What is ALERT?

ALERT stands for Automated Local Evaluation in Real-Time.  It is a radio protocol developed by the NWS in the late 1970s for transmitting hydrometeorological data.  Some of the hallmarks of ALERT are:

  • 300 BAUD
  • Sensor IDs from 1 – 8192
  • Sensor values are integers from 0 to 2047
  • ALOHA transmissions – They speak when they have something to say and they don’t know if their data was received
  • More than one base station can receive transmissions
  • Transmission is four (4) bytes of data per transmission, with three (3) bytes of content and the rest of the bits are marker bits.
  • Data can be lost because two sites can transmit at the same time causing a collision
  • Rain count protocol is resilient, if we miss a transmission, we catch up with the total on the next transmission

This protocol is used widely in the U.S. and Australia.  In Australia, they call it ERRTS.

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