Tutorial Record IQ then the Signal workbench

Keep a signal, then take it apart without a radio.

Record

1. Start any mode with a real radio (or the synthetic source).
2. Press Record IQ in the Source panel (or run onair-cli --record auto --secs 10). With SigMF ticked each recording also gets a .sigmf-meta file.
3. Show recording opens the folder (the recordings folder of OnAir's data folder, see Settings and files).

Open it later

Choose the IQ recording file source and pick the file. SigMF (.sigmf-meta / .sigmf-data) and two-channel WAV files give the rate, centre frequency and sample format themselves; raw files (.cs8, .cu8, .cf32, .ci16, .cu16) need the rate (a name like capture_2Msps.cs8 gives it). The file then plays in any mode. onair-cli --file x.sigmf-meta does the same.

The Signal workbench

Choose Signal workbench (group General and tools).

1. Open a file with Open... or drop it on the window. Audio files (WAV, MP3, FLAC, OGG, M4A) are treated as a real signal; a stereo file can be read as I/Q ("stereo is I/Q": left = I, right = Q). IQ files open from disk as they are, so 100 MB and larger files open at once. "Demo signal" makes a recording to try the tools on.
2. Look. An overview, the waveform and a large spectrogram. Mouse wheel zooms time, Ctrl + wheel zooms frequency, right-drag pans, a click puts the cursor, a drag selects a time range and a band (Shift + drag: time only), double click clears.
3. Measure. Press Measure selection: the strongest peaks, bandwidth at -3 dB, at -20 dB and the 99 % occupied band, carrier offset, SNR, a symbol-rate estimate, a modulation guess with candidates, power over time and bursts.
4. Demodulate. Choose the demodulator (AM, FM, SSB, CW, ASK / OOK, 2-FSK / 4-FSK, AFSK, BPSK / QPSK / 8PSK, MSK / GMSK) and, for digital ones, the baud rate (Auto-detect finds it from the selection). The result shows the instantaneous frequency, phase and magnitude, the eye diagram, the constellation or soft-symbol histogram and the recovered bits. Listen plays the audio.
5. Read the bits. The Bits tab applies invert, differential decode, NRZI, Manchester, byte reversal and byte alignment, shows the stream as hex, binary or ASCII, and searches a pattern (also inverted, with some wrong bits allowed).
6. Export. The Export tab saves the selection as .wav, .cf32 or SigMF, the demodulated audio as .wav, the bits as .txt or .bin and the peak table as CSV.

wbtool (built with the tests) does the same on the command line: wbtool gen out.cf32 --kind qpsk --rate 250000 --baud 12500 makes a test recording with known bits, wbtool analyze file --rate R, wbtool demod file --kind fsk2 --baud 9600 --band f0 f1.

Related: Signal workbench, Use the sample library, IQEngine.