Garmin GPS 18x Series Technical Specifications

Also see for GPS 18x LVC: Declaration of conformity

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Garmin GPS 18x Series Technical Specifications Manual pdf 20 page image

190-00879-08 GPS 18x Technical Specifications Rev. BPage 164.2.2 Transmitted TimeThe GPS sensor outputs Coordinated Universal Time (UTC) date and time of day in the transmitted sentences.Before the initial position fix, the on-board clock provides the date and time of day. After the initial position fix, thedate and time of day are calculated using GPS satellite information and are synchronized with the measurementpulse output.The GPS 18x-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 and correct thetransmitted date and time of day. The transmitted date and time of day for leap second correction follow theguidelines in “National Institute of Standards and Technology Special Publication 432 (Revised 1990)” (for sale bythe 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 theday that the positive leap is occurring. The minute containing the leap second is 61 seconds long. The GPS sensorwould have transmitted this information for the leap second added December 31, 1998 as follows:$GPRMC,235959,A,3851.3651,N,09447.9382,W,000.0,221.9,071103,003.3,E*69$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 minutecontaining the leap second will be only 59 seconds long. In this case, the GPS sensor will not transmit the time ofday 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 $PGRMO,GPALM,1 command to initiatealmanac transmission. Upon receipt of this command, the GPS sensor will transmit available almanac informationon GPALM sentences. During the transmission of almanac sentences, other NMEA 0183 data output is suspendedtemporarily.$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).