DGPS 53

integrated GPS/DGPS receiver
owners manual and reference guide

DGPS53Cover.p65

8/29/00, 11:10 AM
2000 GARMIN Corporation GARMIN International, Inc. 1200 East 151st Street, Olathe, Kansas 66062, U.S.A. Tel. 913/397.8200 or 800/800.1020 Fax 913/397.8282 GARMIN (Europe) Ltd. Unit 5, The Quadrangle, Abbey Park Industrial Estate, Romsey, SO51 9AQ, U.K. Tel. 44/1794.519944 Fax 44/1794.519222 GARMIN (Asia) Corporation No. 68, Jangshu 2nd Rd., Shijr, Taipei County, Taiwan Tel. 886/02.2642.8999 Fax 886/02.2642.9099 All rights reserved. Except as expressly provided herein, no part of this manual may be reproduced, copied, transmitted, disseminated, downloaded or stored in any storage medium, for any purpose without prior written consent of GARMIN Corporation. GARMIN Corporation hereby grants permission to download a single copy of this manual onto a hard drive or other electronic storage medium to be viewed for personal use, provided that such electronic or printed copy of this manual contains the complete text of this copyright notice and provided further that any unauthorized commercial distribution of this manual is strictly prohibited. Information in this manual is subject to change without notice. GARMIN Corporation reserves the right to change or improve its products and to make changes in the content without obligation to notify any person or organization of such changes. Visit the GARMIN website for current updates and supplemental information concerning the use and operation of this and other GARMIN products. Website address: www.garmin.com GARMIN and DGPS 53 are registered trademarks of GARMIN Corporation and may not be used without the express permission of GARMIN Corporation.

September 2000

Part Number 190-00194-00 Rev. A

Printed in Taiwan

Introduction
GARMIN Corporation warrants this product to be free from defects in materials and workmanship for one year from the date of purchase. GARMIN will, at its sole option, repair or replace any components that fail in normal use. Such repairs or replacement will be made at no charge to the customer for parts or labor. The customer is, however, responsible for any transportation costs. This warranty does not cover failures due to abuse, misuse, accident or unauthorized alteration or repairs. THE WARRANTIES AND REMEDIES CONTAINED HEREIN ARE EXCLUSIVE AND IN LIEU OF ALL OTHER WARRANTIES EXPRESS OR IMPLIED OR STATUTORY, INCLUDING ANY LIABILITY ARISING UNDER ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, STATUTORY OR OTHERWISE. THIS WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS, WHICH MAY VARY FROM STATE TO STATE. IN NO EVENT SHALL GARMIN BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES, WHETHER RESULTING FROM THE USE, MISUSE, OR INABILITY TO USE THIS PRODUCT OR FROM DEFECTS IN THE PRODUCT. SOME STATES DO NOT ALLOW THE EXCLUSION OF INCIDENTAL OR CONSEQUENTIAL DAMAGES, SO THE ABOVE LIMITATIONS MAY NOT APPLY TO YOU. To obtain warranty service, contact your GARMIN dealer or call the GARMIN Customer Service department (913-397-8200) for a returned merchandise tracking number. The unit should be securely packaged with the tracking number clearly marked on the outside of the package and sent freight prepaid and insured to a GARMIN warranty service station. A copy of the original sales receipt is required as the proof of purchase for warranty repairs. GARMIN retains the exclusive right to repair or replace the unit or software or offer a full refund of the purchase price at its sole discretion. SUCH REMEDY SHALL BE YOUR SOLE AND EXCLUSIVE REMEDY FOR ANY BREACH OF WARRANTY.

Limited Warranty

The GARMIN DGPS 53 has no user-serviceable parts. Should you ever encounter a problem with your receiver, please contact your GARMIN dealer or the GARMIN Customer Service department (913-397-8200 or 800-800-1020) for repairs. Any attempt to open the case to change or modify the unit in any way will void your warranty and may result in permanent damage to the equipment.

