Linux and GPS Time for FT8
2023-05-20 by Rev. Fr. Robert Bower
One thing you need for FT8 is accurate time on your computer. Keeping accurate time on a Linux based operating system is quite easy today when your computer has access to the Internet. Most modern Linux distributions do it out of the box and no one thinks about it. Even in the field if you are connected to the Internet your computer has an accurate time, if it doesn't, with a quick trip to https://time.is/ you can set your computer's time with a click of a button.
What if you don't have Internet access? The answer is to use GPS time. Linux distributions use either timedatectl/timesyncd, chrony, or NTP. The first listed option timedatectl/timesyncd does not support GPS time which leaves chrony or NTP. Either chrony or NTP will work. On my laptop that I use for POTA is currently running Ubuntu 22.04.1 LTS so I opted for chrony.
Things you will need for this project is a GPS dongle or an Android phone running GPSshare and a computer running a Linux based operating system.
If you use a GPS dongle use one with Pulse-Per-Second (PPS) support for the most accurate time. You can use one without PPS but your time may not be as accurate.
Rather than using a dongle I used my Android phone running GPSshare. My phone's GPS does not support PPS so if you go the phone route realize you will not have as accurate time as with a GPS that supports PPS.
What I did was based on https://ubuntu.com/server/docs/network-ntp.
- I installed the following packages gpsd, chrony, pps-tools, and gpsd-clients on my laptop.
- I installed GPSshare on my phone.
- I already had this done but turn on ADB on your Android phone and install the ADB packages for your distribution.
- If you are running Apparmour disable it for both gpsd and chrony. There seems to be a bug that currently is not fixed in apparmor that blocks gpsd and chrony.
- Use the following guide to setup Share GPS via UBS http://jillybunch.com/sharegps/nmea-usb-linux.html
- Edit /etc/default/gpsd to include the following if you use Share GPS.
DEVICES="tcp://localhost:20175"
# Other options you want to pass to gpsd
GPSD_OPTIONS="-n -b"
# Automatically hot add/remove USB GPS devices via gpsdctl
USBAUTO="true"
- Edit /etc/chrony/chrony.conf to include the following if you are using GPS Share
refclock SHM 0 refid GPS precision 1e-1 offset 0.9999 delay 0.2
driftfile /var/db/chrony/chrony.drift
bindcmdaddress /var/run/chrony/chrony.sock
rtcsync
- Assuming you have Share GPS setup, running, and connected to your laptop, now restart both gpsd and chrony with
sudo systemctl restart gpsd.serviceandsudo systemctl restart chrony.service - Now run chronyc sources
You should see something like
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
#? GPS 0 4 177 24 +21ms[ +17ms] +/- 200ms
^- prod-ntp-4.ntp1.ps5.cano> 2 10 377 29m +833us[ +833us] +/- 48ms
^- prod-ntp-3.ntp4.ps5.cano> 2 10 377 969 +1240us[+1240us] +/- 51ms
^- prod-ntp-3.ntp1.ps5.cano> 2 10 377 777 +1991us[+1991us] +/- 51ms
^- alphyn.canonical.com 2 10 377 998 +1522us[+1522us] +/- 80ms
^- 44.190.40.123 2 10 357 1004 +2127us[+2127us] +/- 81ms
^- pittsburghmusicals.com 3 10 377 982 +1632us[+1632us] +/- 58ms
^+ ntp1.glypnod.com 2 10 377 923 +1561us[+1561us] +/- 37ms
^+ ntp01.nonexiste.net 1 10 377 21m -6787us[-6787us] +/- 32ms
^- srv11.dynamigs.net 2 10 377 33m +24ms[ +24ms] +/- 125ms
^+ triton.ellipse.net 2 10 377 44 +6464us[+6464us] +/- 27ms
^- srcf-ntp.stanford.edu 2 10 377 26m +4218us[+4218us] +/- 37ms
^* 140.99.199.146 2 10 377 31m +501us[ +539us] +/- 14ms
Showing that the GPS is providing time and everything is working.
Remember using your phone's GPS works but a GPS dongle with PPS support would even be better.