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Hermes Operator Note Page 21 of 32
4.17 Over-Air Symbol Rate (AT S163)
Note: engineering function only.
This command sets the over-air baud rate to enable the modem to be used
with different radios and channel spacings. The command format is:
AT S163=n<CR><LF>
Where: n = 2 4800 symbols/sec
n = 3 9600 symbols/sec
Default: n = 2 4800 for 12.5kHz radios
n = 3 for 25kHz radios
Read AT S163?<CR><LF>
Read Return: n<CR><LF>
Example: AT S163=3<CR><LF> sets 9600 symbols/sec
4.18 Preamble Period (AT S165)
Note: engineering function only.
This command enables the number of preamble blocks (each block equals 6
bytes) that are transmitted before each data packet to be changed. This
preamble allows for the rise time of the transmitter as well as the minimum
number of blocks required by the receiver. This allows the system
performance to be changed to enable the modem to be used with different
transceiver equipment. The command format is as follows:
AT S165=n<CR><LF>
Where: n = 1 - 10 blocks
Default: n = 2
Read AT S165?<CR><LF>
Read Return: nn<CR><LF>
Example: AT S165=10<CR><LF> sets a preamble of 11 blocks
Note that a symbol period depends on the RF baud rate (as set by paragraph
4.17).
For the G-MAX radio at 9600 symbols per second n = 2.
For the SXn50 radio at 19200 symbols per second n = 14.