Introduction Cautions

All differential beacon receivers decode correction data determined at the beacon transmitter site via a GPS receiver(s). The GPS system is operated by the government of the United States which is solely responsible for their accuracy and maintenance. The DGPS beacon transmitters are operated by the U.S. Coast Guard (or similar government agency in other countries) which is responsible for their accuracy and maintenance. The Global Positioning System and the Differential Global Positioning System are under development and are subject to changes which could affect accuracy and performance of all GPS/DGPS equipment. Although a GPS/DGPS system is a precision electronic NAVigation AID (NAVAID), any NAVAID can be misused or misinterpreted, and therefore become unsafe. Use the GPS/ DGPS system at your own risk. To reduce this risk, carefully review and understand all aspects of this Owners Manual and carefully compare indications from your display to all available navigation sources including the information from other NAVAIDs, visual sightings, charts, etc. For safety, always resolve any discrepancies before continuing navigation. NOTE: This device complies with Part 15 of the FCC rules. Operation of this device is subject to the following conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

Introduction Table of Contents
Introduction Limited Warranty...1 Cautions...2 Table of Contents..3 Product Registration..4 Overview Capabilities & Package Contents..5 Installation Mounting the DGPS 53..6-7 Connecting DGPS 53.8-9 Operation Using the DGPS 53..10 NMEA Sentences..11-18 One-Pulse-Per-Second Output..18 Reference GPS: How It Works..19 DGPS: How It Works.20 Sources of Error..21-22 Troubleshooting Chart..23 DGPS 53 Specifications..24 Appendix A: Earth Datums..25-27 Index...28
Customer Service Product Registration

Product Registration

Help us better support you by completing our on-line registration today! Have the serial number of your DGPS 53 handy and connect to our website (www.garmin.com). Look for the Product Registration link on the Home page. If you have previously registered a GARMIN product purchase using a mail-in registration card, we invite you to reregister using our NEW on-line system. Many services provided by our new product registration system are now being automated and reregistering your purchase ensures you the best possible support from GARMIN.
Why should you register your GARMIN GPS unit? Notification of Product Updates Notification of New Products Lost or Stolen unit tracking

Serial Number

Use this area to record the serial number (8-digit number located on the bottom of the unit) in case it is lost, stolen, or needs service. Be sure to keep your original sales receipt in a safe place or attach a photocopy inside the manual. Serial Number:
The GARMIN DGPS 53 has no userserviceable parts. Should you ever encounter a problem with your unit, please contact your GARMIN dealer or GARMIN Customer Service (913-397-8200 or 800-800-1020) for repairs.
Repairs should only be made by an authorized GARMIN service center. Unauthorized repairs or modifications could void your warranty and authority to operate this device under FCC Part 15 regulations. See page 1 of this manual for further service details.

Overview

Capabilities
The DGPS 53 offers a host of powerful capabilities for enhanced performance and accuracy: Performance 12-channel GPS receiver tracks and uses up to 12 satellites for fast, accurate positioning. Single channel DGPS receiver has high-sensitivity automatic and manual tuning throughout the beacon broadcast band. Ease of Use Once installed, unit will automatically transmit navigation data. Convenience May be remotely mounted in an out-of-the-way location. Receiver status information is displayed directly on the chartplotter or PC. Low Power Consumption Draws approximately 170 milliamps during normal operation. Accuracy 1-5 (2DRMS) meters (typical).

Package Contents

Capabilities & Package Contents
Your GARMIN DGPS 53 package includes: DGPS 53 unit 30 Power/Data Cable Owners Manual & Reference Guide Beacon Reference Card If any parts are missing or damaged, please contact your GARMIN dealer immediately.

