The description done hereafter corresponds to the CCW of Multipsk, which has introduced some modifications (F6CTE/DK5KE) and new modifications in the Multipsk version 3.10.
Click on the copy of the screen in order to
listen to the corresponding audio
signal.
Created by: Raymond Petit (W6GHM) in 1975
Description :
Speed : 12 wpm in standard. Here 12, 24 or 48 wpm respectively corresponding to a dot length of 100, 50 and 25 ms
Modulation : On-Off keying of an audio tone,
Receive mode : indifferent (LSB or USB)
Character set : A..Z 0..9 ? = / + and some others signs more or less used (« Varicode » characters type). The waiting character (-_---) is used as idling character. It is specific to the CCW (of Multipsk) to keep the synchronization in case of absence of characters to send. The line feed character is transformed in a "message start" signal (_-_-_). The removal of a character is done with the transmission of an error character (--------), correction which is taken into account by the receiver.
Shape of pulse : rectangular
Bandwidth : up to about 100 Hz according to speed,
Demodulation : coherent,
Synchronization : automatic using the signal
Correction code : no
Convolution code : no
Interleaving : no
Drift tolerance : 15 to 25 Hz/min (depending on the CCW speed and on the signal-to-noise ratio)
Pmean/Ppeak : 0.5 but very variable
Lowest S/N : the slower is the CCW speed, the better is the decoding.
The minimum S/N ratio depends on the speed and the letters sent. For the standard speed (12 wpm) the minimum S/N is about -12 dB (-8 dB at 24 wpm and -5 dB at 48 wpm).
Note 1 : at the beginning of transmission, "CCW", a space and a waiting character (-_---) are transmitted. The user, to win time, can supress the prefix CCW and its space but the opposite operator will ignore that it is CCW.
Note 2 : in order not to lose the synchronization, it is not possible to type more than one space between two words.