Software-defined radio

This article is written for beginners, higher level material can be found on using the links below

Software defined radio is the means of listening to radio waves using the combination of low level hardware, and software processing. While non-SDR techniques use physical hardware to demodulate FM and AM, In SDR raw data from the receiver gets sent into the USB port, and software is used to control the modulation. The only drawbacks of SDR are bandwidth constraints and processing. Since uncompressed unmodulated data is coming through a PC interface (USB mostly), a high speed connection and a computer with decent specs is required. A Single RTL-SDR May use up to 3.4MB, CPU usage varies on the tuner software you use. Using software defined radio opposed to regular radio gives you the ability to see signals you would normally only hear. Your eyes can cover a very wide bandwidth of signals on a computer screen, while your ears can only comprehend a single spoken conversation at a time.

SDR models

SDRs come in many shapes in sizes, from the $8 RTL-SDR to $2000 USRP(with daughterboards) There are also many SDR's such as the HackRF, USRP, FunCube, etc.List of SDRs When you buy an SDR, you get what you pay for. More expensive SDR's are purpose built for receiving, and can handle things such as GSM spoofing, where an unencrypted GSM tower can be simulated to capture SMS in a cleartext fashion.

RTLSDR

A great beginner SDR is the RTL-SDR It features a receive frequency range of 25-1700MHz, 2.048MHz bandwidth and is priced low enough that beginners can see whether radio is a hobby they want to get into(R820T model).

RTL-SDRs come with various tuner chips, the most widely used tuner is the R820T, with the E4000 coming in a close second. The E4000 is a discontinued model and is usually priced higher than R820T models. R820T tuners are generally better for reception of trunked radio systems (digital police radio).

The RTLSDR began its life as a DVB-T OTA TV tuner (a tv tuner for europe). China began bulk manufacturing these TV tuners for the european market. It was later found that a hacked driver could be installed that let the user use the dongle as an SDR.

Currently R820T RTLSDRs can be bought for as low as $8 on eBay with free shipping R820Ts on eBay

HackRF

The HackRF is a DARPA funded project, it aims to provide innovation and research in the SDR field. It's much more powerful than the RTL-SDR, much more sensitive, covers a greater frequency range. The HackRF starts at $300, has both RX and TX functionality from 30 MHz to 6 GHz, bandwidth of 20MHz. During DARPA funding, beta units, the HackRF Jawbreaker were given to hundreds of testers for free. The production version was funded through KickStarter. The campaign was successfully funded on September 4th 2013 and will be available to the public after donators get their HackRF's. KickStarter Page

Transmitting

TX functionality on the HackRF is limited in power because RF theory says you must have an antenna length that corresponds to the wavelength you are sending. For example sending 5Watts over the wrong size antenna will cause a buildup of standing waves, and may fry the transmitter. To prevent this, the antenna build into the breadboard of the HackRF is only designed for ultra low power, good enough for experimentation, but not for serious broadcasting.

Possibilities

SDR's have endless possibilities. Because all demodulation is done in software, no new hardware is needed to decode, for example, a new digital voice mode. All the programmer has to do is write code to convert the raw samples from USB to the correct format data.

Software

Software is available for Windows GNU/Linux and OSX.

SDR Software (The stuff you listen with)

Software	Supported Modes	OS	Cost/License	Features/Limitations
SDR Touch	AM, WFM, NFM, SSB, DSB, CW	Android	Freemium, Closed	supports RTL_TCP and USB OTG, FFT times out after 30 seconds on free version
glSDR	AM, WFM, NFM, SSB, DSB, CW, DIG(?), SPEC(?), SAM(?), DRM	Android	Free, GNU/GPL	UI for ghpsdr servers
SDR-Radio		Windows	Free, Closed	Feature packed, harder to get set up
SDR-Radio v2		Windows	Free possibly paid out of beta, Closed	Beta, Feature packed, supports RTL_TCP
SDR#		Windows	Free, MS-RSL/MIT	Most popular and easiest to use
HD-SDR		Windows	Free, Closed
PowerSDR		Windows	Free, GNU/GPL	Does not support RTL-SDR
GQRX	AM, WFM, NFM, SSB, CW, AFSK1200	Win,Lin,Mac	Free, GNU/GPL	Runs on GNU Radio
GNU Radio		Win,Lin,Mac	Free, GNU/GPL	Tools to build your own receiver. Versatile, larger learning curve.
Linrad		Win,Lin,Mac	Free, OSS
Studio1			Paid,Closed Source	Formerly WRPLUS

