Decoding Meteor-M LRPT with a fifteen-dollar dongle
With the last NOAA APT transmitters switched off, Meteor-M is the easiest way to get your own weather images from orbit.
LRPT is a digital QPSK signal at 72 kbit/s around 137.9 MHz. That makes it less forgiving than the old analogue APT: either you have enough signal to lock, or you get nothing at all. The upside is that a good pass gives you a clean, full-resolution image with no static lines.
The chain
QFH antenna → 6 m of RG-6 → LNA with SAW filter → RTL-SDR v4 → SatDump
The filtered LNA made the biggest difference. Without it, a nearby paging transmitter pushed the dongle into overload on every pass and the constellation looked like a cloud.
Settings that worked
| Parameter | Value |
|---|---|
| Sample rate | 1.024 MS/s |
| Gain | 32.8 dB |
| Pipeline | meteor_m2-x_lrpt |
| Minimum elevation | 20° |
Anything under twenty degrees of elevation was a waste of disk space at my location; the rooftop next door blocks the southern horizon.
What is next
Automating the passes with a small scheduler on the Pi, and stitching consecutive passes into one long strip. Notes to follow.