rf-agent

SDR agent for live RF spectrum streaming. Reads IQ samples from an SDR device (or a file/simulator), runs FFT, and streams spectrum frames over WebSocket to an rf-platform server.

Quick Start

pip install "rf-agent[sdr]"
rf-agent setup            # platform-specific OS prep (udev/libusb/Zadig)
rf-agent doctor           # verify everything is wired up
rf-agent connect --source rtl-sdr --freq 100000000 \
                 --server ws://your-server/ws/agent --token <token>

rf-agent setup auto-detects your platform and does the parts pip install can't do. rf-agent doctor runs read-only checks and tells you exactly what's wrong if connect doesn't work. See rf-agent connect --help for all flags.

Per-platform notes

The [sdr] extra installs pyrtlsdrlib, which bundles librtlsdr binaries for Linux/Windows/macOS. The only system dependency you still need is libusb, plus a way for non-root user-space to access the USB device. rf-agent setup handles both.

Linux (Debian / Ubuntu / Fedora / Arch / openSUSE)

pip install "rf-agent[sdr]"
rf-agent setup linux      # prompts sudo to install libusb + udev rules
# log out + back in (or `newgrp plugdev`) so plugdev membership takes effect
rf-agent doctor

What setup linux actually does (idempotent):

1. Installs libusb-1.0-0 (or the equivalent for dnf/pacman/zypper) if missing.
2. Writes /etc/udev/rules.d/20-rtl-sdr.rules with MODE="0666", GROUP="plugdev".
3. Reloads udevadm rules.
4. Adds the current user to plugdev.

Windows (native, no WSL)

pip install "rf-agent[sdr]"
rf-agent setup windows    # downloads & launches Zadig
# in Zadig: Options → List All Devices, pick 'Bulk-In, Interface (Interface 0)',
# select WinUSB, click Install Driver.
rf-agent doctor

The Zadig step is a Windows-GUI driver replacement — there's no fully automated path because Windows requires user consent for driver swaps. After setup windows opens Zadig, follow the on-screen instructions printed to the console.

macOS

pip install "rf-agent[sdr]"
rf-agent setup macos      # brew install libusb
rf-agent doctor

WSL (Ubuntu under Windows)

# (one-time, from an ELEVATED Windows PowerShell)
usbipd bind --busid <BUSID-of-your-dongle>

# inside WSL:
pip install "rf-agent[sdr]"
rf-agent setup linux       # udev rules + libusb, same as Linux
rf-agent setup wsl-attach  # attaches the dongle via usbipd; rerun after every unplug
rf-agent doctor

What pip install fundamentally cannot do

These steps require admin/root and live outside the Python packaging system. rf-agent setup automates them where it can, but the underlying constraint is real:

• Linux: writing /etc/udev/rules.d/*.rules and usermod -aG plugdev need root.
• Windows: replacing the Realtek driver with WinUSB needs admin consent (GUI).
• WSL: usbipd bind is a one-time elevated PowerShell command on the Windows host.
• macOS: brew install libusb if not already present.

Troubleshooting

rf-agent doctor says everything is OK but connect shows only noise

That's an RF problem, not a software problem. Try:

• Increase gain: --rtlsdr-gain 49.6.
• Tune slightly off-center to dodge the DC/LO spike: e.g. --freq 99500000 instead of 100000000.
• Use a longer antenna for FM (each element ~75 cm).
• Confirm a known-strong local station is within ±1 MHz of your --freq.

usb_claim_interface error -6 / "Resource busy"

Another process holds the dongle — usually gqrx, a previous rf-agent run, or the kernel's DVB driver auto-binding on hotplug. Quick recovery:

sudo rmmod dvb_usb_rtl28xxu rtl2832 rtl2830 2>/dev/null  # Linux
pkill -f gqrx ; pkill -f rtl_tcp
# or just: unplug + replug

On WSL, after a replug you also need to re-attach: rf-agent setup wsl-attach.

How it works (appendix)

librtlsdr symbol-stub workaround

pyrtlsdr 0.4.0 resolves several optional librtlsdr symbols at import time without try/except: rtlsdr_set_dithering and the GPIO helpers (rtlsdr_set_gpio_input/output/bit/byte/status, rtlsdr_get_gpio_bit/byte). The system librtlsdr shipped by Debian/Ubuntu (2.0.2) doesn't export them — and neither do the upstream osmocom or rtl-sdr-blog source trees — so import rtlsdr raises AttributeError on a stock Linux install.

When pyrtlsdrlib is present (which it is via the [sdr] extra), pyrtlsdr loads from the bundled binary which does export all 8 symbols, so this never trips.

As defence-in-depth (users on systems with a partial librtlsdr but no pyrtlsdrlib), agent/source/rtl_sdr_source.py::_install_missing_symbol_stubs monkey-patches ctypes.CDLL.__getattr__ to return no-op stubs for the missing symbols. It runs once on the first RTLSDRSource.start() call. The agent never calls these functions (GPIO + dithering control we don't need), so the stubs are inert.

USB throttling and backpressure

RTLSDRSource sleeps 1/fps between reads. The hardware buffer overruns — that's expected, we just keep the latest snapshot. Default --fps 10 means ~10 FFT frames/sec when --rtlsdr-chunk-samples is left at its default (equal to --fft-size, i.e. one chunk = one frame).

--fps is currently capped at 10 on the free tier. Premium-tier accounts may exceed this in the future; the cap is enforced at the CLI entry point (agent/cli.py::MAX_FPS_FREE_TIER).

The source emits to its output queue with latest-frame-wins semantics: if the consumer can't keep up and the queue is full, the oldest pending frame is dropped before the new one is enqueued. This prevents memory growth under slow consumers and ensures the hardware loop never blocks. Drops are visible via RTLSDRSource.frames_dropped.