Emission Designators Explained: J3E, A1A, F3E and More

Sooner or later, every radio amateur meets a short code that looks like a licence plate for a signal: J3E, A1A, F3E or 2K70J3E. The code is an emission designator, and it describes a transmission precisely in a few characters. It appears in licence conditions in many countries, in equipment manuals, in band plans and in regulations, and it is a handy way to say exactly what kind of signal a transmitter produces. This guide shows how to read one, lists the common codes for amateur radio modes and explains why a single mode can sometimes have more than one valid designator. The descriptions follow the classification used by the International Telecommunication Union, as summarised in a public reference article.

What an Emission Designator Is

According to the reference article on types of radio emissions, the ITU uses an internationally agreed system for classifying radio frequency signals. Each type of emission is classified by its bandwidth, its method of modulation, the nature of the modulating signal and the type of information transmitted on the carrier. It is based on the characteristics of the signal and not on the transmitter used. This is an important point: a designator describes what is on the air, not how the radio makes it. The system was agreed at the 1979 World Administrative Radio Conference, and the Radio Regulations that use it came into force on 1 January 1982.

The Structure: BBBB 1 2 3 4 5

A designator has the form BBBB 123 45, where BBBB is the bandwidth, and the digits and letters that follow describe the signal. The first three of those characters are the ones that you will see most often. The fourth and fifth are optional.

1. Bandwidth (BBBB). Four characters, made of three digits and one letter. The letter takes the place of a decimal point and shows the unit: H for hertz, K for kilohertz, M for megahertz and G for gigahertz. So 500H means 500 Hz and 2M50 means 2.5 MHz. The first character must be a digit from 1 to 9 or the letter H.
2. Type of modulation (1). A letter. It refers to the main carrier and does not include any subcarriers.
3. Type of modulating signal (2). A digit.
4. Type of transmitted information (3). A letter.
5. Details of the information (4). An optional letter with practical details.
6. Multiplexing (5). An optional letter that gives the method of multiplexing.

For amateur use, the three-character core, such as J3E, tells you almost everything, and many documents leave out the bandwidth and the optional fields.

Modulation Letters

The first letter of the core describes the modulation. Those most relevant to amateur radio are as follows.

• A: double-sideband amplitude modulation, such as AM broadcasting.
• F: frequency modulation, such as FM broadcasting and most VHF voice.
• G: phase modulation.
• H: single sideband with full carrier.
• J: single sideband with suppressed carrier, used by shortwave utility and amateur stations. The principle is explained in the article on single-sideband modulation.
• N: an unmodulated carrier, a steady single-frequency signal.
• R: single sideband with reduced or variable carrier.

There are other letters, for example B for independent sideband, C for vestigial sideband, and several for pulse modulation, but you will rarely meet them on the ham bands. For a discussion of sideband choice in practice, see our guide to USB versus LSB.

The Modulating Signal Digit

The second character is a digit that tells you what kind of signal modulates the carrier.

• 0: no modulating signal.
• 1: one channel containing digital information, with no subcarrier.
• 2: one channel containing digital information, using a subcarrier.
• 3: one channel containing analogue information.
• 7: more than one channel containing digital information.
• 8: more than one channel containing analogue information.
• 9: a combination of analogue and digital channels.

The reference article adds that the types 4 and 5, which once indicated facsimile and video, were removed from use with the 1982 Radio Regulations. If you see them in an old document, it refers to the earlier system.

The Information Letter

The third character says what is being sent.

• A: aural telegraphy, intended to be decoded by ear, such as Morse code.
• B: electronic telegraphy, intended to be decoded by a machine, such as radioteletype and digital modes.
• C: facsimile, meaning still images.
• D: data transmission, telemetry or telecommand.
• E: telephony, meaning voice or music for a human listener.
• F: video, such as television.
• N: no transmitted information other than the existence of the signal.

Common Designators for Amateur Modes

Putting the pieces together gives the codes you will see most often. The table lists those given in the reference article for modes used by amateurs, together with a plain-language reading.

The reference article also lists 20K0F3E as wide FM, with a bandwidth of 20.0 kHz and a deviation of plus or minus 5 kHz, still widely used in amateur radio, weather radio, marine and aviation. It lists 11K2F3E as narrow FM with a bandwidth of 11.25 kHz, which in the United States became required for land mobile users above 50 MHz from 1 January 2013, and 6K00F3E as even narrower FM. Those are examples of how the bandwidth part gives a specific channel width to the same F3E signal.

Reading a Full Designator

Take 20K0F3E. The bandwidth part, 20K0, means 20.0 kHz. The F means frequency modulation. The 3 means one channel of analogue information. The E means telephony, so this is FM voice with a 20 kHz channel. In the same way, a CW signal with a bandwidth of 150 Hz would be written 150HA1A: 150H for 150 hertz, A for amplitude modulation of the carrier, 1 for one digital channel without a subcarrier, and A for aural telegraphy. A single sideband voice signal that occupies about 2.7 kHz can be written 2K70J3E. These two examples are built from the rules in the reference article, and the bandwidths are only illustrations, not licence figures.

