CCW (Coherent CW)

The coherent CW is a pure digital mode because it is only done for computers (although it is readable by a human being). The keying produced by the computer is perfect so as to allow synchronization and correct evaluation of the bit (dot or dot abscence).


Created by: Ramond 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). An idling character (.......) has been added. It is specific to the CCW (of Multipsk) to keep the synchronization in case of absence of characters to send. A carriage return is transformed in a space followed by an idling character.
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).