Nonstandard Callsigns in WSJT-X: Compound Calls and Hashes

Sooner or later every FT8 operator sees a decode with angle brackets, such as <PJ4/K1ABC> or a mysterious <…>, and wonders what is going on. The answer lies in how WSJT-X compresses messages, and in what happens when a callsign does not fit the compact pattern. This guide explains nonstandard callsigns: what counts as standard, how compound callsigns such as PJ4/K1ABC and special event calls such as YW18FIFA are handled in FT8, FT4, FST4, MSK144 and Q65, what the angle brackets mean, and what you give up when you use one. All details come from the WSJT-X 3.0 User Guide.

Why FT8 Cares About the Shape of a Callsign

The WSJT-X User Guide explains that all QSO modes use structured messages that compress human-readable information into fixed-length packets. A standard message consists of two 28-bit fields normally used for callsigns, and a 15-bit field for a grid locator, report, acknowledgment or 73. In the modes with 77-bit payloads (FST4, FT4, FT8, Q65 and MSK144) the five extra bits flag special message types for nonstandard callsigns, contest exchanges, FT8 DXpedition mode and a few other possibilities.

The arithmetic is worth seeing, because it shows why some callsigns do not fit. A standard amateur callsign has a one- or two-character prefix, at least one of which must be a letter, followed by a digit and a suffix of one to three letters. Within those rules the number of possible callsigns is 37 x 36 x 10 x 27 x 27 x 27, or somewhat over 262 million. Since 2 to the power 28 is more than 268 million, 28 bits are enough to encode any standard callsign uniquely. Similarly, there are 180 x 180 = 32,400 four-digit Maidenhead grid locators, fewer than 2 to the power 15 (32,768), so a locator needs 15 bits. Anything that does not follow the pattern, such as a call with a country prefix in front or a long suffix, needs a different treatment. Our guide to callsign prefixes shows how varied real callsigns are, and the Wikipedia overview of amateur radio call signs explains the international prefix system that standard patterns are built on.

What Counts as Nonstandard

For the 77-bit modes the guide says that compound callsigns, such as PJ4/K1ABC or K1ABC/3, and special event callsigns, such as YW18FIFA, are supported for normal QSOs but not for contest-style messages. Compound and nonstandard callsigns are recognized and handled automatically by special message types. Most operators never think about it, because WSJT-X generates the right messages by itself. The knowledge matters when something looks odd on the screen or when you plan to operate from abroad or under an unusual call.

The rules for these messages are specific:

• One nonstandard callsign and one standard callsign may appear in most messages, provided that one of them is enclosed in angle brackets.
• If the message includes a grid locator or a numerical signal report, the brackets must enclose the compound or nonstandard callsign. Otherwise the brackets may be around either call.
• Angle brackets mean that the enclosed callsign is not transmitted in full but as a hash code using fewer bits.
• A receiving station displays the full nonstandard callsign if it has been received in full recently. Otherwise it shows the placeholder < . . . >.

These restrictions are honored automatically by the algorithm that generates default messages for minimal QSOs. If you click on decodes and let auto-sequencing do its work, you will not break them.

A Model QSO With a Compound Callsign

The guide gives a model contact between a station operating as PJ4/K1ABC and a station W9XYZ. In the order the messages are sent:

1. CQ PJ4/K1ABC
2. <PJ4/K1ABC> W9XYZ
3. W9XYZ <PJ4/K1ABC> +03
4. <PJ4/K1ABC> W9XYZ R-08
5. <W9XYZ> PJ4/K1ABC RRR
6. PJ4/K1ABC <W9XYZ> 73

Look at how the brackets move. The first call is sent in full so that listening stations learn the full call before a hash stands in for it. After that, whichever call is the nonstandard one is bracketed when a report or locator is sent, and the standard one is bracketed when the roles require it. The point is that each message contains only one full call and one hash, and the receiver fills in the hash from what it has heard before. If your decoder never heard the full call, you see <…> instead.

What You Give Up With a Nonstandard Callsign

The documentation is frank about the cost. Using a nonstandard callsign restricts the types of information that can be included in a message. In particular, it prevents including your locator in standard messages, which impairs tools such as PSK Reporter that rely on grid locators to map your signal. There is also no support for two nonstandard callsigns to work each other, except for the special cases involving /P or /R used in VHF contesting. And contest-style messages are not supported for compound calls.

In practice, this means that a /P or a foreign prefix is not a disaster, but it does make you slightly less visible. If your licence allows you to operate with your normal call (for example, under rules that do not require a prefix), many operators prefer that on FT8. If your authority requires the prefix or suffix, use it; the guide notes that operators with a compound callsign use its full form when calling CQ and possibly also in a 73 transmission, as may be required by licensing authorities. For the legal background see our guide to CEPT licences and operating abroad and our article on portable callsign suffixes.

The Older 72-Bit Modes: Type 1 and Type 2 Compound Calls

The older modes JT4, JT9 and JT65 use a 72-bit payload, and they handle compound callsigns in two ways. Type 1 compound callsigns involve one of about 350 of the most common prefixes and suffixes, which you can display from the Help menu. A single compound callsign of this kind takes the place of the third word of a message, which normally would be a locator, report, RRR or 73. Valid examples are CQ ZA/K1ABC, CQ K1ABC/4 and G0XYZ K1ABC/4. A message that contains a Type 1 compound callsign cannot have a third word, so ZA/K1ABC G0XYZ -22 would be sent without the report.

