Build your own · prices checked October 20, 2026
You don't need a 20-foot dish to do real radio astronomy. Here are three ways in, all used by amateurs in the last two years: catch the Sun with an 18-inch TV dish, hear the hydrogen of the Milky Way, or start free with a telescope you control online.
Detect the Sun at 12 GHz with a satellite dish and a USB radio. An afternoon to build; works in daylight.
2Pick up the hydrogen line at 1420.4 MHz and measure how the galaxy turns. A kit, a horn, or a dish you build yourself.
3Use a real radio telescope online, join a worldwide network, or follow a course before you buy anything.
Track 1
Based on the Itty Bitty Telescope, designed by the late Chuck Forster, a CVAS member and a member of the Society of Amateur Radio Astronomers (SARA), and later improved by SARA member Kerry Smith. NRAO still uses it with schools. The original read the Sun on a satellite-finder meter; that meter (Channel Master 1004IF) is no longer made, so this version records the Sun on a computer with a $38 USB radio instead.
The dish focuses radio waves onto the LNB (low-noise block converter), which amplifies the 12.2–12.7 GHz satellite band and shifts it down to 950–1450 MHz for ordinary coax (RTL-SDR.com). The USB radio measures how much power arrives: anything warm in front of the dish raises it. The original Itty Bitty Telescope powered its LNB with 12 V from eight AA cells; satellite LNBs are normally fed 13 or 18 V up the coax, which a satellite power inserter does. The radio's own 4.5 V bias tee is too weak for an LNB, so leave it off, and the DC block keeps the LNB voltage out of the radio.
| 18-inch satellite TV dish with its LNB and mount | NRAO used a DirecTV 18-inch dish. Used ones are often free. |
| RTL-SDR Blog V4L USB radio | $37.95 (rtl-sdr.com). Released August 2026 after the V4 sold out. |
| Satellite power inserter with its supply | Puts 13–18 V on the coax for the LNB |
| Inline DC block | Protects the radio from the LNB voltage |
| 75-ohm coax with F connectors, F-to-SMA adapter | The radio has an SMA socket |
| 75-ohm terminators | One for each unused LNB output |
| A base that swivels | 30 × 30 in board, a lazy Susan, screws and glue |
| Laptop | Windows, Mac or Linux |
rtl_power tool writes power to a spreadsheet file every few seconds, for example rtl_power -f 1150M:1250M:1M -i 2 -g 20 sun.csv. Or watch the noise floor rise in SDR#.Never look at the Sun, with or without anything in front of your eyes.
Track 2
Cold hydrogen gas between the stars glows at 1420.4 MHz (21 cm). Point a small dish or horn straight up and let the Earth turn: when the Milky Way passes overhead, the hydrogen appears as a bump in the spectrum, shifted by the gas's motion. IEEE Spectrum's David Schneider used those shifts from a homemade horn to measure how the galaxy rotates, matching professional results.
| Discovery Dish, 70 cm (KrakenRF) | $149 |
| Hydrogen-line feed, amplifier and filter built in, 6 m coax | $125 |
| RTL-SDR Blog V4L (powers the feed through its bias tee) | $37.95 |
| Mast or tripod | your own |
Beam about 21°; the Sun takes — to drift through today. In February 2026 Dr. Kamal Jabbour mapped the Milky Way's hydrogen with one on a motorized mount, and caught a solar flare.
Discovery Dish Setup guide| Nooelec SAWbird+ H1 amplifier + filter (40 dB gain, 0.8 dB noise figure) | $49.95 |
| RTL-SDR Blog V4L | $37.95 |
| Horn (aluminium flashing or foil board) or a 1 m Wi-Fi grid dish | see our club post |
A 1 m grid dish has a beam about 15°. Tip: in December 2025 Alex P found the Discovery Dish feed on a 1 m Wi-Fi grid dish clearly beat a standard feed with a separate amplifier.
SAWbird+ H1 Grid dish how-toAt 1420 MHz the radio waves are 21 cm (8.3 in) long, so a homemade dish does not need to be very precise. The SETI League's rules: the surface may stray up to a tenth of a wavelength (about 2 cm) from the true curve, and mesh holes up to an eighth of a wavelength (about 2.6 cm) still reflect well (accuracy, mesh). That is woodworking accuracy.
A pyramidal horn made of foil-covered foam board or aluminium flashing, with the SAWbird+ H1 and RTL-SDR at its back. Its beam is wider and the signal smaller than a dish's, but the Milky Way's hydrogen still shows up clearly.
Our club's horn post · RTL-SDR.com horn antennaParabola: height = r² ÷ (4 × focal length). Beam ≈ 70 λ/D; gain and Sun signal assume 50% efficiency. Can limits are where the circular waveguide carries only its first mode (TE11 starts at λ/1.706, TM01 at λ/1.306). Probe position is a quarter of the guide wavelength from the closed end; where the focus sits inside the can uses the SETI League feed formula, whose 1420 MHz feed is 15.6 cm wide with a 4.6 cm probe 8.8 cm from the back.
| RTL-SDR Blog V4L | Airspy Mini | |
|---|---|---|
| Price | $37.95 | $99 (Airspy store) to $165 |
| Hydrogen-line sensitivity | The same: behind a 40 dB amplifier the radio adds under 0.2 K of noise | |
| Spectrum seen at once | 2.4 MHz · ±253 km/s | about 5 MHz · ±528 km/s |
| Converter | 8-bit | 12-bit, better with strong interference |
| Clock | 1 ppm (0.30 km/s) | 0.5 ppm (0.15 km/s) |
| Powers the amplifier? | Yes, 4.5 V bias tee | 4.5 V but only 50 mA: power the SAWbird (120 mA) from its USB port |
Start with the RTL-SDR. Step up to the Airspy Mini for wider, cleaner baselines and smoother drift scans (1.4–1.6× less noise in the same time). Sources: Airspy, Airspy quick start, Nooelec.
Track 3
A 1.5 m radio telescope (1300–1700 MHz) that anyone can use free over the web, including for the hydrogen line.
pictortelescope.com →A worldwide network of small hydrogen-line stations that check each other's detections, so local interference can be ruled out.
WOW@Home →Radio astronomy lessons and a lab for community colleges, launched in 2025.
ARISE →Hear radio storms on Jupiter and the Sun with a wire antenna. The current kit (2.1) uses an SDRplay RSP1B radio.
Radio JOVE kits →The Society of Amateur Radio Astronomers: beginner booklet, mailing list and meetings. Chuck Forster's society too.
radio-astronomy.org →Our hydrogen-line data from Hobbs Observatory goes on the web as it is recorded.
Live telescope →Built one? Stuck? Bring it to a work day and test it beside our 20-foot dishes, or send us a message.
Prices from the sellers' own pages on October 20, 2026 (RTL-SDR Blog, Crowd Supply, Nooelec, Airspy store, PileupDX); prices change. Itty Bitty Telescope: NRAO Green Bank, NRAO procedure, IBT manual, Sky & Telescope March 2025. Solar flux: NOAA SWPC from the US Air Force Radio Solar Telescope Network, updated daily. Beam widths use 70 λ/D; Sun signals assume 50% dish efficiency.