Radio Astronomy With An Old TV Satellite Dish
A great project for amateur astronomers, ham radio operators, and SW enthusiasts
Something I have been thinking about for a long time is amateur radio astronomy. There are an abundance of old C-Band and Ku-Band dishes that people would be delighted if you simply haul them away, and they can be converted into receivers for the 21cm band, and potentially other bands. Add a second dish and you can create an interferometer, GREATLY increasing the resolution. Here’s a primer…
Hydrogen Line (21 cm / 1420 MHz) Observations – Your Starting Point
This is the classic amateur radio astronomy target: the spectral line from neutral hydrogen in the Milky Way.
You can detect Doppler-shifted signals to map galactic arms, measure rotation, or even see the shape/structure of our galaxy.
Strong sources like the galactic plane or Cygnus A are detectable.
Many people use drift scans (point the dish fixed at zenith and let Earth rotation sweep the sky) — no motors needed at first.
Modifications needed: Remove the original LNB and install a custom feedhorn (simple aluminum tube + probe or cylindrical choke, ~$50–100 kits available) plus a low-noise amplifier (LNA) tuned to 1420 MHz. Feed into a cheap RTL-SDR dongle (~$30) or better SDR. Software like SDR# or Radio-SkyPipe works great for recording spectra.
Here’s what a typical hydrogen-line spectrum from a DIY dish setup looks like (peak around 1420.4058 MHz with velocity shifts showing galactic motion):
2. Solar Radio Observations (Very Easy & Rewarding)
The Sun is the strongest radio source in the sky and produces bursts during flares/coronal mass ejections.
You can monitor daily solar activity, detect flares in real time, and even create simple radio “images” or light curves.
Works at 1420 MHz or keep the original Ku-band LNB for ~11–12 GHz continuum.
Perfect for daily tracking — solar radio storms affect Earth’s tech too, so it’s citizen-science gold.
3. Jupiter’s Radio Emissions
Jupiter emits strong radio signals from its magnetic field and interactions with Io (especially decimetric emission around 0.5–3 GHz).
You can “listen” to its bursts and monitor how they vary with rotation.
Not as strong as the Sun, but detectable with a 2 m dish + good LNA.
4. Other Continuum Sources & Sky Mapping
Bright radio objects like Cassiopeia A (supernova remnant), Cygnus A (radio galaxy), or the galactic center.
With motorized tracking you can scan small patches of sky and build crude radio maps (e.g., geostationary satellites appear as steady “radio stars”).
Star clusters themselves are weak radio emitters, but you can point at interesting regions (e.g., star-forming areas or supernova remnants) using their coordinates. The dish won’t resolve individual optical stars, but it’s great for large-scale galactic features.
Tracking the Sky (Stars, Sun, Jupiter, etc.)
Old satellite dishes usually have azimuth-elevation mounts that are easy to motorize.
Add cheap pan/tilt mechanisms (repurposed security camera PTZ heads or stepper motors + Arduino/Raspberry Pi).
Control via open-source software (e.g., the Mini Radio Telescope/MRT project on GitHub uses a DirecTV dish + RTL-SDR + automatic rotor for full tracking and sky mapping).
You can slew to specific RA/Dec or track sidereally like an optical telescope. Many builds track the Sun or Jupiter continuously.
Examples of motorized DIY satellite-dish radio telescopes:
Low-Cost Interferometer with a Second Dish (100 m Away)
This is the exciting advanced step! A 100 m east-west baseline gives ~30–40× better resolution than a single dish at 1420 MHz (fringe spacing ~7 arcmin).
You can measure source sizes/structures, resolve finer details in the Sun or galactic hydrogen, or see interference “fringes” as sources cross the beam.
Examples exist: SARA members have built working two-dish H-line interferometers with old TVRO dishes (even short 4 m baselines produce fringes).
How to do it low-cost:
Two identical dishes + feeds/LNAs + SDRs per dish.
Simplest: RF combiner for an “adding” interferometer (fringes on strong sources like the Sun).
For 100 m: run coax (or downconvert first), use separate receivers, record IQ data, and correlate offline in software (GNURadio, Python, or free tools). GPS timing helps for phase stability.
Challenges: cable loss/phase drift over 100 m, RF interference, and synchronization (not trivial, but amateurs have done it). Start with dishes closer together to test.
Real two-dish amateur interferometer builds:
Practical Tips to Get Started
Location: Away from Wi-Fi, cell towers, and power lines (RFI kills weak signals).
Software: SDR#, Radio-SkyPipe, or open-source H-line tools. Raspberry Pi for automation.
Cost: Dish free/cheap; feed + LNA + SDR ~$100–200; motors ~$50–150.
Communities: Society of Amateur Radio Astronomers (SARA), RTL-SDR forums, r/radioastronomy. Projects like PICTOR or MRT have full open-source plans.
This setup won’t rival professional telescopes, but you’ll genuinely “listen” to the cosmos — galactic hydrogen, solar storms, Jupiter’s magnetosphere, and more — right from your property. Start with a single-dish H-line drift scan (easiest win), add tracking, then consider the interferometer once you have one dish working. It’s a fantastic, hands-on project that many amateurs have succeeded with.
This article was written with the assistance of Grok AI.
More Resources:
https://www.ccera.ca/papers/a-21cm-radio-telescope-for-the-cost-conscious/
https://hackaday.com/2019/10/22/a-miniature-radio-telescope-in-every-backyard/
https://groups.google.com/g/sara-list/c/IC5sHGIZ6Io
Great DIY project idea! When I belonged to a local astronomy club, I remember one of the guys built a similar radio telescope with an old dish, plus another receiver that looked like it had been cobbled together with stuff laying around the garage. With the latter, you'd never think it could do anything by looking at it, but the sounds it made told another story!
Not an astronomer, and much of this is way beyond my ability to comprehend, but I wanted to tell you that your article is most impressive. It shows a depth of knowledge few might comprehend, so I tip my hat to your endeavors.
Thanks for sharing this .