The bandwidth part is not the same as the setting of the receiver filter. It describes the occupied bandwidth of the emission as defined in the regulations. If you want to understand how to choose a filter for a given mode, our guide to receive filter bandwidth covers the practical side. For the effect of a poor signal on its neighbours, see our article on key clicks and splatter.

Why One Mode Can Have Several Designators

The reference article warns that there is some overlap between signal types, so a transmission may legitimately be described by two or more designators, with a preferred conventional designator in most cases. A good example is data modes sent through an SSB transmitter. A note in the article says that the designators F1B and F1D should be used for frequency-shift keying telegraphy and data, regardless of how the signal is generated, whether by audio FSK into an SSB transmitter or by direct FSK on an FM transmitter. Occasionally, J2B and J2D are used for FSK signals produced by audio modulation of an SSB transmitter. This explains why you may see PSK31 listed as J2B in one document and as a different code in another. If you need a designator for a licence application or a form, use the one that your regulator or the equipment manual specifies.

Where You Will See Designators

• Licence conditions. Some countries list the emission classes that an amateur licence permits, using designators. If your licence lists them, you can check that a new mode fits.
• Band plans. Band plans divide a band by mode, and some of them use designators or the names of modes. Our article on the IARU band plan explains how the segments are organised.
• Equipment specifications. Manuals and type approval documents often list emission designators for a transmitter.
• Event applications. Applications for special permits and temporary licences often ask for designators with bandwidths.

Whenever a designator appears in a rule, read it as a description of the signal, not as a name of the radio or the software. A modern transceiver may generate the same designator in different ways, and the regulator is interested in what the signal does.

Common Mistakes When Reading Designators

• Confusing the digit with the number of channels in an analogue sense. The digit 3 means one channel of analogue information, not three channels. Several channels are shown by 7, 8 or 9.
• Reading the bandwidth letter as part of the mode. In 2K70J3E, the K belongs to the bandwidth. It means kilohertz and sits where the decimal point would be.
• Assuming the transmitter decides the designator. The code describes the signal, so the same designator can come from different equipment.
• Using old classes. Older documents may refer to types that were removed in 1982, such as the digits 4 and 5, or may use a different system altogether. Check the date of the document.
• Treating the optional letters as required. The fourth and fifth characters are optional, so a short code such as J3E is complete for most purposes.

Why It Matters for Operators

You do not need to memorise the whole table, but knowing the structure helps in practical ways. When you read a licence or a band plan, you can check at once whether a mode is allowed in a given segment. When you buy equipment, you can compare what the manual says the transmitter produces with what you want to use it for. When you apply for a special event permit or discuss interference with a neighbour or a regulator, you can describe your signal exactly, which is much clearer than saying that it is digital. And when you help a newcomer, the designator gives a short, universal name for the signal they are hearing. For a broader view of how modes share a band, our guide to digital modes beyond FT8 compares the modes that you are most likely to meet.

Quick Tips for Remembering the Letters

1. Start with the last letter. A means Morse code by ear, B means machine-decoded data modes, E means voice, and D means data or telemetry.
2. The digit tells you whether it is digital or analogue. 1 and 2 are digital, 3 is analogue.
3. The first letter tells you the modulation. A for AM, F for FM, J for SSB with a suppressed carrier.
4. Add the bandwidth. If a document gives the bandwidth, it comes first and uses a letter in place of the decimal point.

The Bottom Line

An emission designator is a compact, internationally agreed description of a signal: a four-character bandwidth code, a modulation letter, a digit for the type of modulating signal and a letter for the information carried. J3E is SSB voice, A1A is CW, F3E is FM voice, F1B is RTTY-style frequency-shift keying and J2B is phase-shift keying such as PSK31. Overlap between types means a mode may have more than one valid code, so always check the one that your regulator or manual uses, and you will be able to read the rules and band plans with confidence.

Frequently Asked Questions

What does J3E mean?

J is single sideband with suppressed carrier, 3 is one channel of analogue information and E is telephony. Together, J3E is the code for SSB voice.

What is the designator for CW?

A1A is the designator for CW keyed directly on and off. The A is amplitude modulation of the carrier, the 1 is one digital channel with no subcarrier and the final A is aural telegraphy. It is often but not necessarily Morse code.

What does the bandwidth part mean?

The first four characters show the bandwidth, with a letter in the place of the decimal point. H means hertz, K means kilohertz, M means megahertz and G means gigahertz, so 2K70 is 2.7 kHz and 20K0 is 20.0 kHz.

Is the emission designator the same as the mode?

Not exactly. A designator describes the characteristics of the signal on the air, not the name of the mode or the transmitter that makes it. Several modes can share one designator, and one mode can have more than one.

What is the designator for FM voice?

F3E, where F is frequency modulation, 3 is analogue information and E is telephony. A bandwidth can be added, for example 20K0F3E for wide FM and 11K2F3E for narrow FM.

Why do some documents show different codes for RTTY or PSK31?

Because there is overlap between signal types. The reference article says F1B should be used for frequency-shift keying telegraphy, but J2B is sometimes used when the signal is made by audio modulation of an SSB transmitter. Follow the code required by the document you are completing.