Editing Software-defined radio

{{Short description|Radio communication system implemented in software}}
{{Multiplex techniques}}
{{Modulation techniques}}

'''Software-defined radio''' ('''SDR''') is a [[radio]] communication system where components that conventionally have been implemented in [[Analogue electronics|analog]] hardware (e.g. [[frequency mixer|mixer]]s, [[Filter (signal processing)|filter]]s, [[amplifier]]s, [[modulator]]s/[[demodulator]]s, [[detector (radio)|detector]]s, etc.) are instead implemented by means of software on a computer or [[embedded system]].<ref>{{Cite book|title=Software Defined Radio: Architectures, Systems and Functions|author=Markus Dillinger |author2=Kambiz Madani |author3=Nancy Alonistioti |page=xxxiii |publisher=Wiley & Sons|year= 2003|isbn=0-470-85164-3}}</ref>

A basic SDR system may consist of a [[personal computer|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 circuit]]s). 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 antenna]]s are the enablers of [[cognitive radio]].<ref>{{Cite book|last=Amaral|first=Cristiano|title=Guia Moderno do Radioescuta|publisher=Amazon|year=2021|isbn=978-65-00-20800-9|location=Brazil|page=333}}</ref>

== Operating principles ==
[[File:SDR et WF.svg|thumb|right|upright=1.8|Software defined radio concept]]

[[Superheterodyne receiver]]s use a VFO ([[variable-frequency oscillator]]), [[Frequency mixer|mixer]], and [[Filter (signal processing)|filter]] to tune the desired signal to a common IF ([[intermediate frequency]]) or [[baseband]]. Typically in SDR, this signal is then sampled by the analog-to-digital converter. However, in some applications it is not necessary to tune the signal to an intermediate frequency and the radio frequency signal is directly sampled by the [[analog-to-digital converter]] (after amplification).

Real analog-to-digital converters lack the dynamic range to pick up sub-microvolt, nanowatt-power radio signals produced by an antenna. Therefore, a [[low-noise amplifier]] must precede the conversion step and this device introduces its own problems. For example, if [[Spurious emission|spurious signals]] are present (which is typical), these compete with the desired signals within the amplifier's [[dynamic range]]. They may introduce distortion in the desired signals, or may block them completely. The standard solution is to put [[band-pass filter]]s  between the antenna and the amplifier, but these reduce the radio's flexibility. Real software radios often have two or three analog channel filters with different bandwidths that are switched in and out.

The flexibility of SDR allows for dynamic spectrum usage, alleviating the need to statically assign the scarce spectral resources to a single fixed service.<ref>{{Cite journal |url=http://www.spectrum.ieee.org/mar04/3811 |archive-url=https://archive.today/20120910051620/http://www.spectrum.ieee.org/mar04/3811 |url-status=dead |archive-date=September 10, 2012 |first1=Gregory |last1=Staple |first2=Kevin |last2=Werbach |title=The End of Spectrum Scarcity |journal=[[IEEE Spectrum]] |date=March 2004|volume=41 |issue=3 |pages=48–52 |doi=10.1109/MSPEC.2004.1270548 |s2cid=1667310 |url-access=subscription }}</ref>

== History ==
In 1970, a researcher{{who|date=August 2022}} at a [[United States Department of Defense]] laboratory coined the term "digital receiver". A laboratory called the Gold Room at [[TRW Inc.|TRW]] in California created a software baseband analysis tool called Midas, which had its operation defined in software.{{fact|date=August 2022}}

In 1982, while working under a US Department of Defense contract at [[RCA]], [[Ulrich L. Rohde]]'s department developed the first SDR, which used the [[RCA 1802|COSMAC]] (Complementary Symmetry Monolithic Array Computer) chip. Rohde was the first to present on this topic with his February 1984 talk, "Digital HF Radio: A Sampling of Techniques" at the Third International Conference on HF Communication Systems and Techniques in London.<ref>{{Cite web |title=Ulrich Rohde, N1UL, Recognized for Pioneering Work on SDR |url=https://www.arrl.org/news/ulrich-rohde-n1ul-recognized-for-pioneering-work-on-sdr |access-date=2024-01-10 |date=2017-01-17 |publisher=[[American Radio Relay League]]}}</ref>

