Reading 433Mhz codes from computer with SDR and RTL_433

We continue from the previous post where we saw how to make a cheap SDR with a TV receiver with a Realtek RTL2832U chip, now seeing how to use it to capture RF signals from devices like sensors or weather stations.

Recall that in the previous post we saw how to use a USB TV receiver with an RTL2832U chip that can be found for a price of about 6-7€, to capture signals along with the SDR-Sharp program.

With that, we could visualize RF signals in a band from 24MHz to 1850MHz. This includes, among others, the RF signals from sensors, remote controls, weather stations, and a host of domestic RF devices.

However, deciphering the captured code is somewhat laborious. Broadly speaking, we need to 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 will save us this work, and with which we can directly obtain the decoded content of the 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).

Furthermore, RTL_433 identifies out of the box a large number of predefined signals. For most domestic devices, these signals are sufficient, and we will be able to decode them without any additional requirements.

In case you are listening to a device not preconfigured, RTL_433 also facilitates exporting the received signal to a ‘.cu8’ file, which we can later analyze, for example, with PulseView (which we already saw in this post).

Finally, we can also add our own signal definitions to the predefined ones in RTL_433. In the project documentation, you will find detailed instructions on the process.

That’s how easy it is to receive and decode RF signals with a simple TV receiver, the help of SDR-Sharp to detect signals, and RTL_433 to decode them.