CTY.DAT Country Files: How to Keep Your Logger Up to Date

Every time you type a call sign into a logging program and it instantly shows the country, the CQ zone and the continent, a small text file is doing the work: CTY.DAT. It is one of the least glamorous and most important files in amateur radio. It decides whether a contact counts as a new country, which multiplier you get in a contest, which colour a spot has on your band map and whether WSJT-X flags a station as a new DXCC. If the file is out of date, your software can quietly log a station in the wrong place. This guide explains what is in the file, how the format works, how the file is maintained, how to update it in several popular programs and when to choose the larger Big CTY variant.

It is also a lesson in how much of the hobby depends on volunteers. The country files are maintained by one person, published for dozens of programs and updated whenever a new DX operation makes it necessary.

What CTY.DAT Is

The Amateur Radio Country Files site, maintained by Jim Reisert, AD1C, describes the contest files as the data that contest logging software and other programs use to determine country multipliers from a call sign. The files are updated regularly through the year, and changes are announced on contest and logging software reflectors. The site provides versions of the data for many programs, including N1MM, Win-Test, WriteLog, DXLog, Fldigi and WSJT-X.

CTY.DAT itself is a plain text file. The format description explains that CTY.DAT is the format for CT version 9, and it includes more information than the older per-country files, which allows a program to calculate beam headings and sun times in real time. A single file can be used for all DX contests. The data the program needs to know about an entity includes:

• the country name;
• the CQ zone and ITU zone;
• the two-letter continent abbreviation;
• latitude and longitude;
• the local time offset from UTC;
• the primary DXCC prefix, followed by a list of alias prefixes and individual call signs.

How the Format Works

Each entity occupies a header line with fixed columns, ended with colons, followed by lines of prefixes. Several details matter in practice:

• Primary prefix and aliases. The primary DXCC prefix identifies the entity. A prefix that starts with an asterisk means that the country is on the DARC WAE list and counts in CQ-sponsored contests, but not in ARRL-sponsored contests.
• Exact call signs. If an alias begins with an equals sign, it is treated as a full call sign that must match exactly. This is how exceptions are handled.
• Overrides. Special characters after an alias change a single value: parentheses override the CQ zone, square brackets the ITU zone, angle brackets the latitude and longitude, curly braces the continent and tildes the time offset.
• Order matters. Software is expected to read the file from top to bottom, and if a duplicate call sign appears, the second one is ignored.

The format description also explains that a call sign can be associated with more than one entity. The example it gives is 4U1VIC, which counts as Austria in the ARRL DX contests but as a unique multiplier in the CQ World Wide contests. That kind of detail is the reason the same call sign may be shown differently in two programs, or in the same program with different contest settings. The format page also lists known limitations, such as continents that can only be overridden by country in an older program, which affects the part of Turkey in Europe and a few prefixes in Zone 33.

Why an Old File Causes Real Problems

The world of DX changes constantly. New entities appear, others are deleted, and expeditions use call signs that must be mapped to the right place. The current country file site shows how active the process is: its latest releases are dated 26 August, 6 September and 15 September 2026, each named after the entity that triggered it. The newest release lists “Rotuma Island, 3D2/R” as its version entity, and the accompanying counts file reports 340 current DXCC entities and 62 deleted ones.

If your file is old, the consequences include:

• Wrong multipliers. A new entity is logged as the parent country, and you miss a multiplier in a contest.
• Wrong awards data. Contacts exported to an award tracker may be credited to the wrong entity.
• Misleading colours and alerts. A band map or a program such as WSJT-X may fail to flag a rare entity as new.
• Log checking mismatches. The contest sponsor may check against a newer list, and your claimed multipliers may not match.

Our introduction to how DXCC works explains the entity list itself, and the article on CQ zones and ITU zones shows how zones can create or remove multipliers.

How to Update the File in Common Programs

The country files site publishes download instructions for each program. A summary of the instructions follows, but always read the current page for your version, because menus change between releases.

The pages for each logger also include notes on special cases. If your program is not on the list, look at its manual for a country file or “prefix file” setting. For help with setting up your contest logger in the first place, see our guide to N1MM Logger+ setup, and for the digital side, see WSJT-X and FT8 setup.

