RASTA is an experimental .NET 10 WPF MVVM application for amateur radio astronomy. It is a personal, exploratory project building a real working hydrogen‑line (1420 MHz / 21cm) observation workflow — telescope control, SDR capture, and spectral reduction — around a DIY 1.4m dish, an ASCOM Alpaca-driven mount, and an RTL-SDR receiver.
There is no guarantee this project will ever be "finished" — and that's part of the fun. RASTA is a space to learn, experiment, and gradually assemble a system that produces meaningful 1420 MHz data.
RASTA exists because radio astronomy is fascinating — and because building your own tools to explore the universe is even more fascinating.
Long‑term aspiration:
A unified, hobby‑grade radio astronomy application that can plan observations, control a telescope, capture SDR data, reduce hydrogen‑line spectra, and visualise results — all in one place.
Whether it reaches that goal or not, RASTA is designed to be a rewarding engineering journey.
- A working hydrogen‑line reduction pipeline (
HiStreamingAccumulator/HiStreamingPipeline): frame accumulation → DC/LO-spike excision → bandpass flattening (capture ÷ baseline) → RFI-rejected linear continuum fit → continuum subtraction → optional Savitzky–Golay or moving-average smoothing → velocity axis with an analytic LSR Doppler correction. An opt-in narrowband-RFI despike pass (robust, MAD-based detection with hysteresis growth) can excise things like a USB3/mount-controller comb spur from a spectrum before it's used. A separate fixed-256-bin port of the SKAO TTRT reference pipeline is kept alongside it for cross-checking. - Telescope control via ASCOM Alpaca — connect/disconnect, park/unpark, slew, track — with automatic recovery if the mount connection drops mid-session (any in-flight capture is cancelled, connection state is reset, and the app returns to Prepare with an explanation).
- SDR capture via RTL‑SDR, with hot-plug detection (tested with a Nooelec NESDR SMArtee V5 and RTL-SDR.COM V3).
- A real calibration routine: a gain sweep that hard-rejects any gain showing genuine ADC saturation (checked on the raw I/Q bytes, not inferred from the spectrum) and scores the survivors on flatness/spur-count/slope, followed by a baseline capture against automatically located, obstruction-checked cold-sky positions (falling back to a terminator only as an earlier, coarser step).
- Real, measured progress reporting throughout (captured bytes, chunks processed, files read, positions processed) — not a simulated animation — for calibration, sweep capture, and chart/ mosaic generation alike, each with its own Cancel button.
- A capture sweep that drives the mount through a plan (keeping tracking on for every slew, even if the plan itself doesn't ask for continuous tracking), saves raw IQ to FITS with full pointing (RA/Dec and Az/Alt) and site metadata baked into the header, shows a live, continuously-averaging HI spectrum as each dwell point is captured, and can be cancelled mid-run without leaving a partial FITS file behind. A Quick Capture mode grabs a single file at wherever the mount is currently pointed, for hand- or third-party-tool-positioned observing.
- A Visualise view with four spectrum modes (HI vs. Frequency, HI vs. Velocity, SKAO TTRT, and a
bandpass Ratio view for sanity-checking calibration before continuum subtraction), an optional dB
scale, and automatic combining of multi-file dwell points (
..._1of2.fits,..._2of2.fits, …) selected from a single file. - A Mosaic tab that points at a whole session folder (one baseline + several multi-file dwell-point captures across different pointings, or a folder of downloaded LAB Survey profiles), reduces each position through the same HI pipeline, and renders it three ways: a 2D sinusoidal-projection sky heatmap (line strength or peak velocity, nice-number axis ticks/gridlines, optional smoothed/ blended render), a from-here-right-now Zenith Dome (a naked-eye-style Alt/Az view at any chosen moment), and a 3D Dome extrusion of that same view — stems or an optional fitted mesh, clickable to select the matching row in the positions table, sharing a visible-spectrum colour ramp with the 2D heatmap throughout.