In 1984, a team at the [[Garland, Texas]], Division of [[E-Systems]] Inc. (now [[Raytheon]]) coined the term "software radio" to refer to a digital baseband receiver, as published in their E-Team company newsletter. A 'Software Radio Proof-of-Concept' laboratory was developed by the E-Systems team that popularized Software Radio within various government agencies. This 1984 Software Radio was a digital [[baseband]] receiver that provided programmable interference cancellation and demodulation for broadband signals, typically with thousands of [[adaptive filter]] taps, using multiple [[array processor]]s accessing shared memory.<ref>{{cite journal|first1=P.|last1= Johnson|title=New Research Lab Leads to Unique Radio Receiver|journal= E-Systems Team|date=May 1985|volume= 5|issue= 4|pages= 6–7|url= http://chordite.com/team.pdf}}</ref>

In 1991, Joe Mitola independently reinvented the term software radio for a plan to build a [[GSM]] base station that would combine Ferdensi's digital receiver with E-Systems Melpar's digitally controlled communications jammers for a true software-based transceiver. E-Systems Melpar sold the software radio idea to the US Air Force. Melpar built a prototype commanders' tactical terminal in 1990–1991 that employed [[Texas Instruments]] [[Texas Instruments TMS320|TMS320C30]] processors and [[Harris Corporation]] digital receiver chip sets with digitally synthesized transmission. The Melpar prototype didn't last long because when E-Systems ECI Division manufactured the first limited production units, they decided to "throw out those useless C30 boards", replacing them with conventional RF filtering on transmit and receive and reverting to a digital baseband radio instead of the SpeakEasy like IF ADC/DACs of Mitola's prototype. The Air Force would not let Mitola publish the technical details of that prototype, nor would they let Diane Wasserman publish related software life cycle lessons learned because they regarded it as a "USAF competitive advantage".{{fact|date=August 2022}} So instead, with USAF permission, in 1991, Mitola described the architecture principles without implementation details in a paper, "Software Radio: Survey, Critical Analysis and Future Directions" which became the first [[IEEE]] publication to employ the term in 1992.<ref>{{Cite conference |first=J. |last=Mitola III |title=Software radios-survey, critical evaluation and future directions |conference=National Telesystems Conference |year=1992 |pages= 13/15 to 13/23 |isbn=0-7803-0554-X |doi=10.1109/NTC.1992.267870 }}</ref> When Mitola presented the paper at the conference, Bob Prill of [[Marconi Electronic Systems|GEC Marconi]] began his presentation following Mitola with: "Joe is absolutely right about the theory of a software radio and we are building one."{{fact|date=August 2022}} Prill gave a GEC Marconi paper on PAVE PILLAR, a SpeakEasy precursor.  SpeakEasy, the military software radio was formulated by Wayne Bonser, then of [[Rome Air Development Center]] (RADC), now Rome Labs; by Alan Margulies of [[Mitre Corporation|MITRE]] Rome, NY; and then Lt Beth Kaspar, the original DARPA SpeakEasy project manager and by others at Rome including Don Upmal. Although Mitola's IEEE publications resulted in the largest global footprint for software radio, Mitola privately credits that DoD lab of the 1970s with its leaders Carl, Dave, and John with inventing the digital receiver technology on which he based software radio once it was possible to transmit via software.{{fact|date=August 2022}}

A few months after the National Telesystems Conference 1992, in an E-Systems corporate program review, a vice-president of E-Systems Garland Division objected to Melpar's (Mitola's) use of the term "software radio" without credit to Garland. Alan Jackson, Melpar VP of marketing at that time, asked the Garland VP if their laboratory or devices included transmitters. The Garland VP said: "No, of course not&nbsp;— ours is a software radio receiver." Al replied: "Then it's a digital receiver but without a transmitter, it's not a software radio." Corporate leadership agreed with Al, so the publication stood. Many amateur radio operators and HF radio engineers had realized the value of digitizing HF at RF and of processing it with Texas Instruments TI C30 [[digital signal processor]]s (DSPs) and their precursors during the 1980s and early 1990s. Radio engineers at [[Roke Manor Research|Roke Manor]] in the UK and at an organization in Germany had recognized the benefits of ADC at the RF in parallel. Mitola's publication of software radio in the IEEE opened the concept to the broad community of radio engineers. His May 1995 special issue of the [[IEEE Communications Magazine]] with the cover "Software Radio" was regarded as a watershed event with thousands of academic citations. Mitola was introduced by Joao da Silva in 1997 at the First International Conference on Software Radio as "godfather" of software radio in no small part for his willingness to share such a valuable technology "in the public interest".{{fact|date=August 2022}}

