is an Orthogonal Frequency Division Multiplexed mode consisting of 64
parallel carriers each carrying part of the transmitted signal.
The tones are differential BPSK modulated. MT63 employs a
unique highly redundant Forward Error Correction system which
contributes to it robustness in the face of interference and facing.
The tones have synchronous symbols, and are raised cosine
moduled. This mode requires a very linear transmitter.
Over-driving leads to excessive bandwidth and poorer reception.
mode is very tolerant of tuning and fldigi will handle as much as 100
Hz of mistuning. This is very important since MT63 is often used
in very low Signal to Noise ratios. There are three standard
||5.0 cps (50 wpm)
||10.0 cps (100 wpm)
||20.0 cps (200 wpm)
In addition there are two interleaver options (short and long) which can be set on the MT63 configuration tab
The default calling mode is MT63-1000. If the short
interleaver is used then one can expect some compromise in robustness.
The long interleaver results in somewhat excessive latency (delay
between overs) for keyboard chatting. MT63-1000 with the long
interleaver has a latency of 12.8 seconds.
can change from receive to transmit immediately upon seeing the other
stations signal disappear from the waterfall. You do not need to
wait until the receive text completes. Any remaining data in the
interleaver will be flushed and the associated receive text printed
quickly to the Rx pane. Tx will commence right after the buffer
MT63 may be operated in the default fixed audio frequency mode. In this mode you are not allowed to randomly place of the
signal on the waterfall. Your transmit signal, and also the
received signal should be centered at 750 Hz for MT63-500, 1000 Hz for
MT63-1000, and 1500 Hz for MT63-2000. If you click on the
waterfall to move the tracking point it will be restored to the
The default mode, MT63-1000, looks like this on fldigi's waterfall.
You can also elect to operate the MT63 modem in a "manual tune" mode (see MT63 configuration tab
The manual tune allows you to place both the Rx and the Tx signal to be
anwhere within the confines of your SSB bandwidth. This screen
shot shows this capability:
This view also demonstrates how immune MT63 is to interference.
The multiple PSK31 signals that appear on top of the MT63 signal did
not degrade the decoder. MT63 is usually used above 14073 MHz to avoid the possibility of this type of mode conflict.
Edited excerpts from Pawel Jalocha's official mt63 code release
The MT63 modem is intended for amateur radio as a conversation (RTTY
like) mode where one station transmits and one or more other stations
can listen. In short, the modem transmits 64 tones in its baudrate specific
differential bipolar phase modulation is used to encode 10 bits of
information per second on each tone. The user data in the form of 7-bit
ASCII characters is encoded as a set of 64-point Walsh functions. The
bits are interleaved over 32 symbols (3.2 seconds) to provide
resistance against both pulse and frequency selective noise or fading. The character rate equals to the
symbols rate thus the modem can transmit 10 7-bit characters per second.
This modem can as well run in two other modes obtained by simple time scaling, the possible modes are summarized here:
|Interleave / Char.
|5 char / sec
|6.4 or 12.8 sec
|10 char / sec
|3.2 or 6.4 sec
|20 char / sec
|1.6 or 3.2 sec
For each mode the interleave factor can be doubled thus each character becomes spread over twice as long period of time.
The MT63 modem is made for single side band operation. The audio
generated by the modem (sound card output) is applied to the SSB
modulator. On the receiver side, the output of the SSB demodulator is
put into the sound card input. The envelope of the MT63 signal is not
constant as in other multi-tone systems - it is rather
noise-like. One must be carefull not to overdrive the transmitter.
The receiver of the MT63 is self-tuning and self-synchronizing thus the
radio operator is only required to tune into the signal with +/- 100 Hz
accuracy. The modem will tell the actual
frequency offset after it is synchronized. The operator should not
to correct this offset unless he is able to tune the radio
receiver very slowly, because MT63 as a low rate phase modulated system cannot tolerate sudden frequency changes.
The MT63 is a synchronous system and it relies on the sampling rate to
be the same at the receiver and the transmitter. At least the sampling
rates should not be different by more that 10^-4.
If you have calibrated your sound card to WWV then you will meet this requirement.