Tutorial Meteor M LRPT

Tutorial: Meteor-M LRPT

What it is. Meteor-M is a series of Russian polar-orbiting weather satellites. Their LRPT (Low Rate Picture Transmission) downlink sends live pictures of the Earth in several visible and infrared channels, and a small antenna is enough. A pass lasts ten to fifteen minutes; the picture grows line by line as the satellite moves over. This is one of the most rewarding first satellite projects.

What you need

• Radio. Any radio that tunes 137 MHz. The mode asks for 1 Msps; the lowest rate that works is 250 ksps. An RTL-SDR is enough. See Supported-radios.
• Antenna. A circularly polarised antenna with all-sky coverage: a quadrifilar helix (QFH) or a turnstile (crossed dipoles over a reflector) is best; a V-dipole works for high passes. Put it outdoors with a clear horizon, away from noise. A 137 MHz LNA and band-pass filter (also called a "137 MHz filter") at the antenna improve things in cities with strong FM and paging signals.
• Frequencies from the repository's frequency database. Meteor-M LRPT 137.100 MHz and 137.900 MHz (the alternate; the active one changes between satellites and with interference, so check a current list). The mode's default is 137.9 MHz.

Before you start

• Gain: raise it until the noise floor lifts without overload.
• Doppler is up to about 3.5 kHz either way; the receiver follows it. Pass geometry matters more than gain: a pass with a maximum elevation under about 20 degrees is weak.
• Real off-air frames are only partly proven: the mode has been checked with the built-in test signal, and GitHub issue 79 for real passes is open. Recordings of real passes are welcome.

Step by step

1. Set your position (setup wizard or the map).
2. Open View > Passes. Download TLEs (Celestrak or Keplerpass, or a custom server) and find a Meteor-M pass. The list shows Satellite, AOS, LOS, Max el, Duration, Frequency and Mode.
3. Mode list, group Satellite & navigation, entry Weather pictures, 137 MHz.
4. Either press Start a minute before AOS, or tick Auto start at AOS, stop at LOS in the pass planner so it starts the receiver and follows the Doppler. Auto record IQ records the pass.
5. Watch the picture grow.

What you should see

A strip of picture growing line by line, in channels 1 to 6 and a colour composite. Noise at the start and end of the pass, then clean lines. The panel's Modulation list says which variant is in use; Automatic tries OQPSK 72k (N2-3, N2-4), then QPSK 72k, then the interleaved OQPSK 80k mode, until frames decode.

Reading the screen

• Picture. The image view; a view list selects colour or Channel 1 to 6. Colour: channels 1, 2 and 3 as red, green and blue by day, 1, 2 and 5 (infrared) at night; automatic picks from the channels the satellite sends. A channel alone is shown grey.
• Enhancement. As received, Contrast stretch (each channel's own 2 to 98 percent range), Thermal colours (colours a single infrared channel by temperature; pick a channel view) or Stretch + brighten.
• Save PNG saves the picture as shown at full size into the meteor folder of the data folder. New picture starts a fresh one. Auto-save writes a PNG when no new lines have come for 90 seconds.
• Follow scrolls with the newest line.
• Channels table: packets per channel, plus Telemetry (APID 70); State, Frequency, Modulation.
• Night channels option for the infrared composite.

Options and settings

Modulation (automatic or a fixed variant), enhancement, auto-save, follow, the pass planner's auto start and IQ recording.

Troubleshooting

• Noise only. Wrong frequency (137.1 or 137.9, check which is active) or low pass; check the polarity of your antenna.
• Picture with broken lines. Weak signal; improve antenna height or add an LNA.
• No frames decode. Try fixing the modulation instead of automatic.
• FM broadcast breakthrough. Add a filter.
• Doppler lost. Start the receiver at AOS using the pass planner.

Tips

Choose passes with maximum elevation above 40 degrees. Keep the antenna away from computers and chargers.

Legal and privacy notes

Weather satellite images are open broadcasts. Receiving is legal in most countries. See Legal.

Under the hood

OQPSK or QPSK at 72 kbit/s (or the interleaved 80k mode), K = 7 Viterbi, Reed-Solomon, CCSDS packets, MSU-MR image strips with a JPEG-like compression.

Related

Mode-Meteor-M-LRPT, Tutorial-Weather-satellite-images, Tutorial-HRPT-AHRPT, Tutorial-GOES-HRIT, Tutorial-Elektro-L, Troubleshooting