RTL-SDR Introduction

Realtek introduced the DVB-T COFDM Demodulator + USB 2.0 RTL2832U in 2008. The main purpose of this chip and the same dongle of the same name was to receive TV in the DVB-T format. Moreover, the dongles based on the chip include  radio support (FM, DAB, DAB+). In contrast to the DVB-T demodulation that is processed on the chip, the radio demodulation occurs on the host. This feature was first noticed by Eric Fry in March of 2010 and then confirmed by Antti Palosaari in Feb 2012 who found by analysing the USB exchange between Host and USB device that the RTL2832U chip can output unsigned 8bit I/Q samples to the host. “I have taken radio sniffs from FM capable Realtek DVB-T device. Looks like demodulator ADC samples IF frequency and pass all the sampled data to the application. Application is then responsible for decoding that. Device supports DVB-T, FM and DAB. I can guess both FM and DAB are demodulated by software. I smell very cheap poor man’s software radio here :)”

RTL2832U has direct analogue input of I and Q signals from the tuner and depending on the tuner, supports the frequency range from 24 MHz to 2.200 GHz.The RTL2832U supports tuners at IF (Intermediate Frequency, 36.125MHz), low-IF (4.57MHz), or Zero-IF output using a 28.8MHz crystal.

Although Realtek did not publish a publicly available datasheet for this product, the wide frequency range and the low price provided a massive boost for the development of the software components for this chip and RTL-SDR dongles. A comprehensive list of the software components can be found on the RTL-SDR site.

Currently, the software components for the SDR uses only a fraction of functionalities available on the chip:

  • ADC
  • Infrared
  • I2C for the tuner management
  • GPIO

The main part of the chip (powerful OFDM-demodulator) is not used in the SDR at all.

The previous and current projects regarding RTL-SDR clock synchronisation are described in the section projects. The presented solutions are restricted to the maximum 3-4 dongles and cannot be extended.

Moreover, there are many hardware extensions that enable the use of such dongles in further applications, e.g.

  • Receiving navigation signals in the VLF – very low frequencies (3…30 kHz) and LF – low frequencies, 30…300 kHz );
  • Receiving of radio and ham stations in the LW, MW, SW ranges, e.g. DRM;
  • Receiving of aero messages in the 118…137 MHz;
  • Bandwidth monitoring and detection of radio jamming;
  • Multi-channel reception of sat signals (meteo data, ham satellites);
  • ADSB decoding and aircraft position tracking;
  • AIS decoding and maritime vessels position tracking.

These hardware extensions are not standardised and every solution has its own form-factors, connection requirements, etc. The main target group of the hardware extensions are radio hobbyists or radio amateurs. You can find a more detailed discussion on the hardware extensions to the RTL-SDR in the section Extension Cards.

Current SDR Research Activities

All research activities can be divided into the following main areas:

  • Projects: for coherent receiving using the RTL-SDR technology. We do not plan to remain confined whithin the RTL-SDR technology in the future and would like to provide coherent solutions for other software defined radio systems.
  • Publications: We monitor the publication of the software defined radio technologies, coherent receiving and application scenarios that use these technologies.
  • Patents: We analyse the latest patents in the Software Defined Radio area, coherent receiving, radar and antenna array technologies.

Please contact us, if you are working or doing research in the above mentioned areas and would like to present your publications, projects, or patents. We offer support for researchers from the hardware point of view. Therefore, feel free to inquire about additional requirements, explanations or simply to discuss some ideas on how to use these technologies in your research area.