Garmin GPS 18 010-00321-56 User Manual

GPS 18 Technical Specifications (190-00307-00)

Rev. D

Page 20

NOTE: The GPS 18 products do not support PGRMB at this time. 

$PGRMB,<1>,<2>,<3>,<4>,<5>,K,<6>,<7>,<8>*hh<CR><LF>

<1>

Beacon tune frequency, 0.0, 283.5 to 325.0 kHz in 0.5 kHz steps

<2>

Beacon bit rate, 0, 25, 50, 100, or 200 bps

<3>

Beacon SNR, 0 to 31

<4>

Beacon data quality, 0 to 100

<5>

Distance to beacon reference station in kilometers

<6>

Beacon receiver communication status (0 = Check Wiring, 1 = No Signal, 2 = Tuning, 3 =
Receiving, 4= Scanning)

<7>

DGPS fix source (R = RTCM, W = WAAS, N = Non-DGPS Fix)

<8>

DGPS mode, A = Automatic, W = WAAS Only, R = RTCM Only, N = None (DGPS disabled)

Baud rate selection can be performed by sending the appropriate configuration sentence to the GPS sensor
as described in the $PGRMC Section 

, field <10>.

The highly accurate one-pulse-per-second (PPS) output is provided for applications requiring precise
timing measurements. After the initial position fix has been calculated, the PPS signal is generated and
continues until power down. The rising edge of the signal is aligned to the start of each GPS second within
1 

µs for all conditions in which the receiver has reported a valid and accurate position for at least the

previous 4 seconds.

The NMEA 0183 sentences that follow each rising edge of the PPS signal tell when you were and where
you were at that previous rising edge of the PPS signal, beginning with the GPRMC sentence as the lead
sentence in any particular NMEA 0183 record.

Regardless of the selected baud rate, the information transmitted by the GPS 18 series products is
referenced to the pulse immediately preceding the NMEA 0183 RMC sentence.

The accuracy of the one-pulse-per-second output is maintained only while the GPS receiver is computing a
valid position fix. To obtain the most accurate results, the one-pulse-per-second output should be calibrated
against a local time reference to compensate for cable and internal receiver delays and the local time bias.

The default pulse width is 100 ms, however; it may be programmed in 20 ms increments between 20 ms
and 980 ms as described in $PGRMC Section 

, field <13>.

The highly accurate five-pulse-per-second output is provided for applications requiring precise timing
measurements. After the initial position fix has been calculated, the GPS 18-5Hz generates the pulse signal,
which continues until power down. The rising edge of the signal is aligned to the start of each GPS second
within 1 

µs for all conditions in which the receiver has reported a valid and accurate position for at least the

previous 4 seconds.

The NMEA 0183 sentences that follow each rising edge of the Measurement Pulse Output signal tell when
and where you were at that previous rising edge of the Measurement Pulse Output signal, beginning with
the GPRMC sentence as the lead sentence in any particular NMEA 0183 record.

Regardless of the selected baud rate, the information transmitted by the GPS 18-5Hz is referenced to the
preceding five times per-second output pulse.

The accuracy of the five-pulse-per-second output is maintained only while the GPS 18-5Hz can compute a
valid position fix. To obtain the most accurate results, the five-pulse-per-second output should be calibrated
against a local time reference to compensate for cable and internal receiver delays and the local time bias.