Wavecom W61PC V7.5.0 - Manual (Page 154)

144  Transmission Modes WAVECOM Decoder W61PC/LAN Manual V7.5
The polarity of the bit stream (upper sideband (USB) or lower sideband (LSB)) cannot automatically be
derived from the signal. Polarity may be manually selected by using the Polarity menu field. Polarity in-
version does not cause a loss of signal synchronization.
DUP-ARQ-2
DUP-ARQ-2 is a further development of the DUP-ARQ system and the system characteristics are very simi-
lar. DUP-ARQ-2 allows transmission of ITA-2 (Baudot) or ITA-5 (ASCII) characters depending on the appli-
cation.
Parameter Value
Frequency range HF
Operation modes FSK, Duplex ARQ
Modulation FSK
Symbol rate 250.0 Bd
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info ITA-5 with block coding
DUP-ARQ-2 operates at a Symbol rate of 250 Baud on the radio link. A complete transmission cycle is 176
bits (704 ms). Both stations alternate in transmitting data blocks of 64 bits each.
The data format is 2 data blocks of 32 bits each. The blocks correspond to the DUP-ARQ (ARTRAC) sys-
tem. Each of the two blocks contains a 5 bit checksum (inverted Hamming) for error detection and a sin-
gle bit for the global parity (odd parity). Three 8 bit characters are transmitted in the data block. Two bits
remain unused and are set to zero.
Special blocks defining IDLE, INTERRUPT and other special functions are transmitted. For these blocks the
two normally unused bits specify the particular special functions with the combinations "10" or "11".
DUP-ARQ-2 has automatic channel selection facilities. Before transmission starts, the best available short-
wave transmission channel is selected and its quality is continuously checked for the duration of the
transmission. Within a given frequency range the system may select one of 5 possible channels which are
spaced at 400 Hz intervals. Because of this channel selection mechanism the linked stations may transmit
at different frequencies.
DUP-FEC-2
DUP-FEC-2 is a further development of the DUP-ARQ-2 system and the system characteristics are very
similar. DUP-FEC-2 allows transmission of ITA-2 (Baudot) or ITA-5 (ASCII) characters.
Parameter Value
Frequency range HF
Operation modes Broadcast/Duplex FEC
Modulation FSK
Symbol rate 125.0 and 250.0 Bd, variable 30-650 Bd