Perhaps the first software-based radio [[transceiver]] was designed and implemented by Peter Hoeher and Helmuth Lang at the German Aerospace Research Establishment ([[German Aerospace Center|DLR]], formerly [[DFVLR]]) in [[Oberpfaffenhofen]], Germany, in 1988.<ref>P. Hoeher and H. Lang, "Coded-8PSK modem for fixed and mobile satellite services based on DSP," in Proc. First Int. Workshop on Digital Signal Processing Techniques Applied to Space Communications, ESA/ ESTEC, Noordwijk, Netherlands, Nov. 1988;  ESA WPP-006, Jan. 1990, pp. 117-123.</ref> Both transmitter and receiver of an adaptive digital satellite modem were implemented according to the principles of a software radio, and a flexible hardware periphery was proposed.{{fact|date=August 2022}}

In 1995, Stephen Blust coined the term "software defined radio", publishing a request for information from Bell South Wireless at the first meeting of the Modular Multifunction Information Transfer Systems (MMITS) forum in 1996 (in 1998 the name was changed to the Software Defined Radio Forum), organized by the USAF and DARPA around the commercialization of their SpeakEasy II program. Mitola objected to Blust's term, but finally accepted it as a pragmatic pathway towards the ideal software radio. Although the concept was first implemented with an IF ADC in the early 1990s, software-defined radios have their origins in the U.S. and European defense sectors of the late 1970s (for example, Walter Tuttlebee described a [[very low frequency|VLF radio]] that used an ADC and an [[Intel 8085|8085 microprocessor]]),<ref>First International Workshop on Software Radio, Greece 1998</ref> about a year after the First International Conference in Brussels. One of the first public software radio initiatives was the U.S. DARPA-Air Force [[military]] project named [[SpeakEasy]]. The primary goal of the SpeakEasy project was to use programmable processing to emulate more than 10 existing military radios, operating in [[frequency]] [[band (radio)|bands]] between 2 and 2000 [[Megahertz|MHz]].<ref>RJ Lackey and DW Upmal contributed the article "Speakeasy: The Military Software Radio" to the IEEE Communications Magazine special issue that Mitola edited and for which Mitola wrote the lead article "Software Radio Architecture", in May 1995.</ref> Another SpeakEasy design goal was to be able to easily incorporate new [[Channel coding|coding]] and modulation standards in the future, so that military communications can keep pace with advances in coding and modulation techniques.{{fact|date=August 2022}}

{{anchor|Digiceiver}}In 1997, [[Blaupunkt]] introduced the term "DigiCeiver" for their new range of DSP-based tuners with [[Sharx]] in [[car radio]]s such as the Modena & Lausanne RD&nbsp;148.

=== SpeakEasy phase I ===
From 1990 to 1995, the goal of the [[SpeakEasy]] program was to demonstrate a radio for the [[U.S. Air Force]] tactical ground air control party that could operate from 2 [[megahertz|MHz]] to 2 [[gigahertz|GHz]], and thus could interoperate with ground force radios (frequency-agile [[VHF]], [[frequency modulation|FM]], and [[SINCGARS]]), Air Force radios (VHF [[Amplitude modulation|AM]]), Naval Radios (VHF [[Amplitude modulation|AM]] and [[high frequency|HF]] [[single-sideband modulation|SSB]] [[teleprinter]]s) and [[communications satellite|satellites]] ([[microwave]] [[quadrature amplitude modulation|QAM]]).  Some particular goals were to provide a new signal format in two weeks from a standing start, and demonstrate a radio into which multiple contractors could plug parts and software.{{fact|date=August 2022}}

