From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Spectrogram of MT63-1K Modulation

MT63 is a digital radio modulation mode for transmission in high-noise situations developed by Pawel Jalocha SP9VRC. MT63 is designed for keyboard-to-keyboard conversation modes, on HF amateur radio bands.

Features and Attributes[edit]

MT63 distributes the encoding of each character over a long time period, and over several tones. This code and symbol spreading implementation is key to its robustness under less than ideal conditions. The MT63 mode is very tolerant of mistuning, as most software will handle 120 Hz tuning offsets under normal conditions.

Mode Symbol Rate Typing Speed Duty Cycle Modulation Bandwidth ITU Designation
MT63-500 5 baud 5.0 cps (50 wpm) 80% 64 x 2-PSK 500 Hz 500HJ2DEN
MT63-1000 10 baud 10.0 cps (100 wpm) 80% 64 x 2-PSK 1000 Hz 1K00J2DEN
MT63-2000 20 baud 20.0 cps (200 wpm) 80% 64 x 2-PSK 2000 Hz 2K00J2DEN

MT63 Latency[edit]

One shortcoming of MT63 is that robustness is somewhat compromised with the short interleaver.

Latency (delay between transmitted characters) is more than 6 seconds with the long interleaver.

The typical character transmission delay is 12.8 seconds with Long Interleave Mode.

Mode ECC Mode Latency (sec)
MT63 500 Hz short 12.8
MT63 1K short 6.4
MT63 1K long 12.8
MT63 2K short 3.2
MT63 2K long 6.4
PSK31 - <1


MT63 is seeing a resurgence in its popularity on shortwave with the VOA Radiogram[1] but the software used to encode the text is not using the Varicode that MT63 used in its original design.

Modern software that codes MT63, such as Fldigi, has opted for base128[2] that is essentially ASCII-7. However, the only interleaving options have become long and short, as the medium interleaving mode has become redundant.

MT63 has been mooted as a modulation format for Time Signal Stations, but the implied system does not use Varicode.[3]

See also[edit]


  1. ^ "VOA Radiogram".
  2. ^ "MT63 Modes".
  3. ^ "Wide Area Time Service with Extended Features".

Related links[edit]