Also known as: Gqrx
Gqrx is a free, open-source software-defined radio receiver application that pairs a GNU Radio signal-processing back end with a Qt graphical interface.1 It is one of the most popular general-purpose SDR receivers on Linux and macOS, offering a spectrum and waterfall display, a set of analog demodulators, and recording and remote-control features. Gqrx fills much the same role on those platforms that SDR# does on Windows.
How it works
Under the hood, Gqrx constructs a GNU Radio flowgraph: a hardware
source (via gr-osmosdr or SoapySDR) feeds a
digital down-converter that shifts and decimates the
tuned slice of spectrum, followed by mode-specific demodulators and an audio sink. The Qt
layer draws the FFT-based spectrum and waterfall and exposes
the controls — center frequency, gain, filter width, squelch, and the demodulator choice
(WFM stereo, NFM, AM, SSB, CW).
Because the DSP is standard GNU Radio, Gqrx inherits broad hardware support: RTL-SDR,
Airspy, HackRF, bladeRF,
USRP, and anything with a SoapySDR module. Useful conveniences
include baseband and audio IQ recording, an AGC, a noise blanker, and a
remote-control TCP interface (compatible with the rigctld protocol) so other software or
scripts can retune Gqrx and read its state. That remote interface makes Gqrx scriptable — for
example, an external program can command it to step across a band.
Relevance to SDR
Gqrx is a staple general-coverage receiver for the Linux and macOS SDR community: it is the tool many reach for to tune broadcast, air band, marine, ham, and utility signals, and to confirm a new dongle is working. Being open source and GNU Radio-based, it is also a common starting point for people who later dig into the underlying flowgraph. Like most such receivers, its built-in demodulators cover analog modes; digital-voice and trunking work is left to dedicated decoders, though Gqrx’s audio or IQ output can be piped into one.
GopherTrunk is independent of Gqrx and shares no code with it. GopherTrunk is a headless, pure-Go trunking decoder with its own DSP; Gqrx is a GUI receiver built on GNU Radio. The overlap is at the hardware and the “look at the spectrum” stage: an operator can use Gqrx to find and inspect a control-channel carrier on the waterfall, then hand that frequency to GopherTrunk to follow the system. Gqrx’s IQ recordings can also serve as capture files for offline testing of a decoder.