SDM-300Ls Satellite Modem
Revision 1
Burst Mode Modulator Operation MN/SDM300L3.IOM
B–6
B.2.17 Transmit
Preamble
In burst mode, when RTS transitions from false to true, the modem shall turn on the RF
carrier and generate a burst preamble with the following characteristics:
96 symbols at 19.2 kbps
288 symbols at 57.6 kbps
CW
352 symbols
BIT TIMING
31 symbols
UNIQUE WORD
Channel contents:
CW:
I and Q channels contain all 1's
Bit
Timing:
I:
1010...
Q:
1010...
Unique Word: I:
000 0010 0011 1010 1001 0111 1001 1011
Q:
000 0010 0011 1010 1001 0111 1001 1011
*
Note:
Bit Timing and the Unique Word is BPSK and uncoded.
At the end of the preamble, the modulator shall cause CTS to transition from false to true.
This signals the baseband equipment to begin sending data. The RF carrier shall remain
on until RTS transitions back to false.
B.2.18 Transmit
Packet
The minimum length is 48 bps. The maximum length can be infinite. Packet length is
determined by the user.
B.2.19 Transmit
Postamble
When RTS transitions back to false, the modulator flushes the Encoder and sends the End
of Message pattern, turns off the RF carrier and resets CTS back to false. The EOM
pattern is shown below.
6 symbols
Flush
31 symbols
Unique Word’
31 symbols
Unique Word’
Unique Word Prime
I:
110 1100 1111 0100 1010 1110 0010 0000
Q:
110 1100 1111 0100 1010 1110 0010 0000
*Note:
The Unique Word Prime is BPSK and uncoded.
