KN4YZY

FT8 and FT4 run on a strict schedule. Everyone transmits and listens in the same time slots, so your computer clock has to be close to the real time. The WSJT-X user guide asks for your clock to be within one second of UTC. When it drifts, you’ll see fewer decodes, and people won’t answer you even though your signal is fine. The good news is that it only takes a few minutes to check and fix.

Level: Beginner  |  Time: About 15 minutes  |  Note: Windows steps change a little between Windows 10 and 11, and time programs get updated, so labels may differ slightly on your computer.

What You’ll Need

• Your computer running WSJT-X (free)
• An internet connection, at least long enough to set the clock
• Optional for field and POTA use: a USB GPS receiver, which can set your laptop’s clock with no internet (it needs extra time software, which I’ll cover another day)

Step 1: Check the DT Column

Open WSJT-X and let it decode for a few cycles. In the Band Activity window, the DT column shows the time difference, in seconds, between each station’s signal and your clock. A few stations will always be a little off because their clocks are wrong. But if almost everyone shows the same offset, like +1.4 or -1.2, the problem is your clock, not theirs. Healthy numbers are mostly close to zero.

Step 2: Compare Against a Time Source

A quick second check: open a time-checking website such as time.is, or listen to WWV, and compare it with your computer’s clock. If you’re off by a second or more, keep going.

Step 3: Fix It on Windows

The WSJT-X user guide says the built-in Windows time sync often isn’t good enough, though newer versions of Windows can do the job if they’re set up well. The tool the guide recommends is the free Meinberg NTP client. Install it, accept the default time servers (or pick ones near you), and let it run in the background. It keeps your clock on time all the time, instead of only correcting it now and then.

If you’d rather try Windows’ own setting first, go to the date and time settings, make sure automatic time is on, and click Sync now. Then re-check the DT column after a few minutes of decoding.

Step 4: Mac and Linux

On a Mac, turn on automatic time in the Date & Time settings so it syncs with an internet time server. On Linux, most distributions already run a time service such as chrony or systemd-timesyncd. Make sure it’s enabled and synced.

Gotchas

• Tools that jump the clock. The WSJT-X guide warns against programs that fix the time in sudden steps every so often. A smooth, steady correction like NTP is what you want.
• Laptops in the field. Without internet, the clock drifts. Set it right before you leave home, or use GPS.
• Blaming the radio. If you hear the signals but get no decodes, check DT and the clock before you start changing audio settings.

Your Turn

What do your DT numbers look like right now? Post them in the comments, along with the time program you use. And while you’re on the air this week, don’t forget the weekly challenge: check into a local net (details in Wednesday’s post on the How-To page). Got a digital-mode question? Ask it in the comments.

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