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Satellites

Amateur satellites are repeaters in orbit, weather satellites send pictures, and small science satellites send telemetry anyone may decode. All of them pass overhead for a few minutes at a time, so the work is knowing when, and pointing and tuning while they move.

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The satellite profile carries gpredict for passes and control, SatDump for weather images, gr-satellites for telemetry, and hamlib.

1. Tell gpredict where you are

Every prediction is relative to your position, so it has to be right. Edit → Preferences → General → Ground Stations → Add new. Give it a name and either your latitude and longitude or your Maidenhead locator, and your altitude. Make it the default.

2. Update the orbital elements, every time

gpredict computes passes from orbital elements (TLEs) it downloaded, and they go stale in days. It does not warn you. Edit → Update TLE → From network before any session you care about. A pass that does not happen when predicted is almost always stale elements.

For a trip with no network, update just before you leave: elements a few days old are still good to a minute or so for most amateur satellites.

3. See the passes

The default module shows a map and a list of satellites with their next pass. To follow one: from the module's menu (the small arrow at the top right of the module), Upcoming passes lists the next ones with times, maximum elevation and duration. Passes above about 20° elevation are the ones worth trying with a handheld antenna.

Which satellites are active changes often. Check AMSAT's status page for what is working this week; AMSAT's site also lists each satellite's uplink and downlink.

4. Doppler: let gpredict tune the radio

A satellite moving at orbital speed shifts its frequency by up to about ±3 kHz on 2 m and ±10 kHz on 70 cm across a pass. gpredict corrects for it through hamlib.

  1. Set up rig control with rigctld on 127.0.0.1:4532.
  2. Edit → Preferences → Interfaces → Radios → Add New: host localhost, port 4532, and the radio type: RX only for listening, Duplex for a radio with two VFOs that transmits and receives at once.
  3. From the module's menu, Radio Control. Choose the satellite and its transponder, then Engage and Track. gpredict retunes the radio through the pass.

A rotator works the same way: rotctld from hamlib on port 4533, added under Interfaces → Rotators, then Antenna Control from the module's menu. rotctl -l lists rotator models as rigctl -l lists radios.

5. Weather pictures with SatDump

The American NOAA satellites that sent the classic APT pictures went out of service on 2025-11-09 (not carried). The Russian Meteor-M satellites still send LRPT pictures on 137 MHz, and SatDump decodes them from an RTL-SDR.

  1. Find a Meteor pass in gpredict. If the satellite is not in your module, add it through the module's Configure dialog. Check the current frequency on the satellite's own status pages: they have moved between 137.1 and 137.9 MHz over the years.
  2. In SatDump, Recorder: choose the SDR and the frequency, and the Meteor LRPT pipeline, and start before the satellite rises.
  3. SatDump decodes as it receives and writes the images when the pass ends.

A V-dipole or QFH antenna made for 137 MHz makes the difference between noise and a picture. On a slow laptop, record the pass and process the recording afterwards with SatDump's offline mode, which its manifest notes is the reliable path on modest hardware.

The geostationary weather satellites (GOES, GK-2A) need a dish and a different setup; SatDump decodes them too, and its own documentation walks through it.

6. Telemetry with gr-satellites

gr-satellites decodes the telemetry of hundreds of small satellites from a recording or a live receiver. Its documentation lists them and the command for each. Uploading decoded frames to SatNOGS helps the teams who built them.

What was measured

The profile's members and SatDump's known problems were read from the catalog. The gpredict steps follow gpredict's own documentation, and the Doppler figures are the textbook values for low-orbit satellites. A pass worked or decoded from the field laptop is not yet in the bench record.