The project was demonstrated at [[Transformation of the United States Army#Force XXI|TF-XXI Advanced Warfighting Exercise]], and demonstrated all of these goals in a non-production radio. There was some discontent with failure of these early software radios to adequately filter out of band emissions, to employ more than the simplest of interoperable modes of the existing radios, and to lose connectivity or crash unexpectedly. Its [[cryptography|cryptographic]] processor could not change context fast enough to keep several radio conversations on the air at once. Its software architecture, though practical enough, bore no resemblance to any other. The SpeakEasy architecture was refined at the MMITS Forum between 1996 and 1999 and inspired the DoD integrated process team (IPT) for programmable modular communications systems (PMCS) to proceed with what became the Joint Tactical Radio System (JTRS).{{fact|date=August 2022}}

The basic arrangement of the radio [[receiver (radio)|receiver]] used an [[antenna (electronics)|antenna]] feeding an [[amplifier]] and down-converter (see [[Frequency mixer]]) feeding an [[automatic gain control]], which fed an [[analog-to-digital converter]] that was on a computer [[VMEbus]] with a lot of [[digital signal processor]]s ([[Texas Instruments]] C40s). The transmitter had [[digital-to-analog converter]]s on the [[PCI bus]] feeding an up converter (mixer) that led to a power amplifier and antenna. The very wide frequency range was divided into a few sub-bands with different analog radio technologies feeding the same analog to digital converters. This has since become a standard design scheme for wideband software radios.{{fact|date=August 2022}}

=== SpeakEasy phase II ===
The goal was to get a more quickly reconfigurable architecture, ''i.e.'', several conversations at once, in an ''open'' software architecture, with cross-channel connectivity (the radio can "bridge" different radio protocols). The secondary goals were to make it smaller, cheaper, and weigh less.{{fact|date=August 2022}}

The project produced a demonstration radio only fifteen months into a three-year research project. This demonstration was so successful that further development was halted, and the radio went into production with only a 4&nbsp;MHz to 400&nbsp;MHz range.{{fact|date=August 2022}}

The software architecture identified standard interfaces for different modules of the radio: "radio frequency control" to manage the analog parts of the radio, "modem control" managed resources for [[modulation]] and [[demodulation]] schemes (FM, AM, SSB, QAM, etc.), "waveform processing" modules actually performed the [[modem]] functions, "key processing" and "cryptographic processing" managed the cryptographic functions, a "multimedia" module did voice processing, a "human interface" provided local or remote controls, there was a "routing" module for network services, and a "control" module to keep it all straight.{{fact|date=August 2022}}

The modules are said to communicate without a central operating system. Instead, they send messages over the [[Peripheral Component Interconnect|PCI]] [[computer bus]] to each other with a layered protocol.{{fact|date=August 2022}}

As a military project, the radio strongly distinguished "red" (unsecured secret data) and "black" (cryptographically-secured data).{{fact|date=August 2022}}

The project was the first known to use [[FPGA]]s (field programmable gate arrays) for digital processing of radio data. The time to reprogram these was an issue limiting application of the radio. Today, the time to write a program for an FPGA is still significant, but the time to download a stored FPGA program is around 20 milliseconds. This means an SDR could change transmission protocols and frequencies in one fiftieth of a second, probably not an intolerable interruption for that task.{{fact|date=August 2022}}

=== 2000s ===
The SpeakEasy SDR system in the 1994 uses a [[Texas Instruments TMS320|Texas Instruments TMS320C30]] [[CMOS]] [[digital signal processor]] (DSP), along with several hundred [[integrated circuit]] chips, with the radio filling the back of a truck. By the late 2000s, the emergence of [[RF CMOS]] technology made it practical to scale down an entire SDR system onto a single [[mixed-signal]] [[system-on-a-chip]], which [[Broadcom]] demonstrated with the BCM21551 processor in 2007. The Broadcom BCM21551 has practical commercial applications, for use in [[3G]] [[mobile phones]].<ref>{{cite conference |last1=Leenaerts |first1=Domine |title=Wide band RF CMOS circuit design techniques |url=https://ewh.ieee.org/r5/denver/sscs/Presentations/2010_05_Leenaerts.pdf |conference=[[IEEE Solid-State Circuits Society]] Distinguished Lecturers Program (SSCS DLP) |publisher=[[NXP Semiconductors]] |date=May 2010 |access-date=10 December 2019}}</ref><ref>{{cite web |title=Broadcom ships "3G phone on a chip" |url=https://linuxdevices.org/broadcom-ships-3g-phone-on-a-chip/ |website=The LinuxDevices Archive |access-date=12 December 2019 |date=16 October 2007}}</ref>

== Military usage ==

=== United States ===
The [[Joint Tactical Radio System]] (JTRS) was a program of the US military to produce radios that provide flexible and interoperable communications. Examples of radio terminals that require support include hand-held, vehicular, airborne and dismounted radios, as well as base-stations (fixed and maritime).

