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YOU CAN BUILD A RADIO TELESCOPE THAT HEARS THE HYDROGEN OF THE MILKY WAY, FOR A FEW HUNDRED DOLLARS

A horn telescope built from insulation-board panels and a metal can hears the hydrogen line of the Milky Way, for a few hundred dollars.

by DSPIRA program, WVU Radio Astronomy Instrumentation Lab and Green Bank Observatory

FULL CAD BOM FIRMWARE DOCS

ScienceOpen-hardware

difficulty
●●●●○
time
several weekends
license
MIT
repo
repo ACTIVE0 stars

WHAT YOU’LL NEED

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COMPAREE VERDICT

DSPIRA is an NSF-funded teacher program run by West Virginia University and Green Bank Observatory. Teachers build a horn radio telescope, then take the design back to their classrooms. The horn panels and a metal paint-thinner can with a soldered feedthrough antenna form the antenna, a hand-soldered low-noise amplifier (about 30 dollars in parts; gerbers and Altium files on GitHub, no licence file) feeds an Airspy R2 software-defined radio (169 dollars), and GNU Radio on a Linux laptop does the processing. It receives the 21 cm hydrogen line at 1420 MHz; pointing along the galactic plane and measuring the Doppler shift lets you plot the rotation curve of the Milky Way, one of the classic pieces of evidence for dark matter. In the program's own words, a complete system can be built for a few hundred dollars, depending on options and whether you have a computer. The thing most likely to go wrong is the handoff between guides: the material is organised for teachers running a program, not a single builder working alone, so you stitch together the horn PDF, the LNA instructions, the SDR page and the Ubuntu and GNU Radio install yourself. If you have soldered small surface-mount parts before, the pieces are all there.

GOOD TO KNOW

  • —Horn and stand construction PDF, parts and purchase links, LNA soldering guide and software install lessons are published (lessons repo MIT).
  • —LNA gerbers and Altium files are on GitHub (no licence file); the parts list and step-by-step soldering guide with videos are on the DSPIRA lessons site. Parts about 30 dollars.
  • —Software is GNU Radio with gr-radio_astro flowgraphs (GPL-3.0).
  • —The Airspy R2 SDR (169 dollars) is not open hardware but is the documented receiver.
  • —The lessons repo is a teacher program; it is thorough but written for classroom deployment, not a standalone weekend build.
  • —No single page walks you through the entire system end-to-end; you will cross-reference the horn guide, LNA repo, equipment list and software install separately.

Parts to buy

7 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • Horn panel materialFind
  • Metal paint-thinner canFind
  • SMA feedthrough antennaFind
  • Lumber for the cradle and stand (under 50 dollars)Find
  • DSPIRA LNA board and partsFind
  • Airspy R2 SDR (169 dollars) or Airspy Mini (99 dollars)Find
  • SMA coax cableFind

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Can I build this?

Printnothing required — the horn is cut and folded from foil-faced insulation board, not 3D printed
Buyhorn panel material, a metal paint-thinner can, an SMA feedthrough antenna, lumber for the cradle and stand (under 50 dollars), DSPIRA LNA board and parts (about 30 dollars; ordering details in the LNA instructions), Airspy R2 SDR (169 dollars) or Airspy Mini (99 dollars), and an SMA coax cable
Toolstemperature-controlled soldering iron and hot air gun (about 350 °C, per the LNA guide), drill, smooth-edge can opener, saw for the wooden stand, knife for the horn panels, and a computer running Ubuntu with GNU Radio
Skillsintermediate SMD soldering (the LNA uses small surface-mount parts; the guide asks for a temperature-controlled iron and hot air), ability to follow assembly PDFs and cross-reference multiple repos, comfort with command-line software installs and GNU Radio flowgraphs, basic radio concepts (frequency, amplification, Doppler shift) help but can be learned along the way
Timeseveral weekends — horn construction is a day, LNA soldering and testing is an evening, GNU Radio setup and calibration is another day, then observing runs take patience
Cost$$ — the Airspy R2 dominates at 169 dollars, LNA parts are about 30 dollars, the rest (board, can, wood, wire, coax) is under 100 dollars if you shop carefully
Safetysoldering iron heat, otherwise none beyond ordinary electronics care — this is a receive-only system with no high voltage or RF transmission

