Spread-11, spread-21 and spread-51 – Wavecom W74PC V8.7.0 User Manual
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Transmission Modes
WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V8.7.0
For the FFT, bandwidths of 500 Hz, 1000 Hz, and 4000 Hz may be selected. A bandwidth of 500 Hz will
ensure a good quality of signal display, and will also enable a fine tuning of the signal. Then using the dis-
play cursors the center frequency of the signal may be determined. All 14 tones, except tone 2 and tone
13 are clearly displayed. The missing tones are the start and stop indicators which are of course only
transmitted at the start and the stop of the transmission. It is important to tune to the signal center fre-
quency as accurately as possible, because accuracy of this tuning directly influences the quality of demod-
ulation and the synchronization. In case the receiver AF output is used, the center frequency should be as
close to 409 Hz as possible. The value of the center frequency is directly transferred to the decoding soft-
ware module.
The screen shot below shows a decoded SP-14 signal.
SPREAD-11, SPREAD-21 and SPREAD-51
Like AUTOSPEC the SPREAD-11, SPREAD-21 and SPREAD-51 modes use the 10 bit Bauer code. For im-
proved reliability in terms of burst errors each character is spread in time (interleaving). After each bit of
the 10 bit Bauer code, 50 data bits (alternately 10 or 20) from other characters are sent. New characters
start at intervals of 10 bits.
Parameter
Value
Frequency range
HF
Operation modes
Simplex FEC
Modulation
FSK
Symbol rate
68.5-137 Bd, variable 30-650 Bd
Receiver settings
DATA, CW, LSB or USB
Input format(s)
AF, IF
Additional Info
10 Bit Bauer Code