Installation

Mounting the Receiver

Mounting the DGPS 53

Note: As a general rule, mount the receiver at least three feet from all other antennas and the vessels electrical system components (alternator/ignition system).
Please read through these instructions thoroughly before attempting installation. Make sure you completely understand these instructions before you begin. When in doubt, seek professional assistance. The following additional items are needed or optional to complete the installation of your DGPS 53: Antenna mount Since antenna mounting locations and methods vary, you will need to obtain an antenna mount to install the DGPS 53. The receiver base fits a standard 1-inch, 14 threads-perinch mount. Check with your GARMIN dealer or a marine supply retailer for this item. On/Off switch (optional) Power to the receiver may be controlled by an on/off switch, such as an accessory switch on the control console. Check with your GARMIN dealer or a marine/ electric supply retailer for this item. GARMIN 60 Power/Data Cable for cable installation lengths greater than 30. Part number 010-10284-00 It is recommended that the system be temporarily hooked up with the wiring and the unit placed at the desired installation location. Then, check operation with potential interfering equipment turned on and off. (For example, other electronic equipment, fan motors, engine ignition, alternators, generators, radars and VHF radio transmissions can be sources of interference.) Position the receiver so that the clearest possible view of the sky and horizon in all directions is obtained. Avoid mounting the antenna next to large areas of conductive material (metal, aluminum, etc.) as this may cause poor signal reception. The DGPS 53 is supplied with a 30 feet power/data cable. When routing the wiring to the DGPS 53, avoid routing the cable near the vessels alternator or ignition system components or parallel to other power lines.

DB9 Female Serial Connector
DB25 Female Serial Connector
Some non-GARMIN devices may have a separate data line labeled RETURN, DATA GROUND or DATA -. If one of these lines exist, connect the BLACK wire from the power/data cable to it.

(-) (+)

Fuse 2-6A

Chartplotter

GROUND DATA OUT DATA IN

8-35VDC

Power/Data Cable & Chartplotter Connection
(1) RED: 8-35 VDC (2) BLACK: GROUND (5) WHITE: REMOTE ON/OFF* (4) BROWN: DATA IN (3) BLUE: DATA OUT (6) GREEN: DGPS STATUS LED (7) YELLOW : PPS

Power/Data Cable

Figure 3: Wiring a Chartplotter To the DGPS 53
Power/Data Cable & DB-9 Serial Connection
(1) RED: 8-35 VDC PIN 5: GROUND (2) BLACK: GROUND (5) WHITE: REMOTE ON/OFF* (4) BROWN: DATA IN (3) BLUE: DATA OUT (6) GREEN: DGPS STATUS LED (7) YELLOW : PPS
PIN 3: DATA OUT PIN 2: DATA IN

Serial Connector

Figure 4: Wiring a DB9 Serial Connector To the DGPS 53
Power/Data Cable Remote Power Switch

8-35 VDC

(1) RED: 8-35 VDC (2) BLACK: GROUND Closed- ON Open- OFF (5) WHITE: REMOTE ON/OFF*

Switch

Figure 5: Wiring a Remote Power Switch For the DGPS 53

Operation

First Time Fix

Using the DGPS 53

Once the DGPS is installed and powered on, it will begin to search for satellites and a DGPS beacon signal. Initially, it may take longer than normal to scan through the DGPS beacon frequencies. The DGPS 53 will output corrected navigation data once it has calculated an initial position fix and sucessfully received a DGPS signal. The following data will be output in NMEA 0183, Version 2.0 format:
Latitude/Longitude/Altitude Velocity Date/Time Error Estimates Satellite and Receiver Status DGPS Beacon Information

Auto-Tuning

Without external commands, the DGPS 53 will automatically scan frequencies between 283.5-325.0 kHz @ 0.5kHz steps for 100 and 200 bps stations only. To use 25 & 50 bps, you will need to manually tune the DGPS 53 (pg.13) via the chartplotter, PC or other compatible source. The DGPS 53 should tune into a DGPS station within about 10 minutes. The unit will store the last used frequency in non-volatile memory and default to that frequency on next use. If you lose DGPS signal, the unit will attempt to reconnect to the last frequency and if necessary, tune to another station.

Interfaces

The DGPS 53 interface protocol design is based on the National Marine Electronics Associations (NMEA) 0183 ASCII interface specification, which is fully defined in NMEA 0183, Version 2.0 and the Radio Technical Commission for Maritime Services RTCM Recommended Standards For Differential Navstar GPS Service, Version 2.1, RTCM Special Committee No. 104. Contact information to obtain copies of these specifications may be found on page 24. The DGPS 53 interface protocol also transmits additional information using the convention of GARMIN proprietary sentences ($PGxxx).

