ARRL International Digital Contest: FT8, FT4 and Grid Exchange
Most contest talk is about CW and SSB, but one weekend a year belongs to the computer modes. The ARRL Digital Contest, formally the ARRL International Digital Contest, invites amateurs worldwide to exchange four-digit grid squares using any digital mode except RTTY, which in practice means FT8 and FT4 for nearly everyone. This guide summarizes the official ARRL page and the WSJT-X documentation: when the contest runs, who can work whom, what counts as legal operation, how the unusual off-time rule works, which sub-bands the ARRL recommends, and how to set up your software so that the exchange is generated for you.
What the Contest Is
According to the ARRL contest page, the objective is for amateurs worldwide to contact and exchange QSO information with other amateurs using any digital mode, excluding RTTY, that supports the four-digit grid square exchange. Operation must be attended. The bands are 160, 80, 40, 20, 15, 10 and 6 meters, and any station may work any other station. In the US, Technician licensees are limited by FCC rules to the 10 and 6 meter bands. Each station may be worked once per band, regardless of mode.
Notice what is missing: there is no separate score for each mode, because one contact per band is all you get. That keeps the contest simple, and it places the emphasis on activity and on covering as many bands as possible. The exchange itself is the grid square, so if you are unsure what that means, our guide to grid squares and the Maidenhead locator system is a good starting point, and the Wikipedia article on the Maidenhead Locator System gives the background.
Dates and Contest Period
The contest runs on the first full weekend of June. It begins at 1800 UTC on Saturday and ends at 2359 UTC on Sunday, a period of 30 hours. The ARRL page links to the contest calendar for the exact dates each year. The rules are maintained as a single downloadable document, the complete ARRL International Digital Contest rules in PDF form, which also contains the scoring rules; read it before your first contest, because this article does not reproduce the scoring formula.
Attended Operation Only
The most important rule for FT8 operators is that automated operation is not permitted. Each claimed contact must include contemporaneous direct initiation by the operator on both sides of the contact. In plain language, you must be at the keyboard and you must start your own contact. Letting software call CQ and work stations unattended does not count. WSJT-X is designed with this in mind, because its documentation says that auto-sequencing is an operator aid and not an operator replacement, and that the program will not make consecutive, fully automated QSOs.
The same principle is the reason for caution with any scripts or helper programs. If the program replies to a station without you pressing a button or choosing a message, ask yourself whether that is direct initiation. When in doubt, follow the rules in the PDF and the intent behind them: both operators are actively making the contact.
The Unusual Off-Time Rule
The contest period is 30 hours, but a single-operator station may operate only 24 of them. Multi-operator stations may operate all 30. After the first QSO, up to 6 hours of off time may be taken in one or two breaks before the final QSO is logged. Each off time must be at least 60 minutes long. The log-checking software counts the two longest breaks in your log and uses those as your two off times; additional breaks and breaks shorter than 60 minutes are ignored. The time before your first QSO and after your last QSO does not count as off time.
The log is then checked and scored over the first 24 hours of operating time. You may keep operating after that without penalty, and those QSOs still count for the other operators, so the ARRL asks you not to delete any QSOs after the 24-hour limit. The intent of the two-break rule is to add a strategic element: you cannot take many short breaks, so you have to decide based on local propagation and sleep.
| Plan | Start | Breaks | Valid? |
|---|---|---|---|
| Straight run | 1800 Saturday | None; operate 24 hours straight | Yes |
| Two long breaks | 1900 Saturday | Two breaks of two hours, end at 2300 Sunday | Yes |
| One sleep break | 1800 Saturday | Operate 12 hours, sleep 5.5 hours, finish at 2330 Sunday | Yes |
| Many short breaks | 1800 Saturday | Several 60-minute breaks | Only the first two count toward the 6 hours |
The first three rows are examples taken from the ARRL’s own list of plans that satisfy the rules. If you have never planned rest for a long event, our guide to rest and time management in 24 and 48 hour contests offers a routine that suits these windows.
FT8 and FT4 Sub-bands Recommended by the ARRL
The page lists recommended sub-bands for FT4 and FT8, as of June 2022. Technician licensees in the US are limited to the 10 and 6 meter sub-bands. The recommendations are:
- FT4 (MHz): 1.836-1.840 (avoid WSPR operation on 1.840), 3.580-3.590, 7.080-7.090, 14.080-14.090, 21.080-21.090, 28.080-28.090 and 50.330-50.340.
- FT8 (MHz): 1.840-1.844 (avoid WSPR on 1.840), 3.590-3.600 (no digital above 3600), 7.090-7.100, 14.090-14.100, 21.090-21.100, 28.090-28.100 and 50.340-50.350.
The advice for choosing a frequency is practical. Set the radio dial at the bottom of the sub-band and run your QSOs on audio frequencies within the radio passband, typically 2.5 to 4 kHz wide. If a sub-band becomes crowded, move the dial up in 2 kHz increments, for example 7.080, 7.082, 7.084, 7.086 and 7.088 MHz for FT4. This keeps everyone in the same place so stations can find each other, instead of spreading across the band.
Setting Up WSJT-X for the Contest
WSJT-X handles the exchange for you. The User Guide says that FT4, FT8 and MSK144 support special messages for NA VHF and EU VHF contests, and that FT4 and FT8 also support messages for ARRL Field Day, FT Roundup, WW Digi and the ARRL International Digital Contest. The decoders recognize and decode these messages at any time. To have the program generate the correct messages and do the matching auto-sequencing, select a supported operating activity on the File | Settings | Advanced tab.