- A Plan view built around a "Radio Sky" hemisphere map — a Milky Way backdrop rendered from real HI4PI all-sky neutral-hydrogen survey data (downgraded offline to a small embedded grid, see Acknowledgments below), a plan's own capture points shown all at once or stepped through as an animation using the same ordering/ horizon-validation logic a real sweep uses (so it's genuine pre-flight validation, not just a raw grid), a toggle between the dome's usual Alt/Az reference frame and a live RA/Dec meridian/parallel grid, and a freeform "trace a region on the map" alternative to typing RA/Dec limits that auto-generates a coverage grid at a chosen angular spacing. Right-click any point to slew the mount there and hand off straight into a Quick Capture. Needs neither an SDR nor a mount to use — planning can be done fully offline — and a plan's default point spacing is suggested from the antenna's own estimated beamwidth (dish diameter, set on Prepare) rather than starting at zero.
- A Windows installer (WiX-based MSI + Burn bootstrapper) that chains in the .NET 10 Desktop Runtime automatically, plus a one-command release build script.
RASTA is not a polished product — it's a growing, working system with some still-placeholder edges (see below).
RASTA is structured around four workflow stages:
Connect to the telescope and SDR, configure site/frequency/gain/FFT parameters, and run calibration as three independent, resumable steps: load a saved calibration, run a device gain sweep, and capture a baseline against an automatically located cold-sky position (with a manual obstruction check and re-pick loop).
Create observation plans — equatorial or Az/Alt sweeps, a freeform region traced directly on a sky map, or drift scans — with configurable dwell time, files per dwell point, and settle time. A "Radio Sky" hemisphere map shows the plan's own capture points (all at once or animated) against a Milky Way backdrop rendered from real HI4PI survey data, in either an Alt/Az or RA/Dec grid, and lets you right-click a point to slew the mount there and jump straight into a capture. Works entirely offline — no SDR or mount required just to plan. Plans can be saved, loaded, and reused.
Execute the plan: slew and track, capture raw IQ per dwell point (optionally as multiple files), show a live-updating HI spectrum built against the calibration baseline as each point is captured, and write everything to FITS with real progress feedback. Both a full sweep and a single-shot Quick Capture can be cancelled in flight.
Load a baseline and/or capture FITS file (or a whole multi-file dwell point at once) and render it through one of four DSP modes, with dB scaling, optional smoothing/despiking, and an LSR velocity correction — or switch to the Mosaic tab to turn a whole session folder into a sky map.
- RASTA.Core — domain models, interfaces, telescope/SDR abstractions, astronomy math (LST, RA/Dec ↔ Az/Alt ↔ Galactic, LSR Doppler correction), and antenna beamwidth estimation
- RASTA.Infrastructure — ASCOM Alpaca telescope client, RTL‑SDR capture, FFT engine, JSON storage providers
- RASTA.Processing — the HI reduction pipeline, calibration (including cold-sky site selection), sweep planning, and the Mosaic sky-map's gridding/visualisation-data builders
- RASTA.App — the WPF MVVM application
- RASTA.Tests — placeholder project only; no tests yet, excluded from the default build
- RASTA.Simulators — placeholder project only; no simulated hardware yet, excluded from the default build
- RASTA.Setup / RASTA.Bundle — the WiX-based MSI installer and Burn bootstrapper (chains in the .NET 10 Desktop Runtime) used to build a distributable installer
- Telescope: ASCOM Alpaca compatible mounts, via the ASCOM Remote Server (not direct COM)
- SDR: RTL‑SDR (tested with a Nooelec NESDR SMArtee V5 and RTL-SDR.COM V3)
- LNA: SAWbird H1+ (used as the calibration front end)
- Antenna: DIY 1.4m dish + hydrogen‑line feed
RASTA is in active, exploratory development. The Prepare → Plan → Capture → Visualise path is a real, working loop end to end.
- The app connects/disconnects to an ASCOM telescope mount via the ASCOM Remote Server, offers to unpark a parked mount on connect (and to re-park on disconnect), and recovers gracefully if the live connection to the mount is lost mid-session.
- It responds to plugging/unplugging an RTL-SDR device. An SDR (and a connected mount) must be available to unlock Capture; Plan needs neither and can be used fully offline.
