libhackrfk

Kotlin driver for the HackRF SDR (HackRF One, Jawbreaker, rad1o), speaking the libhackrf USB host protocol over the Android USB host API. Pure Kotlin — no NDK, no native libraries, no root. Built for Android but the wire codec is Android-free and JVM-testable.

Maintained by Isak — PU3IAR. Brought to you by id.qsl.br, a platform with tools for amateur radio operators. YouTube: @qraisak

Features

• HackRfProtocol — the libhackrf wire codec, free of any Android dependency and unit-tested on the JVM:
  • Vendor request ids and payload encodings: frequency (MHz+Hz little-endian split), fractional sample rate (2–20 Msps) with the matching MAX2837 baseband filter selection, transceiver modes.
  • Gain rules exactly as the reference: LNA 0–40 dB in 8 dB steps, VGA 0–62 dB in 2 dB steps, TXVGA 0–47 dB, drive-scale mapping.
  • Signed 8-bit IQ sample conversion and the sweep block format (0x7F7F marker + u64 LE tuned frequency).
• HackRfClient — USB transport and streaming lifecycle:
  • Device identity (VID 0x1d50), permission handling, RX streaming from the bulk-IN endpoint delivered as FloatArray (i0,q0,… in [-1,1]) with an optional power spectrum, through the same callback contract as the other iSDR clients.
  • Half-duplex TX: direct RX↔TX mode switches (never through OFF, which would drop the bias tee and RF amp), front-end state re-asserted across switches, and the transmit queue streamed to the bulk-OUT endpoint.
  • Firmware-driven sweep for wideband spectrum scans, with block reassembly and marker resynchronization.
  • setFrequency / setSampleRate / setLnaGain / setVgaGain / setAmpEnable / setAntennaPower, and TX: setTxVgaGain / setPtt / submitTxIq; sweep: startSweep / stopSweep.
• TxInterpolator — polyphase Blackman-sinc interpolation raising the 48 kS/s modulator IQ to the board rate with unit DC gain per branch.

Testing without hardware

The wire codec and the interpolator are pinned by JVM contract tests in the parent project (isdr: HackRfProtocolTest, TxInterpolatorTest) — byte-exact payloads, filter and gain rules, sweep block parsing, and the measured spectral contract of the TX interpolation, all validated against the reference sources.

Credits and references

Faithful port of the reference host library and firmware semantics:

• HackRF / libhackrf — Great Scott Gadgets and contributors: https://github.com/greatscottgadgets/hackrf
• libhackrf is BSD 3-clause; its copyright notice is retained in the file headers and in COPYING.md.

Request semantics, mode-switch behaviour and streaming alignment follow the hackrf_usb firmware sources and the libhackrf host library.

License

Dual-licensed — GPLv2+ only as part of the iSDR Drivers application; all other rights reserved. See LICENSE. The upstream libhackrf BSD 3-clause notice is retained there and in COPYING.md. Kotlin port © 2026 Isak Ruas isakruas@gmail.com.