This goal is achieved through the use of SDR systems based on an internationally endorsed open [[Software Communications Architecture]] (SCA). This standard uses [[CORBA]] on [[POSIX]] operating systems to coordinate various software modules.

The program is providing a flexible new approach to meet diverse soldier communications needs through software programmable radio technology. All functionality and expandability is built upon the SCA.

The SCA, despite its military origin, is under evaluation by commercial radio vendors for applicability in their domains. The adoption of general-purpose SDR frameworks outside of military, intelligence, experimental and amateur uses, however, is inherently hampered by the fact that civilian users can more easily settle with a fixed architecture, optimized for a specific function, and as such more economical in mass market applications. Still, software defined radio's inherent flexibility can yield substantial benefits in the longer run, once the fixed costs of implementing it have gone down enough to overtake the cost of iterated redesign of purpose built systems. This then explains the increasing commercial interest in the technology.

SCA-based infrastructure software and rapid development tools for SDR education and research are provided by the Open Source SCA Implementation{{snd}} Embedded (OSSIE<ref>{{cite web|url=http://ossie.wireless.vt.edu|title=OSSIE|work=vt.edu|archive-url=https://web.archive.org/web/20090312002811/http://ossie.wireless.vt.edu/|archive-date=2009-03-12}}</ref>) project. The Wireless Innovation Forum funded the SCA Reference Implementation project, an open source implementation of the SCA specification. ([[Software Communications Architecture Reference Implementation|SCARI]]) can be downloaded for free.

== Amateur and home use ==
[[File:Perseus SDR receiver.jpg|thumb|right|Microtelecom Perseus – an HF SDR for the amateur radio market]]
A typical [[amateur radio|amateur]] software radio uses a [[direct conversion receiver]]. Unlike direct conversion receivers of the more distant past, the mixer technologies used are based on the quadrature sampling detector and the quadrature sampling exciter.<ref>{{Citation |last=Youngblood |first=Gerald |title=A Software Defined Radio for the Masses, Part 1 |journal=[[QEX]] |pages=1–9 |publisher=[[American Radio Relay League]] |date=July 2002 |url=https://www.arrl.org/files/file/Technology/tis/info/pdf/020708qex013.pdf }}</ref><ref>{{Citation |last=Youngblood |first=Gerald |title=A Software Defined Radio for the Masses, Part 2 |journal=[[QEX]] |pages=10–18 |publisher=[[American Radio Relay League]] |date=Sep–Oct 2002 |url=http://www.arrl.org/files/file/Technology/tis/info/pdf/020910qex010.pdf }}</ref><ref>{{Citation |last=Youngblood |first=Gerald |title=A Software Defined Radio for the Masses, Part 3 |journal=[[QEX]] |pages=1–10 |publisher=[[American Radio Relay League]] |date=Nov–Dec 2002 |url=http://www.arrl.org/files/file/Technology/tis/info/pdf/021112qex027.pdf }}</ref><ref>{{Citation |last=Youngblood |first=Gerald |title=A Software Defined Radio for the Masses, Part 4 |journal=[[QEX]] |pages=20–31 |publisher=[[American Radio Relay League]] |date=Mar–Apr 2003 |url=http://www.arrl.org/files/file/Technology/tis/info/pdf/030304qex020.pdf }}</ref>

The receiver performance of this line of SDRs is directly related to the dynamic range of the analog-to-digital converters (ADCs) utilized.<ref>{{cite magazine|author=Rick Lindquist|author2=Joel R. Hailas |url=http://www.redorbit.com/news/technology/258812/flexradio_systems_sdr1000_hfvhf_software_defined_radio_redux/index.html|title=FlexRadio Systems; SDR-1000 HF+VHF Software Defined Radio Redux|magazine=[[QST]]|date=October 2005 |access-date=2008-12-07}}</ref>  Radio frequency signals are down converted to the audio frequency band, which is sampled by a high performance audio frequency ADC. First generation SDRs used a 44&nbsp;kHz PC sound card to provide [[Analog-to-digital converter|ADC]] functionality. The newer software defined radios use embedded high performance ADCs that provide higher [[dynamic range]] and are more resistant to noise and RF interference.

