Garmin GPS 18 Technical Specifications

Also see for GPS 18 5Hz: Reference guide Features Setup guide

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Garmin GPS 18 Technical Specifications Manual pdf 22 page image

GPS 18 Technical Specifications (190-00307-00) Rev. DPage 164.2.2 Transmitted TimeThe GPS sensor outputs UTC (Coordinated Universal Time) date and time of day in the transmittedsentences. Before the initial position fix, the on-board clock provides the date and time of day. After theinitial position fix, the date and time of day are calculated using GPS satellite information and aresynchronized with the measurement pulse output.The GPS 18-5Hz outputs a UTC with a tenths-of-a-second precision: 123456.8, for example.The GPS sensor uses information obtained from the GPS satellites to add or delete UTC leap seconds andcorrect the transmitted date and time of day. The transmitted date and time of day for leap secondcorrection follow the guidelines in “National Institute of Standards and Technology Special Publication432 (Revised 1990)” (for sale by the Superintendent of Documents, U.S. Government Printing Office,Washington, D.C., 20402, U.S.A.).When a positive leap second is required, one second is inserted at the beginning of the first hour (0h 0m 0s)of the day that the positive leap is occurring. The minute containing the leap second is 61 seconds long. TheGPS sensor would have transmitted this information for the leap second added December 31, 1998 asfollows:$GPRMC,235959,A,3851.3651,N,09447.9382,W,000.0,221.9,071103,003.3,E*69$GPRMC,000000,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*67$GPRMC,000000,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*67$GPRMC,000001,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*66If a negative leap second should be required, one second will be deleted at the end of some UTC month.The minute containing the leap second will be only 59 seconds long. In this case, the GPS sensor will nottransmit the time of day 0h 0m 0s (the “zero” second) for the day from which the leap second is removed.$GPRMC,235959,A,3851.3650,N,09447.9373,W,000.0,000.0,111103,003.3,E*69$GPRMC,000001,A,3851.3650,N,09447.9373,W,000.0,000.0,121103,003.3,E*6A$GPRMC,000002,A,3851.3650,N,09447.9373,W,000.0,000.0,121103,003.3,E*694.2.3 Global Positioning System Almanac Data (ALM)Almanac sentences are not normally transmitted. Send the GPS sensor a $PGRMO,GPALM,1 command toinitiate almanac transmission. Upon receipt of this command, the GPS sensor will transmit availablealmanac information on GPALM sentences. During the transmission of almanac sentences, other NMEA0183 data output is suspended temporarily.$GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15>*hh can be found in Section 4.1.1 Almanac Information (ALM).