User Manual Part 2

CHAPTER 7
THEORY OF OPERATION
Revised: 9 Oct 03 7-3 EST P/N AA104
EFFECTIVE BAUD RATE
The maximum input baud rate to the modem is 19,200 baud, asynchronous, full duplex, but this is misleading since the ESTeems
actually communicate to each simplex over the RF link, at 19,200 bps (25 kHz channel spacing - Model 192C/F) or 9,600 bps (12.5
kHz channel spacing - Model 192C/F). The effective baud rate is a function of the above plus the packet length variable in the
ESTeem (definable from 1 to 2000 bytes). If the packlength variable is set to 2000 bytes the effective baud rate is approximately
18,000 baud (25 kHz channel spacing) or 9,000 baud (12.5 kHz channel spacing) the effective baud rate will degrade as the
packlength variable is reduced.
Another item that must be understood is transmission turn around time. Remember that the ESTeem sends a data packet and
waits for an (ACK) from the destination modem before another packet is transmitted. All radio transmitters have a fixed delay
time, this is the amount of time it takes the transmitter to stabilize once it is energized before it can send data. In the ESTeem the
delay is approximately 15 milliseconds one way which includes transmitter turn-on time and packet frame overhead or a total turn
around time accounting for the (ACK) of 30 milliseconds. Therefore total time to send a data packet is 30 milliseconds plus the
time required to send the data (i.e. number of bits sent/19,200 b/s).