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

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Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the Horn Construction Information page (this is the master build guide for the horn itself, with PDFs of the fold pattern and assembly photos)
  2. 2.Review the parts and purchase links on the Horn Construction Information page(The Horn Construction Information page lists the parts with purchase links: LNA options, stand lumber (under 50 dollars), Airspy SDR and the coax cable.)
  3. 3.Clone the LNA hardware repo (gerbers and schematic for the DSPIRA LNA; the parts list and soldering guide are on the DSPIRA lessons site)
  4. 4.Install GNU Radio and gr-radio_astro (the software side — flowgraphs for the Airspy and hydrogen-line observation (GPL-3.0))

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • The repo is organised for teachers running a program, not a single builder working alone — expect to cross-reference the horn guide, LNA repo, equipment list and software install separately.
  • The software is coded for the Airspy R2 (10 MHz bandwidth). The cheaper Airspy Mini (6 MHz) needs a small change to the source block; RTL-SDR, LimeSDR and ADALM-PLUTO are also documented on the Spectrometer Source Block Settings page.
  • Use the panel material specified in the horn construction PDF: the inner surface of the horn has to be conductive to guide the radio waves into the can, so do not substitute plain foam board.
  • The feedthrough antenna position in the can matters: the guide specifies a 1/4-inch hole 5.25 cm from the edge, so follow the dimensions rather than improvising.
  • The software setup assumes Ubuntu Linux. On a Windows PC the program has you partition the drive and install Ubuntu, or boot their prepared Ubuntu image from a flash drive.
  • Expect to learn what is real in the spectrum: the Airspy adds its own spike at 1420.0 MHz, and the DSPIRA docs warn about internal interference from SDRs, so shield the electronics and use the calibration lessons before you trust a hydrogen profile.

How sensitive is a horn compared to a dish?

A horn is far less sensitive than a dish of the same aperture. This one works because the 21 cm hydrogen line is bright and fills the sky along the galactic plane. You will not detect faint point sources or distant galaxies with it, but the Milky Way hydrogen is loud enough.

Can I use a different SDR instead of the Airspy R2?

The program prefers the Airspy R2, but also documents the Airspy Mini, RTL-SDR, LimeSDR and ADALM-PLUTO. Each needs a small change to the source block in the GNU Radio flowgraph; the Spectrometer Source Block Settings page explains how.

Do I need a radio license to operate this?

No — this is a receive-only system. You are not transmitting, so no license is required in any jurisdiction.

What does the rotation curve observation actually show?

You point the horn along the galactic plane and measure the Doppler shift of the hydrogen at different angles. Stars and gas farther from the galactic centre should rotate slower (like planets around the Sun), but they do not — the rotation curve is flat, which is evidence that dark matter is holding the galaxy together.

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Discussion1

FROM THE COMPAREE TEAM

The horn is far smaller than a dish, but it makes a real hydrogen-line observation of our own galaxy. What would you point yours at first — the galactic centre, or a sweep along the plane to map the rotation curve?

CompareeTEAM14d agoedited

Practical notes from our verification: the repo is a lesson site, so the build guide is split across multiple pages (horn construction, equipment list, LNA assembly, software install) rather than one walkthrough. The LNA hardware lives in a separate repo (github.com/WVURAIL/os_radio_astro_hw) with Altium files, a PDF schematic and v3 Gerbers but no licence file, so ask before redistributing it. There is video help: the horn introduction post links a video, the detailed LNA construction instructions have a video for each component, and assembling the can has three more. The LNA build involves small surface-mount parts, and the instructions recommend a temperature-controlled soldering iron and a hot air gun. The Airspy R2 is the preferred radio, with Airspy Mini, RTL-SDR, Lime and ADALM-PLUTO listed as alternatives. The lesson repo is still being updated and teachers are still building these. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

DSPIRA program, WVU Radio Astronomy Instrumentation Lab and Green Bank Observatory

DSPIRA (Digital Signal Processing in Radio Astronomy) is an NSF-funded program to bring radio astronomy into high-school classrooms. Teachers attend a summer workshop at Green Bank, build a horn telescope, then replicate the build with their students. The open-hardware LNA and lesson plans came out of the program.

GitHub Web

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  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
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