CCW (CW cohérente)

Traduction anglaise.

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).

CCW (Coherent CW) has been created, for amateur radio, by Ramond Petit (W6GHM) in 1975. The CCW presented here derives from the "traditional" CCW with some modifications (F6CTE/DK5KE). For example, the standard speed is 12 wpm . Here the user can choose between 12, 24 and 48 wpm.

The minimum S/N ratio can be very low, down to -12 dB for the standard speed of 12 wpm, depending on the speed and the characters sent.

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.

CCW (CW cohérente) 24MPM
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     :
Bandwidth     :
up to about 100 Hz according to speed,
Demodulation     :
Synchronization :
automatic using the signal
Correction code :
Convolution code :
Interleaving :
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.

Recommanded frequencies for CCW(-OOK) (USB)
Il est proposé de choisir, pour la CCW qui est un mode proche de la CW, les fréquences suivantes:
1844, 3561, 7031, 10107, 14061, 21061, 24907, 28061 Khz (fréquences QRP + 1KHz).

Back to the list of modes included in MULTIPSK