A fast PC performs the [[digital signal processing]] (DSP) operations using software specific for the radio hardware.  Several software radio implementations use the open source SDR library DttSP.<ref>[http://dttsp.sourceforge.net/ DttSP on Source Forge]</ref>

The SDR software performs all of the demodulation, filtering (both radio frequency and audio frequency), and signal enhancement (equalization and binaural presentation).  Uses include every common amateur modulation: [[morse code]], [[single-sideband modulation]], [[frequency modulation]], [[amplitude modulation]], and a variety of digital modes such as [[radioteletype]], [[slow-scan television]], and [[packet radio]].<ref>http://sourceforge.net/projects/sdr Open source SDR transceiver project using USRP and GNU Radio</ref> Amateurs also experiment with new modulation methods: for instance, the [[Digital Radio Mondiale#DRM software|DREAM]] [[Open-source software|open-source]] project decodes the [[COFDM]] technique used by [[Digital Radio Mondiale]].

There is a broad range of hardware solutions for radio amateurs and home use. There are professional-grade transceiver solutions, e.g. the Zeus ZS-1<ref>[http://zs-1.ru ZS-1 Project]</ref><ref>[http://www.radioaficion.com/HamNews/articles/9483-zeus-zs-1-sdr-transceiver.html ZS-1 Zeus Transceiver]</ref> or FlexRadio,<ref>Flex Radio SDR Transceivers http://www.flex-radio.com/</ref> home-brew solutions, e.g. PicAStar transceiver, the SoftRock SDR kit,<ref>SoftRock SDR Kits http://wb5rvz.com/sdr/</ref> and starter or professional receiver solutions, e.g. the FiFi SDR<ref>FiFi SDR Receiver http://o28.sischa.net/fifisdr/trac</ref> for shortwave, or the Quadrus coherent multi-channel SDR receiver<ref>[http://spectrafold.com/quadrus Quadrus coherenet multi-channel SDR receiver]</ref> for short wave or VHF/UHF in direct digital mode of operation.

=== RTL-SDR ===
[[File:DVB-T USB dongle with RTL2832U and R820T.jpg|thumb|Internals of a low-cost [[DVB-T]] USB dongle that uses Realtek RTL2832U (square IC on the right) as the controller and Rafael Micro R820T (square IC on the left) as the tuner]]

Eric Fry discovered that some common low-cost [[DVB-T]] USB dongles with the Realtek RTL2832U<ref>Using DVB USB Stick as SDR Receiver http://sdr.osmocom.org/trac/wiki/rtl-sdr</ref><ref>RTL-SDR Blog http://www.rtl-sdr.com</ref> controller and tuner, e.g. the Elonics E4000 or the Rafael Micro R820T,<ref>Support for the Rafael Micro R820T tuner in Cocoa Radio https://housedillon.com/blog/support-for-the-rafael-micro-r820t-tuner-o-cocoa-radio/</ref> can be used as a wide-band (3&nbsp;MHz) SDR receiver. Experiments proved the capability of this setup to analyze [[Perseids|Perseids meteor shower]] using [[Graves (system)|Graves radar]] signals.<ref>{{cite web|url=http://www.eb3frn.net/?p=141|title=Perseids shower using graves radar|work=EB3FRN|date=7 October 2013 }}</ref> This project is being maintained by the [[Osmocom]] project.

