Also known as: SDR#, SDRSharp, SDR Sharp
SDR# (pronounced “SDR Sharp”, stylized SDRSharp) is a widely used Windows software-defined radio receiver application, written in .NET and maintained by the Airspy team.1 It presents a live spectrum and waterfall display, a tuning dial, and demodulators for the common analog modes, and it is a common first application for newcomers pairing a cheap RTL-SDR dongle with a PC. Its clean interface and rich plugin ecosystem made it one of the most recognizable SDR programs.
How it works
SDR# reads a stream of IQ samples from a front end, runs a fast Fourier transform for the spectrum and waterfall, and applies a selected demodulator to the slice of spectrum under the tuning marker. Users pick the mode (WFM, NFM, AM, single sideband, CW, raw), set the bandwidth of the receive filter, and adjust gain; the audio is played out the sound card or piped to another program via a virtual audio cable.
Front-end support is provided through a source plugin for each radio family — RTL-SDR, Airspy, HackRF, and others — that hands raw samples to the core. The rest of SDR#’s reach comes from its plugin API: third-party add-ons implement digital-mode decoders, frequency scanners, noise reduction, frequency-manager databases, and more, docking into the main window. This plugin model let a single receiver front end become a platform for many niche tools without those tools reimplementing the tuning, FFT, and audio plumbing.
The application is closed-source but free to download, and it has long been the flagship software for Airspy hardware, tuned to get the best out of those receivers.
Relevance to SDR
For general-purpose listening — broadcast FM, air band, ham bands, utility signals — SDR# is one of the most-used receivers in the hobby, especially on Windows where alternatives like SDRangel and Gqrx (the latter more common on Linux) compete. Its accessibility made it a standard on-ramp: plug in a dongle, run the Zadig driver installer, open SDR#, and see signals within minutes. Plugins extend it toward digital decoding, but SDR# itself is fundamentally an analog-mode receiver and spectrum browser rather than a trunking decoder.
GopherTrunk is unrelated software and shares no code with SDR#. GopherTrunk is a headless, cross-platform, pure-Go trunking scanner that ingests IQ directly and decodes digital voice/control protocols (P25, DMR, NXDN, TETRA, and more) on its own; SDR# is a Windows GUI receiver aimed at manual tuning and listening. They can, however, use the same hardware — an RTL-SDR or Airspy that works in SDR# is the same class of front end GopherTrunk consumes. Someone might use SDR# to eyeball a control channel’s frequency on the waterfall, then point GopherTrunk at that frequency to actually follow the trunked system.
Sources
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SDR# and Airspy downloads — the official distribution page from the Airspy team, and the Wikipedia article on SDR Sharp, covering the application, its plugin ecosystem, and supported hardware. ↩