Software Defined Radio (SDR)

Software-defined radio (SDR) is a radio communication system where components that have been traditionally implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system. While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which were once only theoretically possible.

A basic SDR system may consist of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware (electronic circuits). Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.

Software radios have significant utility for the military and cell phone services, both of which must serve a wide variety of changing radio protocols in real time. In the long term, software-defined radios are expected by proponents like the Wireless Innovation Forum to become the dominant technology in radio communications. SDRs, along with software defined antennas are the enablers of the cognitive radio.

A software-defined radio can be flexible enough to avoid the “limited spectrum” assumptions of designers of previous kinds of radios, in one or more ways including:

  • Spread spectrum and ultrawideband techniques allow several transmitters to transmit in the same place on the same frequency with very little interference, typically combined with one or more error detection and correction techniques to fix all the errors caused by that interference.
  • Software defined antennas adaptively “lock onto” a directional signal, so that receivers can better reject interference from other directions, allowing it to detect fainter transmissions.
  • Cognitive radio techniques: each radio measures the spectrum in use and communicates that information to other cooperating radios, so that transmitters can avoid mutual interference by selecting unused frequencies. Alternatively, each radio connects to a geolocation database to obtain information about the spectrum occupancy in its location and, flexibly, adjusts its operating frequency and/or transmit power not to cause interference to other wireless services.
  • Dynamic transmitter power adjustment, based on information communicated from the receivers, lowering transmit power to the minimum necessary, reducing the near–far problem and reducing interference to others, and extending battery life in portable equipment.
  • Wireless mesh network where every added radio increases total capacity and reduces the power required at any one node. Each node transmits using only enough power needed for the message to hop to the nearest node in that direction, reducing the near–far problem and reducing interference to others.



some common low-cost DVB-T USB dongles with the Realtek RTL2832U controller and tuner, e.g. the Elonics E4000 or the Rafael Micro R820T, can be used as a wide-band (3 MHz) SDR receiver. Experiments proved the capability of this setup to analyze Perseids meteor shower using Graves radar signals. This project is being maintained at Osmocom.

GNU Radio using primarily the Universal Software Radio Peripheral (USRP) uses a USB 2.0 interface, an FPGA, and a high-speed set of analog-to-digital and digital-to-analog converters, combined with reconfigurable free software. Its sampling and synthesis bandwidth (30-120 MHz) is a thousand times that of PC sound cards, which enables wideband operation.

The HPSDR (High Performance Software Defined Radio) project uses a 16-bit 135 MSPS analog-to-digital converter that provides performance over the range 0 to 55 MHz comparable to that of a conventional analogue HF radio. The receiver will also operate in the VHF and UHF range using either mixer image or alias responses. Interface to a PC is provided by a USB 2.0 interface, although Ethernet could be used as well. The project is modular and comprises a backplane onto which other boards plug in. This allows experimentation with new techniques and devices without the need to replace the entire set of boards. An exciter provides 1/2 W of RF over the same range or into the VHF and UHF range using image or alias outputs.

WebSDR is a project initiated by Pieter-Tjerk de Boer providing access via browser to multiple SDR receivers worldwide covering the complete shortwave spectrum. Recently he has analyzed Chirp Transmitter signals using the coupled system of receivers.


Digital Radio Mondiale (DRM)

DRM is the universal, openly standardised digital broadcasting system for all broadcasting frequencies, including the AM bands (LW, MW, SW), as well as VHF Bands I, II – (FM band) and III.

DRM ensures the efficient and complete digitisation of those countries committing to the digital radio roll-out. The great flexibility of DRM supports all types of coverage needs – from local, regional, nation-wide to international.  DRM allows a seamless transition to digital radio with the upgrade of existing transmitter infrastructure as well as with analogue-digital simulcast configurations. DRM digital radio can save broadcasters up to 80% in energy and maintenance costs.

DRM Radio Frequencies

B.U.T.E (Budapest Hungary) – 26060 kHz

Funklust bitXpress (BIX) (Germany) – 15785 kHz

Radio France International (France) – 3965 kHz

BBC World Service (UK) – 3955 kHz

Shortwave frequencies are generally considered to be the portion of the radio spectrum between 1.7 MHz and 30 MHz (1705 KHz to 30,000 KHz). The frequencies between 525 KHz and 1705 KHz are medium wave.

