The Sun
The Sun is the easiest radio source to detect. An 18-inch satellite TV dish and a $38 USB radio will find it.
Build one →Chippewa Valley Astronomical Society · Radio Astronomy
Hear the universe.
The Sun, the hydrogen gas between the stars, and distant galaxies all give off radio waves. At Hobbs Observatory our members listen with two 20-foot dishes, and anyone can learn how, even by building a Sun detector from a used satellite TV dish.
Tonight over Hobbs
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Get involved
Come out to a work day
Work days are when members build, fix and improve the dishes, feeds and receivers at Hobbs Observatory. You do not need any experience; it is the best way to learn how a radio telescope really works.
- Sat24OctRA WorkdaySaturday, October 24, 2026 · 9:00 am–12:00 pm CDTHobbs Observatory, S1 County Hwy K, Fall Creek, WI 54742Come on out. We arrive between 9:00 and 9:45 am.Add to my calendar
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Learn
What is radio astronomy?
Light is only a thin slice of the electromagnetic spectrum. Radio waves are the same kind of wave, but with wavelengths from millimetres to many metres. Radio telescopes collect this faint energy to study things light cannot show us: the cold hydrogen gas that fills our galaxy, the active Sun, the remains of exploded stars and galaxies billions of light-years away.
Earth's atmosphere lets two kinds of waves reach the ground: visible light and a wide band of radio. That is why amateurs can do real radio astronomy from a backyard, day or night, and often through clouds. The National Radio Astronomy Observatory has a good introduction.
Hydrogen in the Milky Way
Hydrogen atoms between the stars give off radio waves at exactly 1420.405752 MHz. With a horn antenna and a small software-defined radio you can map the spiral arms for about $100.
Our horn parts list →Radio galaxies and dead stars
Cygnus A, a distant galaxy with giant radio jets, and Cassiopeia A, the remains of an exploded star, are among the brightest radio sources in the sky. Our 20-foot dishes see them drift through the beam.
When they pass over →A short history
- 1933Karl Jansky, an engineer at Bell Laboratories, finds radio waves coming from the centre of the Milky Way at 20.5 MHz. NRAO
- 1937Grote Reber builds a 31.4-foot dish in his backyard in Wheaton, Illinois. He maps the radio Milky Way and finds bright sources in Cygnus and Cassiopeia. Green Bank Observatory
- 1942Radio waves from the Sun are detected, first by British radar stations in February, then as microwaves by G. C. Southworth at Bell Labs. NASA STEREO
- 1951Harold Ewen and Edward Purcell at Harvard detect the 21-cm hydrogen line on March 25, six years after H. C. van de Hulst predicted it. Nature 168, 356
- 2021CVAS gives both 20-foot dishes at Hobbs matching feeds, the first step toward combining them as an interferometer. Club news
- TodayOur dish data goes on the web as it is recorded. Watch it live
Build your own
A radio telescope on the cheap
Sun Detector 2.0
About $38 + used dishA used 18-inch satellite TV dish and a $38 USB radio on a laptop. Point it at the Sun and watch the power climb, then let the Earth turn and record the Sun drifting through the beam.
- One afternoon to build; works in daylight
- Great for families and classrooms
- Based on the Itty Bitty Telescope by the late Chuck Forster, CVAS and SARA member
Hear the Milky Way
$88 to $375Pick up the 21-cm hydrogen line of our galaxy at 1420.4 MHz: the same science our 20-foot dishes do. Buy the ready-made Discovery Dish kit, or build a horn, a Wi-Fi grid dish or your own dish, with a $50 amplifier.
- A weekend project
- Free software: SDR#, Virgo, ezRA
- Bring it to a work day and we will help you test it
Prices checked October 20, 2026.
From the club
News and projects
December 8, 2021Radio Astronomy Interferometer COMING SOON…EXCITING NEWS!After getting up the East Dish and verifying the signals were good, we went ahead and took down the cantenna on…March 3, 2020Newer and Cheaper Amateur Radio TelescopeThe Horn Antenna seems to be a favorite goto and for good reason. All you need is Aluminum flashing 20″x10, a empty…May 11, 2019The Amateur Radio TelescopeTo build your own Amateur Radio Telescope, you will need a few item to get started. You will need: Antenna --> LNA…
Resources
Where to learn more
Learn
NRAO: what is radio astronomy? SARA beginner's booklet (PDF) Society of Amateur Radio Astronomers (SARA) SARA discussion list The SETI LeagueSoftware
Radio-SkyPipe and Radio Eyes (Radio-Sky Publishing) SDR# software-defined radio RTL-SDR software list Virgo spectrometer ezRA, easy radio astronomy PICTOR, a free online radio telescopeJoin us
Become part of the group
The radio group is part of the Chippewa Valley Astronomical Society. CVAS membership is open to anyone with an interest in astronomy, from beginners to engineers.
- $20Individual
- $25Family
- $10Full-time student
Yearly dues, January to December, as listed on the CVAS membership page in October 2026. Join online or by mail there.
Not ready to join? Come to a work day, or send us a message: questions about building your own telescope are always welcome.