compareeHub

PICTOR OPEN-SOURCE RADIO TELESCOPE DETECTS THE 21CM HYDROGEN LINE OF THE MILKY WAY

An open-source 1.5-metre radio telescope that sees the Milky Way's hydrogen glow at 1420 MHz, and you can use it online for free or study its design to build your own.

by Apostolos Spanakis-Misirlis (0xCoto)

FULL CAD BOM FIRMWARE DOCS

ScienceOpen-hardware

difficulty
●●●●○
time
a weekend-plus
license
GPL-3.0
repo
repo STABLE (NO COMMITS SINCE JULY 2023)281 stars

WHAT YOU’LL NEED

1
Jump to section

COMPAREE VERDICT

PICTOR is a 1.5-metre prime-focus radio telescope in Athens, Greece that anyone can use for free through its website, and its repository is open. It holds the GNU Radio acquisition flowgraphs, the observation and scheduling scripts, and the telescope's hardware specs, block diagram and feedhorn dimensions. It is not a step-by-step build guide: treat it as a well-documented reference design, and expect to source and point your own dish, feed, LNA and SDR. The hardest part is not the software but getting a clean signal near 1420 MHz, because local radio interference is hard to escape.

GOOD TO KNOW

  • —PICTOR is a GPL-3.0 open-source radio telescope project (software and hardware), though not a step-by-step build guide.
  • —There is no bill of materials: you source your own dish or antenna, feed, LNA and SDR, using PICTOR's published specs as a reference.
  • —The repository includes GNU Radio flowgraphs, observation and scheduling scripts, and plotting tools.
  • —The README documents the telescope and each file, but has no installation guide — you need to know GNU Radio.
  • —Hardware is documented as specs, a block diagram, feedhorn dimensions and an STL, not a step-by-step build guide.
  • —Licence allows commercial use.

Parts to buy

5 items

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

  • Software-defined radio (RTL-SDR or better)Find
  • Low-noise amplifier for 1420 MHzFind
  • Satellite dish or hydrogen-line hornFind
  • Coax and connectorsFind
  • Linux machine for processingFind

BUILDS OF THE WEEK

Five open-source builds worth your weekend, every week.

Checked like this one: what’s really in the repo, what it costs, how hard it is. One email, unsubscribe anytime.

Can I build this?

PrintNothing required. The repository's Waveguide.stl is a visualization of the feedhorn, not a print-ready part.
Buysoftware-defined radio (RTL-SDR or better), low-noise amplifier for 1420 MHz, satellite dish or hydrogen-line horn, coax and connectors, Linux machine for processing
ToolsGNU Radio installed, Python 3 environment, basic RF test equipment helpful but not mandatory, ability to aim a dish or mount a horn outdoors
Skillsintermediate Python and command-line work, basic radio astronomy concepts (Doppler shifts, drift scans, RFI), patience with signal processing — not a first SDR project
Timea weekend to get PICTOR running and integrate it with your hardware, then evenings of observation and tuning before you see a clean hydrogen line
Cost$$ — the software is free; the cost is your SDR, LNA, filter, feed and dish (the project does not publish prices).
SafetyNone beyond ordinary electronics care and safe outdoor mounting of the dish — it is receive-only and never transmits.

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

More builds like this

All projects
You can 3D print the rig that keeps a slice of living brain aliveScienceOhmPi: an open-hardware resistivity meter that images what is under the groundScienceA 200 dollar open-source gamma spectrometer that identifies which isotope is in front of itScience

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 PICTOR README (Documents the telescope hardware and describes each file; there is no installation guide.)
  2. 2.Choose your antenna: an adapted dish with a feed modelled on PICTOR's documented feedhorn, or a smaller hand-built antenna such as the separate HLine3D Yagi project (HLine3D is an independent beginner project with detailed antenna build instructions; it is not part of PICTOR.)
  3. 3.Install GNU Radio and test your SDR at 1420 MHz with a dummy load(Verify you can see the noise floor before you add an antenna.)
  4. 4.Run a test observation and plot it, using observe.py and the virgo library as a reference(Check your local interference with a few short drift scans first.)

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

  • Skipping the LNA: PICTOR puts a two-stage low-noise amplifier (noise figure under 0.5 dB) right at the feed, and a bare SDR on a long cable will struggle to see the faint 21 cm line.
  • Urban RFI will drown the hydrogen line unless you have a very quiet site or excellent filtering — the 21 cm emission is faint and the software cannot fix a bad signal.
  • PICTOR assumes you bring your own hardware and know how to point it — there is no step-by-step dish assembly guide in this repository.
  • Expecting instant results: a clean Milky Way hydrogen profile usually takes repeated observations and calibration, not one quick recording.
  • Underestimating the learning curve for GNU Radio and radio astronomy data reduction — this is not a plug-and-play SDR app.
  • Not planning for Doppler shifts: the hydrogen line from different parts of the Milky Way is shifted by the gas's motion and by Earth's own motion, so learn what a velocity correction is before you interpret your spectra.

Do I need a large dish to detect the hydrogen line?

Not necessarily. PICTOR itself is a 1.5-metre dish, but smaller hydrogen-line antennas exist: the separate HLine3D project, for example, documents a student Yagi antenna you can build with hand tools. A larger dish gives better signal-to-noise and a narrower beam, and a quiet site matters as much as aperture.

Is this receive-only, or do I need a radio licence?

Receive-only: the telescope only listens, it never transmits. Receive-only setups generally do not need a radio licence, but check your local rules.

Can I use PICTOR with a different SDR, or is it RTL-SDR only?

The flowgraphs use an RTL-SDR-style source block. In GNU Radio you can usually swap the source block for your own SDR, but the project does not document or test other radios.

What is the actual PICTOR telescope, and can I build a copy of it?

PICTOR is a 1.5-metre prime-focus dish in Athens, Greece that anyone can use for free via its web platform. The repository documents its hardware — specs, block diagram, feedhorn dimensions, LNA and filter specs — plus the acquisition software, so you can build a similar system around your own dish; it is a reference design, not a step-by-step guide.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

Around 280 stars, a 1.5-metre dish you can also use remotely through the PICTOR website, and full feedhorn dimensions in the README. Would you build your own dish and feed, or start by observing with PICTOR online first?

CompareeTEAM2mo agoedited

Practical notes from our verification: PICTOR describes itself as a fully open source software and hardware project. The README documents the telescope itself — a 1.5-metre prime-focus dish (F/D 0.411) observing 1300 to 1700 MHz, a two-stage LNA, feedhorn dimensions and measured S-parameters — and the repository includes a Waveguide.stl visualization of the feedhorn, so you get real design data, not just code. The software side is the observation pipeline: GNU Radio flowgraphs (pfb.grc, fft_integration.grc) and observe.py, which in its current form records and plots observations with the author's virgo Python library. Note that the README's file table still lists plot.py and plot_hi.py, which have since been removed. The repository was last pushed in July 2023, so treat it as a stable reference rather than an actively changing project. The single biggest challenge is not the software — it is getting a clean signal near 1420 MHz in the first place, because local radio interference at that frequency is hard to escape.

Apostolos Spanakis-Misirlis (0xCoto)

Apostolos Spanakis-Misirlis built PICTOR, with engineering help from Vasilis Spanakis-Misirlis, as a free-to-use radio telescope in Athens to promote radio astronomy education, and open-sourced its software and hardware documentation.

GitHub

Star the project on GitHub

DISCLAIMER

  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • 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.
GitHub repo