Transmission modes

Modes of communication

Amateurs use a variety of voice, text, image, and data communications modes over radio. Generally new modes can be tested in the amateur radio service, although national regulations may require disclosure of a new mode to permit radio licensing authorities to monitor the transmissions. Encryption, for example, is not generally permitted in the Amateur Radio service except for the special purpose of satellite vehicle control uplinks. The following is a partial list of the modes of communication used, where the mode includes both modulation types and operating protocols.

Morse code

Morse code is the original digital data mode. Radio telegraphy which is the direct on/off keying of a continuous wave carrier by Morse code symbols, often called amplitude-shift keying or ASK, may be considered to be an amplitude modulated mode of communications. Although more than 140 years old, bandwidth efficient Morse code, originally developed by Samuel Morse and Alfred Vail in the 1840s, uses techniques that were not more fully understood until much later under the modern rubrics of source coding or data compression. The bandwidth efficiency of Morse code arises because the most used source symbols were accorded the shortest Morse code symbols and the least used were accorded the longest symbols by Vail and Morse. Vail and Morse intuitively understood bandwidth efficiency in code design. It was not until one hundred years later that Claude Shannon’s modern information theory (1948) put Morse and Vail’s Morse code technology on a firm theoretical mathematical footing, that then resulted in similar Morse code-like bandwidth efficient data encoding technologies such as the modern Huffman, Arithmetic and Lempel-Ziv codes. Morse code is still used by amateur radio operators. Operators may either key the code manually using a telegraph key and decode by ear, or they may use computers to send and receive the code.

Analog voice

Decades after the advent of digital amplitude-shift keying (ASK) of radio carriers by Morse symbols, radio technology evolved several methods of analog modulating radio carriers such as: amplitude, frequency and phase modulation by analog waveforms. The first such analog modulating waveforms applied to radio carriers were human voice signals picked up by microphone sensors and applied to the carrier waveforms. The resulting analog voice modes are known today as:

Digital voice

Digital voice modes encode speech into a data stream before transmitting it.

  • APCO P25 – Found in repurposed public safety equipment from multiple vendors. Uses IMBE or AMBE CODEC over C4FM.
  • D-STAR – Open specification with proprietary vocoder system available from Icom, Kenwood, and FlexRadio Systems. Uses AMBE over GMSK with VoIP capabilities.
  • DMR – Found in both commercial and public safety equipment from multiple vendors. Uses AMBE codec over a C4FM modulation variant with TDMA.
  • System Fusion – Open specification with proprietary vocoder system available from Yaesu. Uses AMBE CODEC with C4FM modulation.
  • NXDN Used by Kenwood (Nexedge) and Icom (IDAS)

Image

Image modes consist of sending either video or still images.

Text and data

Most amateur digital modes are transmitted by inserting audio into the microphone input of a radio and using an analog scheme, such as amplitude modulation (AM), frequency modulation (FM), or single-sideband modulation (SSB).

Other modes

Activities known as modes

Certain activities in amateur radio are also commonly referred to as “modes”, even though no one specific modulation scheme is used.