Prefixes and suffixes that are not on the list use Type 2 compound callsigns. The compound callsign must be the second word of a two- or three-word message, and the first word must be CQ, DE or QRZ. Prefixes can be 1 to 4 characters and suffixes 1 to 3 characters. Valid examples are CQ W4/G0XYZ FM07, QRZ K1ABC/VE6 DO33 and DE W4/G0XYZ 73. A second callsign is never allowed in these messages. In a Type 2 QSO the operators typically send the full compound call when calling CQ and then use the base call and standard structured messages for the rest.

The guide also mentions an option on the File | Settings | General tab, called Message generation for type 2 compound callsign holders, which lets you experiment if you use such a call. For modern FT8 operation most of this detail is behind the scenes, but it explains why old software versions behaved differently.

Practical Settings and Habits

Let the software generate messages

Use the standard message buttons and auto-sequencing. WSJT-X will automatically put the brackets in the right places for the call you entered in Settings. Typing messages by hand is where mistakes happen, such as putting brackets around the wrong call or including a locator that cannot be sent.

Avoid the slash in free text

The guide advises you to avoid the character / in free-text messages, because the program may try to interpret your construction as part of a compound callsign. Free-text messages are limited to 13 characters, including spaces, and are meant for short words such as “TNX ROBERT 73”. WSJT-X is not designed for rag-chewing.

Check your callsign in Settings

Enter your callsign exactly as you will use it on the air. If you are visiting another country, set the full compound callsign before you start. Operators who forget this either transmit a callsign that is not valid in the country they are in or make life harder for the station that is trying to log them.

Expect <…> in busy periods

If you see <…> in place of a callsign, it only means your computer has not recently heard that station transmit its full callsign. Waiting a few periods usually reveals the call. This also explains why a DX station that has just started operating may not appear correctly in your list until you have received a full-callsign message.

A Worked Scenario: Operating From a Holiday Location

Suppose you are licensed in your home country and plan to operate FT8 from a holiday cottage abroad under a reciprocal arrangement that requires a prefix. Before you leave, open File | Settings | General and enter the full compound callsign, including the prefix, exactly as the licensing authority requires. Check that your computer clock is accurate, because a clock error is the most common reason for no decodes, and read the message generated in the first transmit slot to confirm it contains the callsign you expect. WSJT-X shows your outgoing message in the status bar exactly as another station would receive it, which makes this check easy.

When you call CQ you will notice that your grid locator is missing from the standard message, and that replies may show your call with brackets in later messages. Do not be alarmed. Stations that decoded your first transmission will log the full callsign, and stations that join late may only see a placeholder until you transmit again. If the band is busy, you may find that fewer stations answer than at home, and that is a normal consequence of the restrictions rather than a fault in your station. Keep your messages short, log each contact with the callsign you actually transmitted, and upload to your logbook service using that call. If you want to understand how PSK Reporter shows your coverage, remember that spots without a locator are shown with less detail.

The same approach applies if you use a long special event callsign, or a callsign with a suffix like /P that you add for a portable activation. In each case, the software adapts, and your job is to enter the call correctly, leave the message generation alone, and avoid overriding it with hand-typed text.

Special Event Callsigns

Special event callsigns often break the standard pattern, with numbers and many letters, as in the guide’s example YW18FIFA. They work for ordinary QSOs under the same rules as compound calls, but they will not work with contest exchanges, so a special event station that wants to join a contest on FT8 may need to use its regular call in the contest. Our guide to running a special event station explains how these callsigns are obtained and promoted.

Common Mistakes

• Manually removing the angle brackets or adding your own to a message, which makes the message invalid.
• Expecting your grid locator to appear on PSK Reporter when you transmit with a compound callsign.
• Trying to work another nonstandard station in a normal QSO and wondering why the exchange fails; the software does not support two such stations except for /P and /R in VHF contests.
• Using a slash in a free-text message and causing the program to read it as a compound call.
• Assuming that <…> means a problem. It simply means the full call has not been received recently.

The Bottom Line

A standard callsign fits into 28 bits. Anything else, including compound calls with a country prefix or a portable suffix and special event calls, uses special message types and a hash in angle brackets. The result is a working QSO, but without your locator in standard messages, without contest exchanges and without a second nonstandard station on the other end. Let WSJT-X generate the messages, enter your callsign correctly, avoid slashes in free text, and use the full form when your licence conditions require it.

Frequently Asked Questions

What do the angle brackets in an FT8 message mean?

They mean the enclosed callsign is not sent in full but as a hash code with fewer bits. Your computer shows the full call if it has received it recently, otherwise it shows a placeholder.

Which modes handle nonstandard callsigns this way?

The modes with 77-bit payloads: FST4, FT4, FT8, MSK144 and Q65. The older 72-bit modes JT4, JT9 and JT65 use Type 1 and Type 2 compound callsigns instead.

Can I use a compound callsign in a contest on FT8?

The guide says compound callsigns are supported for normal QSOs but not for contest-style messages.

Why does my locator not appear on PSK Reporter?

Using a nonstandard callsign prevents the locator from being included in standard messages, which impairs tools like PSK Reporter.

Can two nonstandard stations work each other?

WSJT-X offers no support for that, except for the special cases involving /P or /R used in VHF contesting.

Should I put a slash in a free-text message?

No. The guide recommends avoiding the slash because the program may try to interpret it as part of a compound callsign.