We continue with the previous entry where we saw how to make a cheap SDR with a DTT receiver with Realtek RTL2832U chip seeing how to use it to capture RF signals from devices such as sensors or weather stations.
Let’s remember that in the previous entry we saw how to use a USB DTT receiver with RTL2832U chip that we can find for a price of about 6-7€, to capture signals along with SDR-Sharp program.
With that we could visualize RF signals in a band from 24MHz to 1850MHz. This includes, among others, RF signals from sensors, remote controls, weather stations, and a lot of domestic RF devices.
However, deciphering the captured code is somewhat laborious. In general terms, we must record the signal, export it, open it with a program like Audacity and reverse engineer the signal. A manual and tedious process.
Fortunately, there are several programs developed by the community that are going to avoid this work for us, and with which we can directly obtain the content of the decoded signal.
One of the most popular developments for decoding RF signals is RTL_433, which of course is compatible with the RTL2832U chip. RTL_433 can decode signals in a wide variety of formats and frequencies including 315 MHz, 345 MHz, 433.92 MHz, 868 MHz (SRD), and 915 MHz (ISM).
In addition, RTL_433 identifies a series of predefined signals. In most domestic devices, these signals are sufficient, and we can decode them without any additional requirements.
In case you are listening to a non-preconfigured device, RTL_433 also facilitates the export of the received signal to a ‘.cu8’ file, which we can then analyze, for example, with PulseView (which we already saw in this post).
Finally, we can also add our own signal definitions to those predefined in RTL_433. In the project documentation, you will find detailed instructions on the process.
This is how simple it is to receive and decode RF signals with a simple DTT receiver, the help of SDR-Sharp to detect signals, and RTL_433 to decode them.
RTL_433 is available for Windows, Linux, and MacOS. It is an Open Source project, and its code and documentation are available at https://github.com/merbanan/rtl_433.