=== HPSDR ===
The [[HPSDR]] (High Performance Software Defined Radio) project uses  a 16-bit {{nowrap|135 MSPS}} analog-to-digital converter that provides performance over the range 0 to {{nowrap|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 [[Universal Serial Bus|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 [[Transmitter#Power output|exciter]] provides {{nowrap|1/2 W}} of RF over the same range or into the VHF and UHF range using image or alias outputs.<ref name="hpsdrhomepage">{{cite web|url=http://openhpsdr.org/ | title=HPSDR Web Site}}</ref>

=== WebSDR ===
WebSDR<ref>WebSDR http://websdr.org</ref> is a project initiated by Pieter-Tjerk de Boer providing access via browser to multiple SDR receivers worldwide covering the complete shortwave spectrum. De Boer has analyzed [[Chirp Transmitter]] signals using the coupled system of receivers.<ref>Chirp Signals analyzed using SDR http://websdr.ewi.utwente.nl:8901/chirps/</ref>

=== KiwiSDR ===
KiwiSDR<ref>{{Cite web |title=KiwiSDR |url=http://www.kiwisdr.com }}</ref> is also a via-browser SDR like WebSDR. Unlike WebSDR, the frequency is limited to 3 Hz to 30 MHz ([[Extremely low frequency|ELF]] to [[High frequency|HF]])

== Other applications ==
On account of its increasing accessibility, with lower cost hardware, more software tools and documentation, the applications of SDR have expanded past their primary and historic use cases. SDR is now being used in areas such as wildlife tracking, radio astronomy, medical imaging research, and art.

== See also ==
{{Portal|Radio|Telecommunication}}

* [[List of software-defined radios]]
* [[List of amateur radio software]]
* [[Digital radio]]
* [[Digital signal processing]] (DSP)
* [[Radio Interface Layer]] (RIL)
* [[Softmodem]]
* [[Software defined mobile network]] (SDMN)
* [[Software GNSS Receiver]]
* [[White space (radio)]]
* [[TV White Space Database|White space (database)]]
* [[Bit banging]]

== References ==
{{Reflist|30em}}

== Further reading ==
* {{ cite journal | first = Ulrich L | last = Rohde | title = Digital HF Radio: A Sampling of Techniques | journal = Third International Conference on HF Communication Systems and Techniques | location = London, England | date = February 26–28, 1985 }}
* ''Software defined radio : architectures, systems, and functions.'' Dillinger, Madani, Alonistioti. Wiley, 2003. 454 pages. {{ISBN|0-470-85164-3}} {{ISBN|9780470851647}}
* ''Cognitive Radio Technology.'' Bruce Fette. Elsevier Science & Technology Books, 2006.  656 pags. {{ISBN|0-7506-7952-2}} {{ISBN|9780750679527}}
* ''Software Defined Radio for 3G,'' Burns. Artech House, 2002. {{ISBN|1-58053-347-7}}
* ''Software Radio: A Modern Approach to Radio Engineering,'' Jeffrey H. Reed. Prentice Hall PTR, 2002. {{ISBN|0-13-081158-0}}
* ''Signal Processing Techniques for Software Radio,'' Behrouz Farhang-Beroujeny. LuLu Press.
* ''RF and Baseband Techniques for Software Defined Radio,'' Peter B. Kenington. Artech House, 2005, {{ISBN|1-58053-793-6}}
* ''The ABC's of Software Defined Radio,'' Martin Ewing, AA6E. The American Radio Relay League, Inc., 2012, {{ISBN|978-0-87259-632-0}}
* ''Software Defined Radio using MATLAB & Simulink and the RTL-SDR,'' R Stewart, K Barlee, D Atkinson, L Crockett, Strathclyde Academic Media, September 2015. {{ISBN|978-0-9929787-2-3}}

== External links ==
{{Commons category|Software defined radios}}

* [http://websdr.ewi.utwente.nl:8901/ The world's first web-based software-defined receiver] at the university of Twente, the Netherlands
* [http://www.websdr.org/ Software-defined receivers connected to the Internet]
* [https://www.ab9il.net/software-defined-radio/rtl2832-sdr.html Using software-defined television tuners as multimode HF / VHF / UHF receivers]
* [http://www.desktopSDR.com Free SDR textbook: Software Defined Radio using MATLAB & Simulink and the RTL-SDR]
* {{web archive |url=https://web.archive.org/web/20230223175232/https://www.robertputt.co.uk/welcome-to-the-world-of-software-defined-radio/ |title=Welcome to the World of Software Defined Radio}}
* [https://techxplore.com/news/2023-11-low-cost-testbed-terahertz-technology.html Software Defined Terahertz Radio] at Polytechnique Montreal, Canada
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