Notes on setting up ground stations.
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Spacecruft Galmon

Notes on setting up ground stations.


Galmon is a system to monitor GNSS. Ground stations on Earth use galmon software to collect data from each GNSS satellite.

Main website:

Source code:


Ground Stations

There are two main GNSS chipsets that the galmon software support. UBX and Septentrio. The former is more widely used and easier to set up.


Using these devices are as easy as installing galmon software and running the startup script. No device configuration is needed. There are a variety of UBX devices, the ones below use the U-blox ZED-F9 chipset.

U-Blox website:

Ardusimple website:

simpleRTK2B USB. Available at Mouser.

simpleRTK2B-mPCIe. Available at Mouser.

Start devices with options, ala:

cat /etc/default/ubxtool-ttyACM0

DAEMON_OPTS="--owner 'Jeff Moe SpaceCruft' --remark 'Colorado, USA | Traverse Ten64 | simpleRTK2B-mPCIe' --gps --galileo --beidou --glonass --station XXX --destination"


The Septentrio device is available as apparently very high quality standalone (unobtanium?) hardware that can plug directly into ethernet, amongst other configurations. Septentrio also resells their chips to third party integrators that make their own more readily available boards, such as the one used in the following setup.

Septentrio website:

Ardusimple simpleRTK3B with Septentrio mosaic-X5.

Note: in Ardusimple's lineup, the devices with "2" in them, such as simpleRTK2B are UBX, while devices with "3", such as simpleRTK3B are Septentrio.

Manufacturer's part number:

  • AS-RTK3B-MX5-L125-NH-00

Not sold by Sparkfun, adafruit, or Digikey. Mouser part number:

  • 780-ASRTK3BMX5L125NH

HOWTO set up the Septentrio simpleRTK3B USB. This was done using a Traverse Ten64 arm64 with Debian Bullseye (stable/11) as the server. Should be similar for Raspberry Pi or other Debian systems.

Plug in the antenna to the simpleRTK3B. Plug the USB-C into the USB port on the server. Use the USB-C port labeled "GPS", which is the one on the same end as the antenna. This port will supply power to the device. When connected, it creates the following on the server via USB:

  • /dev/ttyACM0 --- Serial port, 8N1 at 115200 baud.
  • /dev/ttyACM1 --- Serial port, 8N1 at 115200 baud.
  • /dev/sr0 --- Emulated CDROM, also accesible via symlink /dev/cdrom.
  • /dev/sda --- Hard drive.
  • usb0 --- USB network interface.

The CDROM drive just contains proprietary drivers. The hard drive is not readable from Debian, at least not initially. By default, the simpleRTK3B device won't send any data. So /dev/ttyACM0 and /dev/ttyACM1 are available, but not streaming any GNSS data.

To configure the simpleRTK3B device, the USB network interface needs to be set up, then the device can be configured via its web interface.

For testing, set up a temporary network interface on the server using the USB network device. For example:

ifconfig usb0 netmask up

Then ping the simpleRTK3B network from the server via the USB device:

ping -c1

If there is a web browser available on the server, it can then access this URL to configure the simpleRTK3B.

If the server is headless, a tunnel can be created from workstation to the server, then the USB web server is available on the workstation via localhost. Create SSH tunnel, where server is the hostname or IP of the server, run this on workstation:

ssh -N -L server

Then on the workstation, the simpleRTK3B Septentrio web configuration tool is available at:

If all is good on the device, it will have already found satellites. It needs to be configured to dump data that galmon will read.

Septentrio simpleRTK3B Web Interface septentrio-simpleRTK3B-www

  • Click mouse on "NMEA/SBF Out" option in the bar.

  • Click "New SBF stream".

  • Under "New SBF Output", select "IP server" and click "Next".

New SBF Output: IP server septentrio-simpleRTK3B-ip-server

  • Select "New IP server connection", click "Next".

  • Set a port, such as 29000 and click "Next". septentrio-simpleRTK3B-port

  • Under "Edit SBF Stream" select the following and click "Finish". Some items may need to be expanded:


Per IRC with ahu, CNAV needs to be enabled on Septentrio too.


