Wavecom W61PC V7.5.0 - Manual (Page 178)

168  Transmission Modes WAVECOM Decoder W61PC/LAN Manual V7.5
Parameter Value
Modulation MFSK-32 / MFSK-16
Symbol rate 7.81 Bd for MFSK-8, 15.625 Bd for MFSK-16
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info MFSK Varicode
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 combinations and less frequently used char-
acters to longer length bit combinations. 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 fre-
quency 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 sig-
nal. This takes for MFSK-8 between 5 and 40 seconds, for MFSK-16 between 2 and 7 seconds – this main-
ly depends on the baud rate of the mode. During the sync phase no text will be output on the screen.
After the decoder is synchronized, it enters the Traffic state, and a text file will be output on the screen.
The synchronization is maintained 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. Set Peak Hold to Max
Hold using the Options menu. After all tones are displayed, determine the minimum and maximum fre-
quency 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 dis-
tance is only 7.81 Hz.
After the decoder has been synchronized, it enters the Traffic phase. The polarity status field on top indi-
cating "N" (for Normal) or "I" (for Inverse) shows whether the MFSK signal is USB (Upper Side Band) or
LSB (Lower Side Band). The transmitted text file is output in the window.
MIL-188-110-16Tone, (MIL-188-110A/B Appendix B)
MIL-188-110-16Tone is a non-mandatory part of the MIL-STD-188-110 military standard for use by all
departments and agencies of the Department of Defense.
Parameter Value
Frequency range HF
Operation modes Simplex
Modulation 16 tone DPSK
Doppler Tone: 605 Hz, Freq1: 935 Hz, ... Freq16: 2585 Hz. Shift 110 Hz,
Symbol rate 75 Bd
Center frequency 1760 Hz
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
BINARY, HEX and ASCII output are provided.