What is MT63
MT63 has the facility for a secondary channel running simultaneously alongside the main channel. This can be put to a variety of uses, such as the generation of a continuous identification or beacon.
The secondary channel is not a prime function of the mode and therefore some software provides for it and others do not. The option to transfer binary files, such as higher-level documents or spreadsheets, is similarly at the whim of the programmer.
MT63 is perhaps the most elaborate user of error correction techniques. It uses a Walsh function that spreads the data bits of each character across all 64 of the tones of the signal spectrum and simultaneously repeats the information over a period of 64 symbols within any one tone. This takes 6.4 seconds.
The combination results in superb impulse noise rejection. At the same time, in the frequency domain, significant portions of the signal can be masked by unwanted noise or other transmissions without any noticeable effect on successful reception.
Transmission speed is good because there are so many individual tones to describe the information, while the individual symbol rate per tone can remain slow (which is good protection against ionospheric disturbances).
Tuning of MT63 modes is not all that critical. This is because the mode can use Forward Error Correction techniques to examine different combinations of the 64 tones that calculate the correct location within the spectrum. As an example, MT63-1K will still work if the decoder is off tune by as much as 100Hz. MT63-2K is even less exacting, with an error of 250Hz being tolerated.
For information on MT63 See the wikipedia entry.