Wavecom W61PC V7.5.0 - Manual (Page 186)

176  Transmission Modes WAVECOM Decoder W61PC/LAN Manual V7.5
Parameter Value
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info Async FSK only
For MIL-M-55529A mode standard baud rates from 50 to 110 Bd are available. Non-standard baud rates
may be selected using the Baudrate menu item.
From Options | Alphabet… you can select from different ITA-2 and ITA5 alphabets.
MIL-M-55529A is also known as MD-522 / GRC.
The center frequency of the decoder should be set to 1800 Hz when the receiver is correctly tuned to the
sending station. Small frequency variations are automatically compensated in the decoder.
The center frequency of the decoder can be adjusted by ± 400 Hz from its normal setting. By reading the
bar graph, any remaining frequency difference can be compensated by fine-tuning of the receiver frequen-
cy or by adjusting the center frequency of the decoder.
MOBITEX-1200
Mobitex 1200 is a multiple access packet radio system for wireless communications. Mobitex 1200 oper-
ates in the VHF band 76 – 82 MHz in Sweden and around 160 MHz in Finland, using 1200 bps FFSK indi-
rect FM. In Sweden a nationwide system channel is operating on 76.7375 MHz for base-to-mobile commu-
nications and on 81.7375 MHz in the opposite direction.
Parameter Value
Frequency range VHF
Operation modes Slotted Aloha TDMA system, full-duplex
Modulation FM, SUB FFSK
Symbol rate 1200 Bd
Center frequency 1500 Hz
Shift 600 Hz
Receiver settings Narrow FM, BW = 15 kHz
Input AF, IF
When traffic is low it is transmitted on the system channel, but if it is heavy the base stations may auto-
matically set up additional traffic channels or local system channels.
The Mobitex 1200 frames consist of a frame header with a unique synchronization word, base station
identification, traffic area identification and control flags followed by zero or more blocks of data, max 32
blocks. Each block consists of 6 bytes followed by an error correcting code.
Each system is identified by the unique 4 hexadecimal digit sync word. The sync word is inverted for mo-
bile-base communication.
The first data block – the link header - contains addressing information, frame type id, sequence number,
number of blocks in the frame and other control information. Frames can either be data link frames used
for the management of traffic or payload data frames called MRM frames. The payload frames contain so
called MPAKs, i.e. Mobitex packets which can have a total length of 512 bits. If the message is longer it is
split into a number of sequences.
The first payload data block contains MPAK header information: source and destination addresses, sub-
scription flags, packet class and packet type information and a timestamp if they are transmitted in the
base-to-mobile direction. The remote terminals do not insert a time stamp, this is done by the network.
The system has four payload packet classes, PSUBCOM for subscriber packet switched communication,
PSOSCOM for alert messaging, CSUBCOM for circuit-switched subscriber communication, and DTESERV for
service messages.