The model QSO for the NA VHF Contest and the ARRL International Digital Contest looks like this:
- CQ TEST K1ABC FN42
- K1ABC W9XYZ EN37
- W9XYZ K1ABC R FN42
- K1ABC W9XYZ RRR
- W9XYZ K1ABC 73
Either callsign may have /R appended to indicate a rover in a VHF contest. You can use RR73 in place of RRR, and the final 73 is optional. Every message carries only the callsigns and the grid squares, so a contact is quick. Contest messages are not supported for compound callsigns, which is explained in our guide to nonstandard callsigns in WSJT-X, so if you operate with a prefix or suffix, check how your messages are generated before the contest starts.
Before any contest, make sure the computer clock is accurate and your audio levels are right. Our guide on FT8 time sync covers the clock, and keeping ALC action off your transmit audio is part of good practice.
What a Typical Hour Looks Like
An hour in this contest is quieter than an hour in an SSB contest, and it is easy to underestimate how much work it still takes. You select a band, set the dial to the bottom of the recommended sub-band, and watch the decodes scroll in 15-second periods for FT8 or 7.5-second periods for FT4. Each time you see a station you have not worked on this band, you double-click the decode and the program starts the exchange. A complete contact has about five messages, so with FT8 you can finish roughly one contact per minute, but only if both stations answer promptly and no one else is transmitting on top.
That rhythm explains why the FT4 recommendation exists. FT4 uses 7.5-second sequences and, as the WSJT-X guide says, is especially well suited to radio contesting, so contacts are about twice as fast when the band is quiet. FT8 has more stations on the air and is more sensitive by a few decibels, which helps when conditions are poor. Many operators begin the contest on FT8 for the larger audience and switch to FT4 on a band that has a good number of active stations. Because a station can only be worked once per band regardless of mode, there is no point in working the same call on both modes on the same band.
Station Requirements and Common Problems
You do not need a large station. The modes were built for weak signals, so a modest antenna can bring in many contacts, but there are a few details that decide whether the weekend is pleasant:
- Clock accuracy: a clock that is more than a second or so off means your decodes shrink to almost nothing. Sync before the contest and recheck during it.
- Transmit audio: keep the level low enough that your radio shows no ALC action, because a distorted signal splatters across the narrow sub-band and annoys neighbours.
- Power: awards separate QRP and Low Power, so running high power is not the only way to win an award. Check the PDF rules for the exact power levels and categories.
- Computer load: logging, decoding and a browser on the same machine can slow the decoder. Close what you do not need.
- Dupes: WSJT-X helps you avoid working the same station twice on a band when you use its filter and wait features, but the final check is your own logging program.
Another common problem is not being in the log of the other station. The WSJT-X guide points out that contest QSOs are generally treated as invalid when they appear in one station’s log and not the supposed partner’s, so a contact that you think is complete but the other station never confirmed may be lost. A sensible habit is to wait for the final RRR or RR73 before you start calling someone else.
Logs, Deadlines and Awards
Logs are due within seven days after the end of the event. They must be submitted online, in Cabrillo format, through the ARRL web app at contest-log-submission.arrl.org; paper logs are not accepted. If your software does not export Cabrillo, the ARRL page points to a conversion tool at b4h.net/cabforms where you enter your log data and receive a Cabrillo file. Our guide to Cabrillo logs and the UBN process explains what the checker looks for.
Certificates are awarded to the top QRP and Low Power single-operator scorers, and to the top QRP and Low Power multi-single scorers, in each ARRL/RAC section and each DXCC country other than W and VE. Plaques, if sponsored, are awarded to the top QRP and Low Power entrants in each category overall, in each ARRL division, in Canada and in each DXCC country other than W/VE. The International Digital Contest is also one of the ten ARRL contests designated as Affiliated Club Competition events, so your club can combine members’ scores. Questions go to contests@arrl.org.
Strategy for a First Entry
- Pick a band plan before the start. A 20 meter and 40 meter combination with a switch to 15 or 10 meters when open is a safe base. Remember that 6 meters is part of this contest and can open suddenly in June.
- Use the two-break rule. Plan your sleep for the hours when the bands are weakest where you live, and schedule the two longest breaks there.
- Work every band you can. A station is worth one contact per band, so changing band is often better than calling the same stations again.
- Be present. Because automated operation is not allowed, steady attended operation is what the contest rewards.
- Check your category. Our article on contest categories explains QRP and Low Power, which matter for awards here.
The Bottom Line
The ARRL International Digital Contest is a 30-hour June weekend for FT8, FT4 and other grid-exchanging digital modes, with attended operation only, one contact per band per station, and a two-break off-time rule that limits single operators to 24 hours. Follow the ARRL’s recommended FT4 and FT8 sub-bands, let WSJT-X generate the contest messages from the Advanced settings, submit a Cabrillo log within seven days, and read the rules PDF for scoring. It is a good first contest for anyone who already enjoys digital modes.
Frequently Asked Questions
When is the ARRL Digital Contest held?
On the first full weekend of June, from 1800 UTC Saturday to 2359 UTC Sunday.
Which modes are allowed?
Any digital mode except RTTY that supports the four-digit grid square exchange, such as FT8 and FT4.
Can I let my software run unattended?
No. Automated operation is not permitted; each claimed contact needs contemporaneous direct initiation by the operator on both sides.
How many hours can I operate?
A single operator may operate 24 of the 30 hours, with up to 6 hours of off time in one or two breaks of at least 60 minutes each. Multi-operator stations may operate all 30 hours.
How do I submit my log?
Upload a Cabrillo file through the ARRL web app within seven days after the contest ends. Paper logs are not accepted.
Which bands are used?
160, 80, 40, 20, 15, 10 and 6 meters. US Technician licensees are limited to 10 and 6 meters by FCC rules.