Today we are going to see how to use a computer to receive radio frequency (RF) signals thanks to a simple and cheap DVB-T receiver that has the RTL2832U chip.
SDR, or Software Defined Radio, programs allow converting a computer into a radio frequency signal reception station, including wireless sensors, weather stations, and wireless remotes.
An SDR performs some of the tasks normally done by RF receiver hardware through software, avoiding the high cost of these components, with quite acceptable quality levels.
For this, we will simply need a DVB-T receiver with the RTL2832U chip and an R820T (Rafael Micro) as a tuner, which can be found for 6-7€ on eBay or AliExpress.
This small and cheap receiver, of which the image is one of several possible models, in its normal use serves to watch DVB-T channels and listen to radio on the computer.
But with a software change we will be able to convert it into an RF receiver for a frequency range from 24MHz to 1850MHz, with a bandwidth of up to 3.2 MHz sampling frequency, and compatible with AM, FM, WFM, NFM, USB, LSB, CW modes.
This covers almost the entire VHF and UHF range. Here are some of the frequencies we can receive.
| Band | Mhz | Mode |
|---|---|---|
| Shortwave | 24.5-28.5 | AM, USB, LSB, CW |
| Satellite | 29, 137, 145 | NFM, WFM, CW, SSB |
| FM Broadcast | 87-108 | WFM |
| ATC (Air Traffic Control) | 118-134 | AM |
| Services (taxis, etc) | 137-174 | NFM |
| Marine Band | 156-164 | NFM |
| 2m Band | 144-148 | NFM |
| 70cm Band | 430-440 | NFM |
| PMR (Walkie-Talkies) | 446-446.1 | NFM |
| ISM Band | 863-869.9 | NFM |
The topic of bands and modes alone could fill several posts. If you are interested, you can check information about amateur radio. It’s a wide and interesting world.
Installing SDRSharp
There are several SDR software options compatible with the RTL2832U. Undoubtedly the most popular is SDRSharp, which is free software available on the page https://airspy.com/download/
To install it, simply download the program file and extract its contents. Then run install-rtlsdr.bat to install SDRSharp.
Next, we need to replace the Windows drivers for the RTL2832U. For this, we will use the Zadig program available at https://zadig.akeo.ie/
Download Zadig and run it as administrator. Make sure to check “List all devices” in the options menu. Then, choose our device from the dropdown.
The name may vary, so we ensure the USB ID matches 0BDA:2838:00. Finally, click “Replace Driver” and wait for the program to replace the drivers.
Now we can launch SDRSharp. In the “Source” dropdown, choose RTL-SDR Usb. Then, click on the configuration icon (the gear). In the window that appears, choose our USB device.
We can now click PLAY and we will see how we start registering radio frequency emissions.
Now we can navigate to the frequency range of our environment, record and export the received emissions, and open them in another program. A simple audio editing program (like Audacity) can be enough to perform reverse engineering.
SDRSharp is a quite extensive and powerful program, with a wide variety of options. For more information, consult the documentation on its website.
Conclusion
Being able to receive RF signals from the computer is a very interesting functionality within the #maker field. For example, it is a great tool to analyze the operation of wireless sensors and transmitters in the 433MHz and 866MHz bands.
With a simple DVB-T receiver with the RTL2832U chip and the right software, we can have a fully functional analyzer for just 6-7€, with notable quality, and a considerably wide range from 24MHz to 1850MHz.
We have seen how to use the RTL2832U with the SDRSharp program to visualize RF signals in our environment. Although it is a very interesting program, the reverse engineering process requires some effort.
In the next post, we will see an alternative that will allow us to easily read 433MHz signals from most wireless sensors and remote controls. See you soon!
