MT63 is PSK, and if you go to this link
http://f1ult.free.fr/DIGIMODES/MULTIPSK/MT63_en.htm you can see how the
carriers are fixed in frequency and not random in frequency. In fact,
the description of MT63 is, "DBPSK on 64 carrier tones. The tones are
separated by 7.81 Hz for the 500 Hz bandwidth, 15.625 Hz for the 1000 Hz
bandwidth or 31.25 Hz for the 2000 Hz bandwidth mode. The data is
encoded using a Walsh-Hadamard transform to provide high degree of
redundancy". The tones (i.e. carriers on a SSB transitter) are in a
FIXED place and NOT randomly assigned a frequecy, so MT63 is NOT
frequency hopped, or spread spectrum, even though it can be as wide as
2000 Hz.
The spectrum of MT63 shows this very clearly. Compare that to the
spectrum of ROS 16 and 1 baud of 2250 Hz width.
73 - Skip KH6TY