAR for the graph
          Graph Programm for rendering the graph. one of the
          following: fdp,dot,sfdp,circo,twopi.




python -if Darabi.bib -gf graph_plain.png



python -if Darabi.bib -gf graph_red.png 





Male and Female Coauthors of #TimHunt









Studying Research Dynamics of an Author with Timed Filters







Graph Display Software for Author Relationships with Bibtex Files









3. Edges with lower weight than a threshold are removed.



