Mfsk-8 And Mfsk-16 - Wavecom W40PC Manual

The software is started in automatic mode by clicking on the "Auto" button or on "Drum
speed" for manual mode. In manual mode the correct display of the image is controlled using
the "Phase" function in the "Options" menu.
The special items "AM-Gain" and "AM-Offset" are placed in the "Demodulator" menu.
Centering of the signal deviation on the bar graph is controlled by adjusting "AM-Offset". In
addition maximum deviation is required on the bar graph. This is done by adjusting "AM-
Gain". It should be noted that these two adjustments are influenced by each other.
Meteosat reception includes a parabolic reflector and receiver. The AF output of the receiver
may be fed directly into the decoder, which converts it into a weather image viewing station
providing excellent image quality.

MFSK-8 and MFSK-16

Parameter
Frequency range
Frequency Europe
System
Baudrate(s)
Modulation
Receiver settings
Signal source(s)
Alphabet
MFSK-8 and MFSK-16 are multi-frequency shift keying digital transmission modes. MFSK-8
uses a set of 32 tones with the equal distance of 7.81 Hz, MFSK-16 a set of 16 tones with the
equal distance of 15.625 Hz. The baudrate of MFSK-8 is 7.81 and that of MFSK-16 is 15.625.
Both modes are used to transmit text file (ASCII file). The ASCII character is first converted to
Varicode, which encodes frequently used characters to short length bit combination and less
frequently used characters to long length bit combination. For example, 'e' is mapped to '1000'
and 'Z' is mapped to '110111000'.
The Varicode bit stream is then coded with a FEC (Forward Error Correction) algorithm. To
combat frequency fading problems during the transmission, the FEC bit stream is interleaved
before it is assigned to tones (source coding).
In both decoders only the center frequency needs to be tuned.
After the center frequency is set, the decoder first synchronizes, most importantly, to the
polarity of signal. It takes for MFSK8 between 5 and 40 seconds, for MFSK16 between 2 and
7 seconds – this mainly depends on the baudrate of the mode. During the sync phase no text
will be output on the screen.
After the decoder is synchronized, it enters the "Traffic" status, the text file will be output on
the screen. The synchronization is kept as long as the MFSK signal is stable. When the noise is
too strong or the signal disappears, the decoder begins to resynchronize – the status changes
from "Traffic" to "Sync".
Tuning a MFSK-8 and MFSK-16 Signal
The only tuning parameter in MFSK-8 and MFSK-16 signal is the center frequency. First
launch the Real-time FFT analysis tool and set "Peak Hold" to "Max Hold" using the Options
menu. After all tones are displayed, determine the minimum and maximum frequency of the
tone set using the cursors. With the center cursor the center frequency may be set more
accurately. Especially for MFSK-8 the center frequency needs to be set precisely, because the
tone distance is only 7.81 Hz.
WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
Value
HF
Amateur frequency: 14 MHz
MFSK
7.81 Baud for MFSK-8, 15.625 Baud for MFSK-
16
SSB
CW, LSB or USB
AF or HF
MFSK Varicode
Transmission Modes • 157