rtl_power

wideband spectrum scanner for RTL-SDR USB dongles

TLDR

Scan the FM broadcast band with 125 kHz bins, 10 s per row

$ rtl_power -f [88M:108M:125k] -g [50] -i [10] [fm_band.csv]

Single sweep of the aviation band (no integration)

$ rtl_power -f [118M:137M:25k] -1 [airband.csv]

Continuously integrate with 60 s rows

$ rtl_power -f [144M:148M:10k] -i [60] [ham2m.csv]

Run for one hour then exit

$ rtl_power -f [88M:108M:125k] -e [1h] [fm.csv]

Pick a specific device (multiple dongles)

$ rtl_power -d [1] -f [400M:410M:10k] [out.csv]

Apply a PPM frequency correction

$ rtl_power -p [58] -f [400M:410M:10k] [out.csv]

rtl_power turns an RTL-SDR USB dongle into a wideband spectrum analyzer by repeatedly retuning across the requested range, taking short FFT captures per tuning, and logging averaged power per frequency bin. It is the standard tool for long-running band surveys, RFI hunting, and unattended spectrum recording.Ranges wider than the dongle's instantaneous bandwidth (~2–3 MHz usable) are stitched together by fast retuning; expect small seams where tunings meet.

PARAMETERS

-f lower:upper:bin-size

Frequency range and bin size (e.g. `88M:108M:125k`). Bin size sets FFT resolution.

-i seconds

Integration interval per row. Longer values reduce noise but increase row period. Default: 10.

-g gain

Tuner gain in dB (usable range depends on tuner). `0` selects automatic gain.

-p ppm

Frequency correction in parts-per-million.

-c crop

Crop percentage (0–1) to discard from each tuning's edges (to avoid filter roll-off).

-s sample-rate

Hardware sample rate (default 2048000).

-w window

FFT window function: `rectangle`, `hamming`, `blackman`, `blackman-harris`, `hann-poisson`, `youssef` (default).

-F n

Enable extra integration by averaging n FFT buffers (`-F 9` is typical for very wide scans).

-O

Enable offset tuning (useful with some tuners to push away DC spike).

-d index

Device index for systems with multiple dongles.

-e duration

Exit after the given time (e.g. `30s`, `15m`, `1h`, `1d`).

-1

Perform a single measurement pass and exit.

-h

Hold the currently tuned frequency (debug).

Write CSV to stdout instead of a file.

OUTPUT

Tab- or comma-separated rows of:

$ date, time, freq_low, freq_high, step, samples, dB_bin_0, dB_bin_1, ...

Pipe to heatmap.py (ships with rtl-sdr) for a waterfall image.

CAVEATS

Requires an RTL-SDR-compatible DVB-T dongle and the `rtl-sdr` tools. Wider ranges and smaller bin sizes dramatically increase CPU and scan time. Temperature drift affects PPM accuracy; calibrate with `rtl_test -p` on a known beacon.

HISTORY

rtl_power ships with the rtl-sdr tools, originally written by Kyle Keen and maintained by Osmocom. The project was born from the discovery (circa 2012) that Realtek RTL2832U DVB-T demod chips could be switched into I/Q SDR mode.