The HackRF One
The HackRF One is a highly versatile SDR — the Swiss-army knife of spectrum exploration.
| Characteristic | Value | What it means |
|---|---|---|
| Coverage | 1 MHz → 6 GHz | from AM radio to 5 GHz WiFi, a huge window |
| Sample rate | up to 20 MSps | ~20 MHz observed at once (see Échantillonnage, Nyquist et aliasing) |
| Resolution | 8 bits | modest dynamic range (~48 dB) → gain needs care |
| Duplex | half-duplex | it transmits or receives, never both — here, receive-only |
| Connector | SMA female | + external clock ports (CLKIN/CLKOUT) for synchronisation |
| Power | USB bus | a short, good-quality cable avoids many mysteries |
The gain chain: three knobs, one goal
| Stage | Range | Role | Suggested starting point |
|---|---|---|---|
| RF amp | 0 or +14 dB | input boost | off (only as a last resort) |
| LNA (IF) | 0–40 dB, steps of 8 | amplifies at the antenna side | 16–24 dB |
| VGA (baseband) | 0–62 dB, steps of 2 | adjusts before the sampler | 20–30 dB |
The method: start low, raise the LNA until your signals rise out of the noise floor, fine-tune with the VGA — and back off as soon as the whole floor rises or "ghost" peaks appear: that's saturation, and a saturated receiver invents signals that don't exist. On 8 bits, slightly too low beats slightly too high.
In this site's interface, the single slider distributes LNA/VGA for you — but knowing what it drives will help you in any other SDR software.
Known traps (and their fixes)
- The centre spike (DC spike): a peak pinned exactly at the tuning frequency, whatever you do. A direct-conversion artefact, not a signal — offset by a few hundred kHz to study a precise frequency.
- Overwhelming city FM: broadcast transmitters can saturate the whole front end even when tuned elsewhere. Lower the LNA, or add an FM band-stop filter (~$15).
- USB noise: shielded extension, away from hubs and screens; the HackRF is sensitive to its electrical surroundings.
- Static electricity: the input isn't protected against strong discharges — no outdoor antenna without protection, and touch grounded metal before the SMA connector.
Software side
- In the browser (this site): Chrome/Edge drive the HackRF over WebUSB — click "Plug in my SDR" in the console. The serial number shows once connected.
- Command line:
hackrf_infoconfirms firmware and serial number. - On a server/Pi: through SoapySDR (
driver=hackrf), the same API everywhere.
It needs an antenna matched to the target band — the bundled ANT500 is a compromise, and the tuning guide will help you get the most out of it.
Your turn
- The noise floor just jumped 15 dB across the whole window. Diagnosis? (Saturation — lower the LNA.)
- Why leave the RF amp off by default? (+14 dB before any filtering: it saturates first, especially in town.)
- What difference will you see between 8 and 20 MSps on the FM band? (An 8 vs 20 MHz window — more stations visible, but more machine load.)
👉 Confirm it responds: First contact