When the stream is configured, it should look like the below screenshot. There should be an option in the bottom right to save the configuration for reboot.

Septentrio simpleRTK3B configured with SBF MeasEpoch septentrio-simpleRTK3B-streams-MeasEpoch

Septentrio simpleRTK3B configured with SBF RawNavBits septentrio-simpleRTK3B-streams-RawNavBits

Septentrio simpleRTK3B configured withOUT SBF GAL septentrio-simpleRTK3B-stream-GAL

Septentrio simpleRTK3B configured with SBF PVTCart septentrio-simpleRTK3B-streams-PVTCart

Then create a script that runs septool to consume the web data from the simpleRTK3B. Such as /usr/local/bin/galmon-sept:


septool 								\
	--quiet true							\
	--source					\
	--destination				\
	--station XXX

Create a script to start it: /etc/systemd/system/galmon.service

Description=galmon septool



Then start it:

sudo systemctl start galmon.service
# Check logs:
tail -f /var/log/daemon.log

Start it at boot:

sudo systemctl enable galmon.service

Also, probably want to keep that USB network on reboot. Add this to /etc/network/interfaces, for example:

auto usb0
iface usb0 inet static

Then check if the ground station is appearing here:


Debian galmon builds with source and binaries for arm64 are in the debian/ directory.

Install from Package

Debian package built for Debian Bullseye (11/stable) arm64 architecture:

sudo apt update
sudo apt install libh2o-evloop0.13 libprotobuf23 libwslay1

# Make sure upstream Debian's gpsd package isn't installed,
# or it will mess up dependencies with file conflict:
sudo apt remove gpsd

sudo dpkg -i galmon_0.20220307-1_arm64.deb

Building Debian package

To build the package from source:

sudo apt install ccache build-essential debhelper dpkg-dev help2man   \
    libzstd-dev protobuf-compiler libcurl4-openssl-dev libh2o-evloop-dev \
    libh2o-dev libssl-dev libeigen3-dev libncurses-dev

mkdir galmon-deb
cd galmon-deb

# Grab source, preferably from a reputable source, but this will do:

# Get a debian/ directory souce to make .deb packages, such as:

tar xf galmon_0.20220307.orig.tar.xz
cd galmon_0.20220307

tar xf ../galmon_0.20220307-1.debian.tar.xz

# Edit to taste
vim debian/control
vim debian/changelog

# Build source, perhaps
dpkg-buildpackage -rfakeroot -S -uc -us -sa

# Build binary package:
dpkg-buildpackage -rfakeroot -b -uc

# Install binary package:
cd ..
sudo dpkg -i galmon_0.20220307-1_arm64.deb
# Check apt is happy
sudo apt -f install

To patch in the owner and remark, or it will say the owner is "Septentrio" and there will be no remark.

--- galmon-0.20220307.orig/	2022-04-14 23:06:38.000000000 +0000
+++ galmon-0.20220307/	2022-06-14 23:31:26.962133157 +0000
@@ -376,8 +376,8 @@
-        nmm.mutable_od()->set_owner("Septentrio");
-        nmm.mutable_od()->set_remark("");
+        nmm.mutable_od()->set_owner("Jeff Moe SpaceCruft");
+        nmm.mutable_od()->set_remark("Colorado, USA | Traverse Ten64 | Septentrio simpleRTK3B USB");
         nmm.mutable_od()->set_uptime(time(0) - starttime);
         ns.emitNMM( nmm);

Everything "appears" to be working, but the Septentrio system is logging many CRC errors like:

F/NAV CRC error, skipping
I/NAV CRC error, skipping


See the script scripts/galmonmonmon to check ground station status.


Three ground stations running.

simpleRTK2B-mPCIe, puck antenna, low in canyon.

simpleRTK2B USB, Calibrated Survey GNSS Tripleband + L-band antenna, higher in canyon.

Septentrio. simpleRTK3B. Calibrated Survey GNSS Tripleband + L-band antenna, higher in canyon.

License / Copyright


Unofficial project, not part of official galmon software or website. Upstream sources under their respective copyrights.

Copyright (C) 2022 Jeff Moe.

License: CC By SA 4.0 International and/or GPLv3+ at your discretion.