the train synchronizing is necessary because the system needs to identify which rf burst from the hot transceiver 20 is the one the pll counter and event timer 34 needs to count cycles in and report when complete using the time stamp message 40 assume a sampling rate of every 2 4 seconds over the 2400 bps modulation signal there are 2400 possible rf states 1 0 transitions in non return to zero level per second which in a 2 4 second sampling window equals 5760 pulse states the hot and eot device both need to know which 1 out of the 5760 pulses is the reference set to measure transmit receipt time delays with during synchronizing the hot control unit 18 temporarily suspends normal hot eot message traffic and sends a 1 0 data pattern at 2400 bit sec to the eot device while time stamping each burst internally the eot device time stamps one of the received bursts with the time received and then transmits that back to the hot the hot computes an initial time difference value in the event that the time stamped reference set was not identified properly by the eot device on the first try there is a 1 out of 5760 chance the hot.