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APCO Project 25 Conventional System While current Subscriber Two-Way Radios con- tain timers for measuring differences in time, there is no internal clock for keeping track of time of day.
Motorola Inc. January 1999
English (United States)
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MO7VROLA Technical Developments
PSEUDO-REAL TIME CLOCK FOR SUBSCRIBER TWO-WAY RADIOS
by John Cherney
APCO Project 25 Conventional System
While current Subscriber Two-Way Radios con- tain timers for measuring differences in time, there is no internal clock for keeping track of time of day.
Clock chips could be added to the radio, but these chips would take up valuable space in the hardware and require either a battery separate from the radio's battery, or use the radio's current battery. The first option would make it difficult for the radio user to change the battery when necessary, and the second option would force tire radio user to reset the time after every battery removal, or whenever the radio battery loses charge. The second option is also an increase on the battery dram.
There are some frames, (such as Low Speed Data Word) in the current digital voice signaling that are unused. The time of day could be placed in these unused frames and broadcast in every trans- mission.
The base stations have access to current time of day, either through the network or through devices attached to the base station.
The radio would listen on the channel, extract the time of day out of any transmitted message, and use its internal timers to keep track of the time of day in between transmissions. This would give the radio an estimate of current time of day, which could be used by the radio's features.