Linux Alternative Time Sync-ing for JS8 or FT8

Question

I was learning about the time drift set and correct features of JS8Call and wondering about an alternative.

Assume I have a wrist watch that loses 1 second a month and that it's been sync-ed to an NTP server manually within 500 ms or better.

Is there a program for Linux that allows one to manually sync the computer time to a watch ?

I imagine this would require knowing the lag from the user input to the actual time update.

Perhaps this question is not on topic. I didn't know where else to ask.

Answer 1

Yes. Chrony is an NTP client which is particularly good at offline behavior (better than ntpd in this regard, and infinitely better than systemd-timesyncd, which is only an SNTP client and not a true NTP client at all). It will generally do a better job of maintaining sync for a machine that is only periodically connected to a network.

For the case of an extended period with no network connectivity (or GPS), chrony has a "manual" mode which can be entered using chronyc manual on, and then at any point you can give it a time hack using chronyc settime (see the docs for more info). Rather than stepping the system clock directly, this does the same kind of smooth adjustment that NTP does, and multiple readings can be used to adjust the system clock drift. This is similar to adjtimex --watch but there are some advantages to having it be in the same program that does your NTP when you're on the network.

And adding some amateur radio relevance: the best source of time for manual entry in many parts of the world if you're doing JS8 is, of course, not your wristwatch, but a radio time signal like WWV, WWVH, CHU, RWM, or BPM. As long as you can hear one, you don't have to worry about it gaining or losing time like your wristwatch.

Answer 2

You don't need accurate time for FT8, just time to approx. the nearest half second to any of any 0, 15, 30, or 45 second mark.

If you look at the computer clock display with a second hand, and the waterfall in high enough time resolution, you can see how far off you. Then manually adjust the clock so that one of 0,15,30,45 displays on the clock shows just before you see fresh stripes on the FT8 waterfall.

Answer 3

that it's been sync-ed to an NTP server manually within 500 ms or better.

NTP is much better, +- 5ms is not even ambitious. So, systemd-timesyncd will do wonders!

You'll want to edit /etc/systemd/timesyncd.conf to set PollIntervalMaxSec= to something reasonable (I'd recommend not going below 120 s). Then, you can activate the service using systemctl enable --now systemd-timesyncd and it will keep your system clock within a few milliseconds of UTC.

(some distros use chronyd instead, same general idea applies, but different config file, and the service is called chronyd instead of systemd-timesyncd.)

But, to come back to your original question:

Assume I have a wrist watch that looses 1 second a month

That's a 0.39 ppm wrist watch. You don't have a 0.39 ppm wrist watch; for such applications, 15 ppm oscillators are more the order in which one moves.

< 1 ppm is oven-controlled oscillator domain, not wristwatch domain, for power reasons. Technically, when you need such precision for a compute/communication system, and it's not underground or to be deployed above 10 km, or in a war zone where that might be disabled, you'd go for a GPS receiver instead. These are commonly available with a Pulse-Per-Second output, and you can read the time at the last pulse from the NMEA strings read from the serial port of the receiver.

Now, you might find yourself in a submarine without access to the sky (but to FT-8? OK!) and need a good clock and time source. Then you'd use a good oven-controlled oscillator to generate e.g. a 2²⁰ Hz clock, or even an atomic clock. You count the seconds according to that clock, and whenever someone whose clock you trust comes by (i.e., someone with a GPS with an OCXO in holdover, your wristwatch's 15ppm paired with the natural 1s resolution is so bad that you stand a fair chance to make things worse, not better), you use a (very slow) control loop to adjust your clock. That way, you train it to be as true as it can long-term be to "real" time.

Is there a program for Linux that allows one to manually sync the computer time to a watch ?

You could write your own few python lines of Python or C or C++ code with OpenCV2 to extract the digits from a picture of your digital wristwatch, and set the time according to that; OpenCV can instead of reading a picture file simply use a webcam, as well.

On a less automated notion, what's wrong with looking at your watch, noticing it's 13:25:03, typing timedatectl set-time "2022-05-24 13:26:00" and hitting enter exactly when that time actually happens? That's terrible in terms of accuracy, but low-effort.