- Prepare runs calibration (gain sweep + cold-sky baseline capture) as three independent, resumable steps with their own dwell-time settings, and can reuse a previously saved calibration profile. Its Site Settings panel also takes the antenna's dish diameter and focal length, used to estimate a beamwidth and suggest a default point spacing for new plans.
- Plan builds and saves equatorial/Az-Alt sweep, freeform region, or drift-scan plans, previewed and validated on a Radio Sky hemisphere map before ever slewing for real.
- Capture runs a sweep plan, capturing raw IQ (optionally several files per dwell point) and showing a live HI spectrum as it goes, or a single Quick Capture at the mount's current position; either can be cancelled without leaving a partial file behind.
- Visualise loads baseline/capture FITS (auto-combining multi-file dwell points) and renders HI Frequency, HI Velocity, SKAO TTRT, or Bandpass Ratio charts (plus a standalone frequency/power view when only a baseline or only a capture file is selected), with dB scaling, optional smoothing/despiking, and an LSR velocity correction applied from each file's recorded pointing, time, and site; its Mosaic tab turns a whole session folder into a 2D/3D sky map.
- A release installer can be built in one step via
scripts/Build-Release.ps1.
These are hopes, not promises:
- Real-time waterfall view
- Automated multi-target calibration sequences
- Multi-night drift-scan accumulation (partial support exists in the Mosaic view's full-sky grid, which is designed to fill in across many sessions over time)
- A real automated test suite and hardware simulators (currently both stub projects)
- Plugin system for custom processing modules
RASTA builds on work generously shared by others in the amateur/educational radio astronomy community:
- SKA Observatory — the
SkaoPipelineProcessor/SKAO TTRT mode is a C# port of the reduction pipeline from the Ska Tabletop Radiotelescope project (built out of a SKAO Design Thinking Workshop), kept in RASTA specifically to cross-check the main HI pipeline's output. RASTA's own Prepare (gain sweep + cold-sky baseline calibration) / Capture (sky spectrum, HI velocity plot) workflow follows the same shape as the SKAO tabletop telescope's. Licensed BSD-3-Clause, © 2023 SKA Observatory. - Daniel M. Kamiński — an early signal-averaging
chain (median filter, RFI detector, intermediate/long-term averaging, background subtraction,
Savitzky–Golay smoothing) was adapted from his "SDR AVE" Advanced Signal Averaging Plugin for SDR#
(SDRSharp), licensed GNU AGPL-3.0. It's since been removed from RASTA — comparing it against the
original plugin showed it was designed as a live, continuously-refreshing display (a sliding
window), not a full-dwell integrator for a fixed recorded file, so it was never suited to reducing
a whole capture into one spectrum the way
HiStreamingAccumulatornow does. Its one still-useful piece, the Savitzky–Golay smoothing kernel, lives on inRASTA.Processing/Dspand is also used byHiStreamingPipeline's own optional smoothing pass. - HI4PI Collaboration — the Plan view's sky map background is a real Milky Way, not a drawing: it's sampled from the HI4PI all-sky neutral-hydrogen (HI) column-density survey (Effelsberg-Bonn HI Survey + Galactic All-Sky Survey combined), downgraded offline from the full HEALPix release to a small grid embedded in the app. Citation: HI4PI Collaboration et al., A&A 594, A116, 2016. Acknowledgement, reproduced as required by the data source: "The Parkes Radio Telescope is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. The EBHIS data are based on observations performed with the 100-m telescope of the MPIfR at Effelsberg. EBHIS was funded by the Deutsche Forschungsgemeinschaft (DFG) under the grants KE757/7-1 to 7-3." Distributed via NASA's LAMBDA archive under: "Permission is granted for publication and reproduction of this material for scientific and educational purposes."
Thank you all — RASTA wouldn't have gotten this far without having real reference implementations and real data to learn from and check against.
Because building your own radio astronomy tools is fun. Because learning is fun. Because seeing a hydrogen‑line bump in data you captured yourself is magical.
RASTA is a hobby project — a place to explore ideas without deadlines, pressure, or expectations.
GNU AGPL 3.0
This is a personal project, but contributions may be welcomed once the core stabilises.
Phil Crompton Coalville, UK Software developer & astronomy enthusiast