When to Update, and When Not To

1. Before a contest or award push. Update a few days ahead, so that you can check that nothing unexpected happened.
2. After a major DXpedition announcement. If a new entity or an unusual call sign is announced, check the country files site for a release.
3. Never in the middle of a contest. A change in the file can change the multipliers or the dupe status of calls in your log, so do not swap it while the contest is running.
4. Keep the old version. Save the previous file in case you need to compare results or restore the earlier behaviour.
5. Re-check the log afterward. After an update, some programs let you recalculate the country information for existing contacts. Review the changes before you export an ADIF file or submit a log.

Moving a log between programs involves country data too. Our article on ADIF explains which fields are exported with each contact.

Big CTY and Everyday Logging

The standard file is designed for contesting, and it contains only a subset of prefixes, with the rest handled by logic in the program. The site also publishes a special version called Big CTY, which is tailored to everyday logging. According to its description, it carries exception call sign data from the start of 2000, and for call signs used more than once only the most recent entity is used. The example given is TO5M, which was used from Martinique in 1993, from Saint Pierre and Miquelon in 1995 and from Reunion in 2004, so logging it today gives Reunion.

Prefixes in Big CTY do not go back in time. They are current as of the release date. If you log an old contact with a call sign from an entity that changed since, it will show the current entity. Big CTY is also a complete file: every prefix that needs a CQ or ITU zone override is listed, which matters for large countries that span several zones, such as the United States, Canada, Australia and China. For that reason it suits a general logbook better than the contest file. The site cautions that some programs store no country information in the log, so a wrong assignment cannot be corrected later except through an override.

Checking That the Update Worked

Never assume an update succeeded. After you replace or import the file, run a quick test. Type the call sign of a recently announced operation into the entry window and see whether the country, zones and continent look right. Try a few ordinary calls from your own country and from a neighbour, to make sure nothing basic broke. If you have the release notes from the country files site, use the entity named in the latest release as a test case, because it is a new or changed entry that an old file would not know.

If something looks wrong, check the date or version shown by the program. Some programs display the country file version in the About box or in a data files window, and a mismatch tells you that the program is still reading an older copy, perhaps from a different folder. Remember that some programs keep a separate copy for each database or profile, so you may need to repeat the import for each one.

Keeping Several Programs Consistent

A modern station often runs more than one program at the same time: a contest logger, a digital mode program, a DX cluster client and perhaps a web logbook. Each has its own idea of the entity list, and each needs its own update. If one program says a station is a new country and another disagrees, the likely cause is a different country file version. Make a short checklist for your station, with the programs that use a country file and the steps to update each, and run through it before major events. Note the date next to each entry, so you can see at a glance which program lags behind.

The same discipline applies to the other reference data in your logger, such as master call sign lists and call history files. Super Check Partial and call history files help in a contest, and the same advice about keeping them current applies to them.

Common Mistakes

• Never updating. Many programs include a country file, but it ages the moment you install it.
• Updating mid-contest. Changes can alter your claimed score.
• Using the wrong variant. A file made for another program may not load in yours.
• Ignoring the manual’s steps. The menu location differs between versions.
• Trusting the colours blindly. A new prefix may not be in your file yet, so check unusual call signs yourself.

The Bottom Line

CTY.DAT is a small file with a large influence on your log. It turns call signs into countries, zones and multipliers, and it must be kept current because the DXCC list and the call signs of expeditions keep changing. Check the Amateur Radio Country Files site before major contests, follow the instructions for your own software, avoid changing the file in the middle of a contest and use Big CTY if you want a more complete file for everyday logging. A few minutes of maintenance protects hours of operating.

Frequently Asked Questions

What is CTY.DAT?

CTY.DAT is a text file that maps call sign prefixes and exceptions to countries, zones, continents and coordinates. Logging and contest programs use it to identify entities and multipliers.

How often is it updated?

It is updated regularly through the year. The three latest releases on the site are dated 26 August, 6 September and 15 September 2026. Check the Amateur Radio Country Files site for the latest version.

Where do I get the file?

From the Amateur Radio Country Files website, which offers versions for many programs, including N1MM, Win-Test, WriteLog, DXLog, Fldigi and WSJT-X, with download instructions for each.

What is the difference between CTY.DAT and Big CTY?

The standard file is tailored to contesting. Big CTY is meant for everyday logging, includes exception call signs from the start of 2000 and lists all prefixes that need zone overrides.

Should I update during a contest?

No. Changing the file can alter multipliers or dupe checks for contacts already in your log. Update before the contest and leave it alone until the log is submitted.

Why does the same call sign show different countries in different programs?

Programs may use different file versions or contest rules. For example, 4U1VIC counts as Austria in the ARRL DX contests but as a separate multiplier in CQ World Wide contests.