Mode Radio astronomy

Radio astronomy: the hydrogen line of the Milky Way.

Group	Weather & science
Default sample rate	2.5 Msps
In the mode list	Hydrogen line, 1420 MHz

Step-by-step: Tutorial-Radio-astronomy

What Radio astronomy is

The hydrogen line at 1420.4058 MHz lets amateurs map the Milky Way with a small dish and an SDR.

Frequencies and settings

No decoder: the 21 cm hydrogen line (1420.4058 MHz) and the OH lines.

Setting	Value
Tuning range of the mode table	10 to 6000 MHz
Sample rate asked	2.5 Msps
Lowest working rate	250 ksps
Channel width	2.5 MHz

OnAir takes any frequency you type; the numbers above are the mode's starting point and the range its table describes. In the app the shortcut label is Hydrogen line, 1420 MHz.

What OnAir shows

Long integration of the spectrum (1 s to 1 h, FFT 1024 - 16384), on - off reference or frequency switching, polynomial baseline outside a line window, radial velocity axis (km/s), peak marker, drift-scan waterfall, CSV export, a short how-to (LNA, filter, horn or dish).

Tips and caveats

• This is a tool for looking at the spectrum and recordings, not a decoder of one standard.
• Which radio: Probably not: an RTL-SDR tunes up to about 1.7 GHz. A HackRF (1 MHz to 6 GHz) or another wideband radio is the usual choice for this frequency range.
• Try it without a radio: most modes include a built-in synthetic test signal, so you can open the screen and try the controls first.
• Receiving and the law: Receiving these signals is legal in most countries. OnAir is a receiver. See Legal.

Related pages

• All modes, Weather & science
• Supported radios, Troubleshooting, FAQ
• More in Weather & science: HRPT / AHRPT, NOAA Weather Radio SAME, Radiosonde, Time signals, Ionospheric sounders