FT8 is a marvel of weak-signal engineering, and it depends on something very ordinary: your computer's clock. If that clock is a couple of seconds off, you can hear a busy band full of signals and decode almost nothing, or you can call someone who never hears you. The fix is usually free and takes a few minutes. This guide explains why timing matters, how to check your own clock, and how to set up dependable time sync on Windows, Mac or Linux.
Why one second matters
FT8 works in fixed 15-second slots. Everyone transmits at the same moments, and everyone else listens during them. A transmission lasts a little under 13 seconds and starts shortly after the slot begins, so the decoder expects the signal to begin at a precise time. If your clock disagrees with the sender's, the decoder is looking in the wrong place. Decoders tolerate some error, but it is a small margin, roughly a second or two either way. Stay well inside it.
What "accurate" really means here
You do not need a laboratory-grade clock. The target is a clock within a fraction of a second of true UTC, and ordinary internet time sync does far better than that. Faster modes are less forgiving. FT4 uses shorter slots of about 7.5 seconds, so timing errors take a bigger bite. Building good habits for FT8 pays off with every other timed digital mode.
Check your clock with the DT column
Your decoding software already tells you how you are doing. In WSJT-X the DT column shows the time offset, in seconds, between each decoded signal and your own clock. Most stations will show values near zero, often within a few tenths of a second either way. Read the pattern:
- Most stations show a similar offset (say, all a half-second or more early or late): your clock is probably off.
- One station shows a large offset while the rest look normal: that station's clock is the problem, not yours.
- Few or no decodes on a band you know is busy: check the clock before blaming the antenna.
Never nudge your own clock to match a single odd station. Trust a reliable time source, not the crowd.
Windows: turn on automatic time and force a sync
Windows keeps time through its built-in time service, and by default it does not check very often, so drift can build up between checks. Open Settings, then Time & language, then Date & time. Make sure the option to set the time automatically is on, and click Sync now. From an administrator command prompt, the command w32tm /resync does the same job. Also confirm the correct time zone is selected, because the display should make sense to you, even though FT8 software works in UTC.
Mac: use the built-in network time setting
On a Mac, open System Settings, choose General, then Date & Time, and turn on the automatic time and date option. macOS uses a time server from Apple by default, and you can change the source if you prefer another. Macs are generally good at staying synced while they have a network connection, so the most common Mac problem is simply an unusual network that blocks time traffic.
Linux: timedatectl and chrony
Most modern distributions sync time automatically. Run timedatectl and look for a line saying the system clock is synchronized. If it is not, timedatectl set-ntp true enables network time. For finer control, install chrony, a widely used time daemon, and run chronyc tracking to see how far your clock is from its source. Many small single-board computers have no battery-backed clock, so they start each boot with the wrong time until the network sync completes. Give them a moment before you transmit.
Third-party tools for stubborn Windows setups
If the built-in Windows sync is too lazy for your liking, dedicated time programs can check more often and show you the current offset. Meinberg's free NTP package is one well-known example, and there are several small utilities aimed at digital-mode operators. Whatever you choose, download it from the developer's own site, read what it changes, and remember that a good tool only replaces the sync schedule, not the need for a working network connection.
GPS time for portable and off-grid operating
Away from home there may be no internet, and a laptop's own clock will slowly wander. GPS satellites broadcast very precise time, and an inexpensive GPS receiver can feed it to your computer. Pairing it with software such as gpsd and chrony on Linux is a popular approach. A receiver that provides a pulse-per-second output gives the best result. A simple USB receiver sending only text data is less precise, but is still well within what FT8 needs. Either way, the receiver needs a reasonable view of the sky. A phone hotspot is a simpler backup for NTP if you have signal.
Common mistakes
- Setting the clock by hand from a wristwatch or phone glance. Manual clocks drift again.
- Trusting a time-zone fix to solve a timing problem. Zone and daylight-saving settings change the display, not the accuracy of the underlying clock.
- Assuming sync is on after a fresh install, a new laptop or a virtual machine. Check it.
- Blocking time traffic with a strict firewall or a captive network that has not finished its login page.
- Syncing once and forgetting it. Recheck before long sessions, especially on a computer that has been asleep.
- Blaming timing for everything. Audio levels, a noisy band or a weak antenna cause plenty of missed decodes as well.
A quick pre-session checklist
- Confirm automatic time is enabled in your operating system.
- Press the sync-now option, or run the sync command.
- Open your decoder and watch DT on a few strong stations.
- Check the band is open with the live HF propagation page before you spend time calling.
- Remember that transmitting requires the right licence, and that rules and privileges differ between Canada and the USA, so follow your local regulations.
Time and your station log
An accurate clock helps beyond decoding. Contact times in your records are UTC, and confirmations only match up when both sides log close to the same time. If you keep your contacts in the free HamRadioList logbook, a synced clock means your entries line up with the other operator's. It also helps if you are new to digital modes: our FT8 beginner walkthrough covers the rest of the setup, and the ham radio FAQ answers common early questions. If you run a computer at a distant station, Remote Rig and Station Bridge are worth reading about, since the shack computer is the one whose clock matters most.
Wrap-up
Good FT8 timing is mostly a matter of turning on automatic sync, forcing a fresh sync now and then, and letting the DT column confirm that things are healthy. Add a GPS receiver if you operate away from the internet. Once the clock is right, you can spend your attention on antennas, bands and conversations instead.
How HamRadioList can help
Once your clock is right, every contact you log carries a trustworthy UTC time, so try the free HamRadioList logbook to keep those contacts organised. Before you start a session, the live HF propagation page shows which bands are open. If you run a shack computer remotely, Remote Rig and Station Bridge are worth a look too.
- Free online ham radio logbook - log every contact, import and export ADIF, sync with QRZ.com and keep your awards organised.
- Live HF propagation - see current band conditions before you call CQ.
- Remote Rig - operate your own radio from anywhere on Android, iPhone, Windows or Linux, with live push-to-talk audio and CAT control.
- Station Bridge - the software that connects your radio, audio interface and computer to Remote Rig.
- Ham radio FAQ - plain answers to the questions new operators ask most.
New here, or getting back on the air? Create your free HamRadioList account to log contacts, check band conditions and practise for your exam, or browse more guides from the blog. HamRadioList is built by amateur radio operators in Nova Scotia for operators everywhere.