Inspectrum is a free tool for examining signals that have already been recorded, mainly captures made with a software-defined radio. Mike Walters, known on GitHub as miek, released the first version in October 2015, and the code is licensed under the GPL v3. A decade on, the project is still moving: version 0.4.0, released in December 2025, added support for Qt 6, the current generation of the graphical toolkit behind its interface.
What Inspectrum is for
Everything starts with a file. You first record a transmission with a receiver or a capture utility, then open it in Inspectrum to study it at leisure. The program draws a spectrogram, showing how frequencies are spread over time, which you can pan and zoom freely. According to the project repository it copes with files over 100 GB, so very long captures can be examined without being cut into pieces first.
Once the signal is located, you select it and derive amplitude, frequency or phase traces, or a plot of the raw I/Q samples. Cursors placed on those traces measure a period or a symbol rate and then pull out the sequence of transmitted symbols. Results can be exported in several forms: the selected time slice, the filtered samples or the demodulated data. This is the standard radio reverse engineering workflow, the one used to work out how a remote control, a home weather station or a wireless sensor talks.
Inspectrum reads SigMF recordings plus a long list of raw formats identified by file extension, from GNU Radio’s complex floating-point files to the 16-bit integers of bladeRF boards, the signed 8-bit samples of HackRF and the unsigned 8-bit output of RTL-SDR dongles. It does not control any radio, though. That is the key difference from SigDigger, which also analyses live signals and demodulates in real time. The two often work as a team: spot a transmission with SigDigger, record it, then take it apart in Inspectrum.
Who is it for?
The tool suits curious radio amateurs, security researchers looking into wireless protocols, telecom students and anyone who wants to understand an unknown digital signal from a capture. Its single-window interface gets straight to the point, which makes it approachable for anyone already comfortable with modulation basics.
Its scope is narrow by design. Inspectrum does not record, does not play audio and does not decode any protocol end to end: it helps you measure and extract bits, and the interpretation is up to you. Internally it works with 32-bit values and truncates 64-bit samples when loading them. There is no project website, no detailed manual and no official Windows installer. For real-time demodulation or live spectrum browsing, SigDigger or Gqrx are better choices, and controlling a radio from code means going through its own driver, such as UHD for USRP hardware.
Download Inspectrum safely
The one authoritative source is the miek/inspectrum repository on GitHub. It ships no executables, only source archives for each release, and points to the usual distribution channels instead. On Linux, Inspectrum is packaged by most distributions. On macOS, the repository lists Homebrew and MacPorts. On Windows, it recommends conda-forge or radioconda, a bundle that gathers many software-defined radio tools. Building it yourself requires CMake, FFTW 3, the liquid-dsp library at version 1.3.0 or later and either Qt 5 or Qt 6.
The program is free and has no paid option. Since the author does not distribute any binaries himself, a file billed as “the official Inspectrum installer” on a third-party site must have been produced by someone else. Your system’s package manager, or conda-forge on Windows, remains the safest route.
Frequently asked questions
Can Inspectrum capture signals?
No. It only analyses files that have already been recorded. Capturing is done with other software, such as GNU Radio or the utility supplied with your radio, bladeRF-cli for instance, and the resulting file is then opened in Inspectrum.
Does Inspectrum run on Windows?
Yes, but without an official installer. The repository suggests installing it through conda-forge or radioconda, both of which provide a ready-to-use build. Compiling it manually is also possible.
Which file formats does Inspectrum accept?
SigMF recordings and many raw formats, complex or real, at 8, 16, 32 or 64 bits. Files with an unrecognised extension are read as 32-bit complex floating-point samples by default.
