If we talk a little about the kinds of receivers that we can buy in the market, few years ago we only have one option: to buy a so expensive device that receive in a perfect way but does not give us anything else.
Nowadays we have another option: to buy a low cost SDR receiver that gives us a wide frequency range that allows us to get ADS-B messages but not only this. It brings us the opportunity to receive in some other frequencies like FM radio, ATC live control, aeronautical ACARS messages, etc.
As we can see the prices of the two devices there is any question of which most of us will choose.
OUR GOAL: Build a similar scenario by using cheap devices able to receive and decode ADS-B information and plot it in real-time.
What is SDR?
SDR stands for Software Defined Radio and is a radio communication system where components are implemented in software; different from it is supposed to be.
SDR can be generically defined as a radio that uses software techniques on digitized radio signals. The fundamental intent is to shift from employing a traditional hardware-focused system to a radio implementation using a software application to perform the radio tasks on a computing platform. The digitization is near the antenna and all the processing is performed by software residing in high-speed digital signal processing functionality.
The concept of independence between the acquisition step and the processing steps is the clearest definition of an SDR system.
This table shows us the comparison of different receivers and their characteristics:
|SDR||Tune Low (MHz)||Tune Max (MHz)||RX Sample Rate (MHz)||ADC Resolution (Bits)||Transmit?(Yes/No)||
300 – 480
Our purpose was to receive, process and get the data at every moment and to situate our scenario, which must consist of an USB dongle, a computer or a laptop to process the data and internet connection to send this data to webs or just to create a web server to visualize all the information.
And the solution to all of these purposes is the raspberry pi. The raspberry pi is a little computer that allows us to leave our system in a lot of places, that is give us the flexibility that needs a system like this for many reasons. The main reason is to situate the antenna in a good place to receive as much as possible frames from the aircrafts of the surroundings.
CHARACTERISTICS OF THE RASPBERRY PI:
- Small computer.
- Low cost, aproximately 25€.
- HDMI connection, 2 USB ports, SD card memory system, ethernet connection, microUSB power supply, video output, etc.
- Low consumption, it can be connected all the day with only 1€ cost over 1 month.
- It can be accessed remotely.
- It runs a debian version for this specific hardware.
The raspberry pi gives us a lot of powerful characteristics this is, by the way, the reason why we have used this small computer to process the data of the RTL-SDR dongle.
The Raspberry Pi is a credit-card-sized single-board computer developed in the UK by the Raspberry Pi Foundation with the intention of promoting the teaching of basic computer science in schools.
The Raspberry Pi has a Broadcom BCM2835 system on a chip (SoC), which includes an ARM1176JZF-S 700 MHz processor, VideoCore IV GPU and was originally shipped with 256 MB of RAM, later upgraded to 512 MB. It uses an SD card for booting and long-term storage. The Foundation’s goal was to offer two versions, priced at $25 (model A) and $35 (model B). They started accepting orders for the higher priced model B on 29 February 2012, and the lower cost model A on 4 February 2013.
The Foundation provides Debian and Arch Linux ARM distributions for download. Also planned are tools for supporting Python as the main programming language.