Plugins for SDR#

Purpose	Software	Cost/License
Scan and log various frequencies	Frequency Manager + Scanner plugin	Free, OSS
Tune SDR# to the approprate voice channel	Trunking plugin for SDR#	Free, OSS

HF decoders (shortwave 0-30MHz)

Purpose	Mode	Software	OS	Cost/License	Common Frequency
Digital decoding on HF	CW, Domino, Hell, MFSK, PSK, OLIVIA, RTTY, Throb, Thor, WWV	Fldigi	Win,Lin,Mac	Free, GNU/GPL	0-30MHz AM
HF amateur radio codec	FreeDV, Codec2	FreeDV	Win,Lin,Mac	Free, GNU/GPL	0-30MHz AM
Digital broadcast shortwave	DRM	Dream	Win,Lin,Mac	Free, GNU/GPL	0-30MHz AM
Sending images over HF, commonly QSLs	Robot, AVT, Scottie, Martin	MMSSTV	Windows	Free, OSS	0-30MHz AM

ADS-B Airplane tracking software

Purpose	Mode	Software	OS	Cost/License	Frequency
Plane-spotting, decoding ADS-B	ADS-B	ADSB#	Windows	Free, MIT	1090MHz AM
Decodes ADSB# data + Plot planes on a map	AVR-BEAST	VirtualRadar Server	Windows	Free, OSS	1090MHz AM
Alternative to ADS-B#	ADS-B	RTL1090	Windows	Free, Closed	1090MHz AM

APRS (like GPS, hams use it)

Purpose	Mode	Software	OS	Cost/License	Frequency
Amateur packet radio incl. GPS location	AX.25, AFSK, APRS	AFSK1200	Win,Lin,Mac	Free, GNU/GPL	144-145MHz FM, Varies

Trunked Radio (police fire and EMS in urban areas)

Purpose	Mode	Software	OS	Cost/License	Frequency
Decode control channel data	P25, EDACS48, EDACS96, Motorola, MPT1327	Unitrunker	Windows	Free, Closed	Usually 400MHz, 760,860,933MHz FM
Decode digital voice	P25p1, ProVoice, X2-TDMA, DMR/MOTOTRBO, NXDN	DSD	Win,Lin,Mac	Free, BSD	Usually 400MHz, 760,860,933MHz FM
Decode LTR data	LTR	LTR Analyzer	Windows	Free, Unknown	~400-500MHz

NOAA weather satellite

Purpose	Mode	Software	OS	Cost/License	Frequency	Other
Decode NOAA WX images	APT, WEFAX	WxtoIMG	Win,Lin,Mac	Freemium, Closed	~137MHz FM	Track Live

Television (non digital kind)

Purpose	Mode	Software	OS	Cost/License	Frequency
Analog television decoder, no sound	NTSC, PAL	TVSharp	Windows	Free, OSS	Any AM (including ISM security cameras)

Pagers

Purpose	Mode	Software	OS	Cost/License	Frequency
Decode various pager formats	POCSAG, FLEX	PDW	Windows	Free, GNU/GPL	35-45MHz, 152-160MHz, 455-463MHz, 928-932MHz FM

Other SDR resources

/r/RTLSDR on Reddit

Scanner centric SDR discussion forums on RadioReference

FCC website, every RF transmitter registered registered with the FCC resides in this database

An online SDR receiver that covers the HF band (shortwave, worldwide transmissions)

Video Tutorials

SDRSharp (Windows)