For more informtion see:


1. Set the band to NFM

2. Go to Audio, then to Output and choose [Windows DirectSound] Cable Input (VB-Audio Virtual Cable).

3. Go to DSD Interface. Choose Audio device [Windows DirectSound] Cable Input (VB-Audio Virtual Cable).

4. Click Configure and go to DSD path. Go to your DSD folder and click on DSDPlus.exe. Click Open.

5 Under Decoder options to either Auto detect (default) or DMR/MotoTRBO.

6. Click Create command line, then click Ok.

Software required for decoding DRM with AIRSPY SDR:

  • DSDPlus
  • DSDPlus DLL Files
  • Virtual Audio Cable


SDR Links

Airspy is a line of Popular Software-Defined Radio (SDR) receivers developed to achieve High Performance and Affordable Price using innovative combinations of DSP and RF techniques.

DSDPlus is a Win32 application capable of reliably decoding multiple types of digital audio formats commonly found on VHF, UHF and 800 MHz.
This can be used in conjuction with other software to decode DRM radio.

GNU Radio
GNU Radio is a free software development toolkit that provides signal processing blocks to implement software-defined radios and signal-processing systems. It can be used with external RF hardware to create software-defined radio.

GNU Radio Wiki (Windows)
Information on GNU Radio software for Windows.

Gqrx SDR
Gqrx is an open source software defined radio receiver (SDR) powered by the GNU Radio and the Qt graphical toolkit.Available for Windows, Linux and Mac OS X.

Mac Ham Radio
Devoted to Amateur Radio Operators using Apple Mac OS X.

Osmocom (open source mobile communications) is an open-source software project that implements multiple mobile communication standards, including GSM, DECT, TETRA and others.

Software Defined Radio (SDR) is a Windows solution for Software Defined Radio (SDR) receivers and transceivers. Designed for the commercial, government, amateur radio and short-wave listener communities, this software provides a powerful interface for all SDR users.

VB-CABLE is a virtual audio device working as virtual audio cable. All audio coming in the CABLE input is simply forwarded to the CABLE output.
Available for Windows and Apple Mac.

WebSDR is a Software-Defined Radio receiver connected to the internet, allowing many listeners to listen and tune it simultaneously. SDR technology makes it possible that all listeners tune independently, and thus listen to different signals; this is in contrast to the many classical receivers that are already available via the internet.


Information & Tutorials

DATV Express software (YouTube)
Here we take a look at DATV Express software which lets you transmit digital video using an SDR such as the Lime SDR or Adalm Pluto.

Digital Radio Mondiale (DRM)
DRM is the universal, openly standardised digital broadcasting system for all broadcasting frequencies, including the AM bands (LW, MW, SW), as well as VHF Bands I, II – (FM band) and III.

DRAGON OS FOCAL – The Software Defined Radio Toolbox (YouTube)

DRM – Digital Radio Mondiale – Reception in New Zealand
This page documents some of the experimenting I have being doing with reception of digital shortwave broadcasts from my home in Wellington, New Zealand and my holiday cottage in Marahau, Tasman Bay, New Zealand. To date I have been able to receive broadcasts from transmitters located in the Netherlands Antilles, Canada, Portugal, the UK, Luxembourg, Morocco, Sri Lanka, Kuwait, Thailand, The Netherlands, Germany, Russia, China, France, Sweden, Norway, Chile, Austria, Spain, New Zealand, Australia, India, Ecuador, Bulgaria & Romania.

DRM Reception Project
specialise in the reception of DRM either via the Dream software, the legacy DRM Software Radio, the world-wide network of KiwiSDRs, or using standalone DRM radios.

Getting the RTL-SDR to work in Windows 10 (RTL-SDR.COM)
The RTL-SDR is fully compatible with Windows 10. However with the recent release of Windows 10 some users have been having trouble using their RTL-SDR after upgrading.

How to get started with Software Defined Radio on Mac OS X (Computerworld)
Tune in: Software Defined Radio on a Mac.

How To Setup SDR # Sharp To Decode DMR Digitial Using DSD Plus And An RTL SDR Receiver on Windows 10 (YouTube)

Inmarsat Decoding With A Simple Patch Antenna (YouTube)

RTL SDR Drivers On Windows 10 (YouTube)

Shortwave Schedule
List of shortwave broadcasts worldwide.

The Wiki Reference
This is the Open Reference Source, the Radio Communications Resource that any RadioReference user can edit. Please feel free to share your knowledge by contributing information.

The Ultimate Easy DSD+ Usage Guide – Decoding Digital RTL-SDR SDRPlay (YouTube)

Unitrunker, DSD+ Plus, & Virtual Cable Installation & Config for Digital Trunked Scanning (YouTube)

Share Button