OnAirWeather & science · Experimental
Decode HRPT / AHRPT with an SDR
OnAir receives HRPT / AHRPT. HRPT / AHRPT weather satellite pictures near 1.7 GHz: MetOp-B / MetOp-C AHRPT (QPSK 2.33 Msym/s, 1701.3 MHz) with the AVHRR channels growing line by line, FY-3 AHRPT (about 2.8 Msym/s, frames counted only) and the retired NOAA HRPT (BPSK, Manchester, 665.4 kbit/s). Needs a dish (about 1 m or more, tracking the satellite) with an LNA at the feed and a fast radio (4 Msps or more: HackRF, Airspy, SDRplay, Pluto; not an RTL-SDR).
What HRPT / AHRPT is
HRPT and AHRPT are the high-resolution direct broadcast of polar weather satellites (MetOp, FY-3, formerly NOAA), carrying the full AVHRR image data.
Frequencies and where it is used
MetOp-B / -C AHRPT on 1701.3 MHz (QPSK 2.33 Msym/s, K = 7 Viterbi, Reed-Solomon (255,223) x 4, CCSDS packets, AVHRR lines), FY-3 AHRPT (QPSK, frames counted only), retired NOAA HRPT (BPSK, Manchester, 665.4 kbit/s).
In OnAir the tuning shortcut is Weather pictures, 1.7 GHz; you can enter any frequency your radio reaches.
What OnAir shows for HRPT / AHRPT
The AVHRR picture grows line by line (colour or one of five channels), saved as PNG. Needs a dish (about 1 m or more, following the satellite) with an LNA at the feed and a fast radio (4 Msps or more; not an RTL-SDR). NOAA-15, 18 and 19 are retired.
This receiver is built from the published specification and checked end to end on simulated signals. It has had little or no testing on real transmissions yet, so reports and recordings on Discord are welcome.
Which radio you need
This mode sits at a high frequency, so check that your radio tunes it: a HackRF covers 1 MHz to 6 GHz, and RTL-SDR stops near 1.7 GHz. Some modes at these frequencies also need a fast radio (10 to 20 Msps) or a dish and an LNB.
Questions about HRPT / AHRPT
Can I decode HRPT / AHRPT with an RTL-SDR?
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.
Is it legal to receive HRPT / AHRPT?
Receiving these signals is legal in most countries. OnAir is a receiver.
Can I try HRPT / AHRPT in OnAir without a radio?
Yes. Most modes include a built-in synthetic test signal, so you can open the screen and try the controls before you own a radio.
Try it without a radio
OnAir includes built-in synthetic test signals for most modes, so you can open this screen, see the layout and try the controls before you own a radio. The Tour button walks you through the app.