RXScope

Windows-native SDR receiver, spectrum analyzer, and multi-channel signal classifier.

Developed primarily for the Xiegu G90 transceiver. Rig control relies on the internal Detent engine, which implements a specific subset of transceiver commands and is not a complete drop-in replacement for OmniRig.

Platform support is strictly limited to Windows. Requests regarding Linux compatibility, support, or ports will be ignored and redirected to the depths of the freedesktop ABI.

Architecture

RXScope does not use external framework dependencies. Windowing relies directly on Win32 FFI, rendering runs on a custom Vulkan 1.1 pipeline, font handling uses a built-in TrueType parser and signed-distance/area rasterizer, and audio streaming interacts directly with WASAPI and waveIn.

The software operates in two distinct functional modes:

• Skimmer mode: Keeps incoming audio unaltered. Drives a bank of independent keying detectors across multiple carriers, decodes digital protocols, runs automatic mode classification, and logs station callsigns.
• Receiver mode: Operates as an SDR processing chain. Applies I/Q correction, software-defined tuning, filtering, demodulation (AM, SAM, FM, SSB, CW), noise blanking, spectral/predictive noise reduction, AGC with hang, and audio monitoring.

Signal Processing

The signal processing engine runs on the render thread to ensure synchronous texture updates and zero-copy data presentation.

Audio Ingestion

• Backends: WASAPI shared mode, WASAPI exclusive mode, loopback capture, and legacy waveIn.
• Channel routing: Left, Right, Mix, and Difference modes.
• Conditioning: Single-pole high-pass DC blocker (-3 dB at 20 Hz), linear gain control, and peak/RMS measurement before processing.
• Rate conversion: Windowed-sinc polyphase resampler converting arbitrary device rates (e.g. 44100 Hz, 48000 Hz, 192000 Hz) to the internal processing clock.
• Quadrature handling: Accepts direct I/Q stereo pairs with amplitude (-12 dB to +12 dB) and phase (-45 deg to +45 deg) manual balancing, or synthesizes analytic signals via a 63-tap Hilbert transform for real inputs.

Spectral Analysis and Waterfall

• Transform sizes: Radix-2 FFT from 256 to 65536 points.
• Windowing functions: Rectangular, Hann, Hamming, Blackman, Blackman-Harris, Nuttall, FlatTop, and Kaiser (with configurable beta).
• Zoom resolution: Automatically increases FFT size with zoom factor up to four times nominal width to preserve line rates.
• Texture mapping: R8 single-channel texture mapped through a 256-entry palette in the fragment shader, minimizing PCIe bandwidth and allowing dynamic palette/gamma adjustments over past history.
• Horizontal tracking: Retains frequency alignment during dial changes without copying or clearing historical pixel buffers.
• Trace overlays: Real-time trace, decayed peak-hold trace, tracker search surface, and running average power trace.

Demodulation and Decoding

Receiver Chain (SDR Mode)

• Filtering: Complex bandpass filter with independent low and high frequency cutoffs relative to the tuning point.
• Demodulators: Upper Sideband (USB), Lower Sideband (LSB), Double Sideband AM, Synchronous AM (SAM with second-order PLL carrier recovery), FM (instantaneous phase discriminator), and CW (local beat oscillator).
• Interference reduction: Pre-filter wideband impulse blanker (0.5 ms window), post-filter narrow impulse blanker (4.0 ms window), manual biquad notch, and automatic tone-tracking notch.
• Noise reduction: Selectable LMS adaptive predictor (for periodic signals/CW) or multi-band spectral subtraction (for speech).
• Output AGC: Attack, hang timer (to prevent noise pumping during pauses), release, and target level controls, followed by an adjustable hysteresis squelch.

Decoders (Skimmer Mode)

• CW: Multi-channel tracking bank (up to 16 concurrent channels). Uses Goertzel matched filters, median-filtered envelope followers, adaptive slicing thresholds, element ratio analysis, automatic speed tracking (5 to 60 WPM), and Farnsworth spacing detection.
• RTTY: Dual-tone matched discriminator, automatic baud rate estimation, automatic shift calculation, AFC, ATC (threshold correction for selective fading), and automatic polarity inversion detection. Supports Baudot (ITA2 with USOS) and 7/8-bit ASCII.
• PSK31: Differential BPSK demodulator, raised-cosine matched filter (31.25 baud), symbol timing recovery via envelope phase evaluation, and Varicode decoding.
• Signal classifier: Automatic identification of CW, RTTY, PSK31, and NAVTEX based on spectrum peak distributions and decoder confidence metrics.
• Station spotting: Offline callsign resolution via standard cty.dat prefix files and user-defined local databases, tracking frequency, SNR, WPM, and UTC timestamps.

Storage and Replay

• Cyclic recorder: Writes continuous .rxr segment files to disk with pre-allocated block budgets.
• Metadata preservation: Embeds UTC timestamps, precise dial frequencies, software tuning offsets, reception modes, and signal levels into every block header (0.05 s to 5.0 s intervals).
• Paced replay: Replays past recordings through the DSP and decoder pipelines without display stalls, supporting variable speeds (0.25x to 8.0x), looping, and live-edge tracking.
• Export pipeline: Exports selected segments to standard uncompressed WAV (16-bit PCM or 32-bit float), custom lossless compressed audio (.rxl), or Quite OK Audio (.qoa).

Rendering Subsystem

The visual interface is rendered via Vulkan 1.1 without third-party UI frameworks.

• Memory layout: Separate dynamic vertex, index, and staging buffers per in-flight frame.
• Batching: Merges draw primitives across panel boundaries based on texture handles and scissor rectangles.
• Text rendering: Custom TrueType font parser (head, hhea, maxp, hmtx, loca, glyf, cmap, kern) with analytic signed-area rasterization into a dynamic single-channel atlas.
• Window management: Custom non-client area handling for borderless styling with DPI-aware multi-monitor scaling.

Building

Building requires the Vulkan SDK and a standard Rust toolchain (MSVC recommended).

The build script compiles GLSL shaders to SPIR-V using glslc or glslangValidator and packages Windows resource icons.

# Build release binary
cargo build --release

Environment variables recognized by build.rs:

• RXSCOPE_GLSLC: Explicit path to the glslc or glslangValidator executable.
• RXSCOPE_ICON: Path to an alternative .ico file.

Configuration

Settings are stored in an INI file placed next to the binary (rxscope.ini). Missing keys are populated with defaults on startup.

[rig]
enabled = true
profile = g90-detent
port = COM5
baud = 19200
transport = direct
rf_axis = true

[receiver]
mode = skimmer
iq_input = false
detector = usb

[audio]
backend = wasapi
dsp_sample_rate = 12000
channel_mode = left

License

This software is released under the Zero-Clause BSD (0BSD) License. Refer to the LICENSE file for details.