{"id":349,"date":"2026-10-21T01:27:52","date_gmt":"2026-10-21T06:27:52","guid":{"rendered":"https:\/\/radio.cvastro.org\/index.php\/build-a-radio-telescope\/"},"modified":"2026-10-21T01:27:52","modified_gmt":"2026-10-21T06:27:52","slug":"build-a-radio-telescope","status":"publish","type":"page","link":"https:\/\/radio.cvastro.org\/index.php\/build-a-radio-telescope\/","title":{"rendered":"Build a Radio Telescope"},"content":{"rendered":"\t
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Build your own \u00b7 prices checked October 20, 2026<\/p>\n\t\t\t

Build your own radio telescope<\/h1>\n\t\t\t

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.<\/p>\n\t\t\t

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The Sun in radio today<\/span>\u2014<\/b>Loading today's measurement\u2026<\/small><\/div>\n\t\t\t\t
Best time for the Sun today<\/span>\u2014<\/b><\/small><\/div>\n\t\t\t\t
Milky Way straight overhead<\/span>\u2014<\/b><\/small><\/div>\n\t\t\t<\/div>\n\t\t<\/div><\/section>\n\n\t\t
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Sun Detector 2.0<\/h3>About $38 + a used TV dish<\/span>

Detect the Sun at 12 GHz with a satellite dish and a USB radio. An afternoon to build; works in daylight.<\/p><\/a>\n\t\t\t\t2<\/span>

Hear the Milky Way<\/h3>$88 to $375<\/span>

Pick up the hydrogen line at 1420.4 MHz and measure how the galaxy turns. A kit, a horn, or a dish you build yourself.<\/p><\/a>\n\t\t\t\t3<\/span>

Start free<\/h3>$0<\/span>

Use a real radio telescope online, join a worldwide network, or follow a course before you buy anything.<\/p><\/a>\n\t\t\t<\/div>\n\t\t\t

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How strongly each setup sees the Sun today<\/h3>\n\t\t\t\t

Waiting for today's solar measurement\u2026<\/p><\/div>\n\t\t\t\t

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Track 1<\/p>\n\t\t\t

Sun Detector 2.0<\/h2>\n\t\t\t

Based on the Itty Bitty Telescope<\/b>, designed by the late Chuck Forster<\/b>, 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.<\/p>\n\t\t\t

\n\t\t\t\t\n\t\t\t\tLNB<\/text>\n\t\t\t\t18-inch TV dish<\/text>\n\t\t\t\t950\u20131450 MHz<\/text>\n\t\t\t\tPower inserter<\/text>DC up the coax to the LNB<\/text>\n\t\t\t\twall power supply<\/text>\n\t\t\t\t\n\t\t\t\tDC block<\/text>\n\t\t\t\t\n\t\t\t\tUSB radio<\/text>RTL-SDR V4L<\/text>\n\t\t\t\t\n\t\t\t\tLaptop<\/text>logs the power<\/text>\n\t\t\t<\/svg><\/div>\n\t\t\t

The dish focuses radio waves onto the LNB<\/b> (low-noise block converter), which amplifies the 12.2\u201312.7 GHz satellite band and shifts it down to 950\u20131450 MHz for ordinary coax (RTL-SDR.com<\/a>). 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<\/b> does. The radio's own 4.5 V bias tee is too weak for an LNB, so leave it off, and the DC block<\/b> keeps the LNB voltage out of the radio.<\/p>\n\t\t\t

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What you need<\/h3>\n\t\t\t\t\t\n\t\t\t\t\t\t
18-inch satellite TV dish with its LNB and mount<\/td>NRAO used a DirecTV 18-inch dish. Used ones are often free.<\/td><\/tr>\n\t\t\t\t\t\t
RTL-SDR Blog V4L USB radio<\/td>$37.95<\/b> (rtl-sdr.com). Released August 2026 after the V4 sold out.<\/td><\/tr>\n\t\t\t\t\t\t
Satellite power inserter with its supply<\/td>Puts 13\u201318 V on the coax for the LNB<\/td><\/tr>\n\t\t\t\t\t\t
Inline DC block<\/td>Protects the radio from the LNB voltage<\/td><\/tr>\n\t\t\t\t\t\t
75-ohm coax with F connectors, F-to-SMA adapter<\/td>The radio has an SMA socket<\/td><\/tr>\n\t\t\t\t\t\t
75-ohm terminators<\/td>One for each unused LNB output<\/td><\/tr>\n\t\t\t\t\t\t
A base that swivels<\/td>30 \u00d7 30 in board, a lazy Susan, screws and glue<\/td><\/tr>\n\t\t\t\t\t\t
Laptop<\/td>Windows, Mac or Linux<\/td><\/tr>\n\t\t\t\t\t<\/table>\n\t\t\t\t<\/div>\n\t\t\t\t
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Build it<\/h3>\n\t\t\t\t\t
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  1. Make the base.<\/b> Centre the lazy Susan on the board, glue and screw it, and bolt the dish bracket to the turning top so the dish can swing and tilt. Make it heavy enough not to tip.<\/li>\n\t\t\t\t\t\t
  2. Prepare the dish.<\/b> Put a 75-ohm terminator on every LNB output except one, and run coax from that output.<\/li>\n\t\t\t\t\t\t
  3. Connect.<\/b> LNB coax \u2192 the inserter's dish\/LNB port; the inserter's receiver port \u2192 DC block \u2192 adapter \u2192 radio \u2192 laptop. Plug in the inserter.<\/li>\n\t\t\t\t\t\t
  4. Install the software.<\/b> Follow the RTL-SDR quick-start guide<\/a> (the V4-series radios need the RTL-SDR Blog drivers). Turn automatic gain off and set a fixed gain.<\/li>\n\t\t\t\t\t\t
  5. Log the power.<\/b> The free rtl_power<\/code> tool writes power to a spreadsheet file every few seconds, for example rtl_power -f 1150M:1250M:1M -i 2 -g 20 sun.csv<\/code>. Or watch the noise floor rise in SDR#.<\/li>\n\t\t\t\t\t<\/ol>\n\t\t\t\t<\/div>\n\t\t\t<\/div>\n\t\t\t
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    Find the Sun<\/h3>\n\t\t\t\t\t

    Never look at the Sun<\/b>, with or without anything in front of your eyes.<\/p>\n\t\t\t\t\t

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    1. Read empty sky first.<\/b> Point at clear sky away from the Sun, trees and buildings. Note the power.<\/li>\n\t\t\t\t\t\t
    2. Aim by shadow.<\/b> Turn and tilt until the LNB's shadow falls in the middle of the dish. The power rises as you get close.<\/li>\n\t\t\t\t\t\t
    3. Peak it.<\/b> Small moves until the power is highest: you are on the Sun.<\/li>\n\t\t\t\t\t\t
    4. Let the Earth turn.<\/b> Swing a little west of the Sun and leave it. The Sun drifts through in about 15 minutes<\/b> today, and your log shows a smooth hill.<\/li>\n\t\t\t\t\t<\/ol>\n\t\t\t\t<\/div>\n\t\t\t\t
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      Today's numbers for an 18-inch dish<\/h3>\n\t\t\t\t\t