User's Manual

Company Confidential 29 Raveon Technologies Corp.
than 80% full. When it is asserted and it is “Clear to Send”, the buffers are
less than 80% full.
Packet Size
The over-the-air packet size may be set with the ATTT xx command. Once
the modem receives one full packet of data into via the serial port, it will
automatically key the transmitter and send the data. Factory default is 80
bytes.
Key-On_Data
When serial data is entering the StingRay’s RS-232 port, the StingRay looks
for pauses in the data as indication that it is time to send a packet of data
over the air. The factory default duration of the pause it looks for is 20mS, but
the user may change this to over values using the ATR3 xxx command,
where xxx is in milliseconds.
Busy-Channel Lock Out
If your system operation require the StingRay modem to monitor-before-
transmit, of if you do not want the StingRay to transmit on a channel that is
busy, you can enable “Busy-Channel-Lockout”, using the ATBC 1 command.
ATBC 0 disables BCL, and thus the modem will transmit whenever it has data
to send out. The factory-default is BCL disabled. Use caution when enabling
it, as a CW interferer, PC with poor shielding, or some other source of RF can
stop the modem from transmitting. The threshold where the StingRay senses
RF carrier, and determines that the channel is busy is set by the ATRA
command. This is factory calibrated to an equivalent RF level of
approximately -110dBm.
6.4. Data Reception
When the modem receives data over the radio, it checks it for errors, and if it
is error-free, it will send it out the serial port. Again, the serial port may be set
to any baud rate the user wishes, and the radio receiver and transmitter will
continue to operate independently of the baud rate.
When the modem receives a signal, it will assert the CD hardware signal on
the RS-232 serial port if it was configured to do so.
In general, the slower the over-the-air data rate, the easier it is for the modem
to receive the signal, and thus the more communication range the radio will
have. StingRay modems have a unique switched-filter along with digital
signal processing, that gives them more range a lower data rates. See
Section 10.1 Setting the Over-The-Air Data Rate for more information about
choosing the over-the-air data rate.