All configuration changes take effect after receipt of a valid value except baud rate and PPS mode. Baud rate and PPS mode changes take effect on the next power cycle.
Output Sentence Enable/Disable (PGRMO) The $PGRMO sentence provides the ability to enable and disable specific output sentences. The following sentences are enabled at the factory: GPGGA, GPGSA, GPGSV, GPRMC, and PGRMT. $PGRMO,<1>,<2>*hh<CR><LF> <1> Target sentence description (e.g., PGRMT, GPGSV, etc.) <2> Target sentence mode, where: 0 = disable specified sentence 1 = enable specified sentence 2 = disable all output sentences 3 = enable all output sentences (except GPALM) The following notes apply to the PGRMO input sentence: 1) If the target sentence mode is 2 (disable all) or 3 (enable all), the target sentence description is not checked for validity. In this case, an empty field is allowed (e.g., $PGRMO,,3), or the mode field may contain from 1 to 5 characters. 2) If the target sentence mode is 0 (disable) or 1 (enable), the target sentence description field must be an identifier for one of the sentences being output by the DGPS 53. 3) If either the target sentence mode field or the target sentence description field is not valid, the PGRMO sentence will have no effect. 4) $PGRMO,GPALM,1 will cause the sensor board to transmit all stored almanac information. All other NMEA sentence transmission will be temporarily suspended. Tune DGPS Beacon Receiver (PSLIB) The $PSLIB sentence provides the ability to manually tune the DGPS 53. $PSLIB,<1>,<2>*hh<CR><LF> <1> Beacon tune frequency, 0.0, 283.5 325.0 kHz in 0.5 kHz steps <2> Beacon bit rate, 0, 25, 50, 100, or 200 bps If valid data is received, the DGPS 53 will store it in the EEPROM and echo the PSLIB command to the beacon receiver. At power up or external reset, any stored frequency other than 0.0 causes the DGPS 53 to automatically tune.
NMEA Transmitted Sentences
This section defines the sentences which can be output by the DGPS 53. (GPALM, GPGGA, GPGSA, GPGSV, GPRMC, GPVTG, PGRME, PGRMT, PGRMV, PGRMF, LCGLL, LCVTG) Sentence Transmission Rate Sentences are transmitted with respect to the user selected baud rate. Regardless of the selected baud rate, the information transmitted by the DGPS 53 is referenced to the one-pulse-per-second output pulse immediately preceding the GPRMC sentence. The maximum number of fields allowed in a single sentence is 82 characters including delimiters. Values in the table include the sentence start delimiter character $ and the termination delimiter <CR><LF>. The factory set defaults will result in a once per second transmission at the NMEA specification transmission rate of 4800 baud. Transmitted Time The DGPS 53 outputs UTC (Coordinated Universal Time) date and time of day in the transmitted sentences. Prior to the initial position fix, the date and time of day are provided by the on-board clock. After the initial position fix, the date and time of day are calculated using GPS satellite information and are synchronized with the one-pulse-persecond output. The DGPS 53 uses information obtained from the GPS satellites to add or delete UTC leap seconds and correct the transmitted date and time of day.

Global Positioning System Almanac Data (ALM) $GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15> *hh<CR><LF> Almanac sentences are not normally transmitted. Almanac transmission can be initiated by sending the sensor board a $PGRMO,GPALM,1 command. Upon receipt of this command the sensor board will transmit available almanac information on GPALM sentences. During the transmission of almanac sentences other NMEA data output will be temporarily suspended. Reference the Alamanac (ALM) sentence on page 11 for <field information>.
Global Positioning System Fix Data (GGA) $GPGGA,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,M,<10>,M,<11>,<12>*hh<CR><LF> Using the <1> UTC time of position fix, hhmmss format DGPS 53 <2> Latitude, ddmm.mmmm format (leading zeros will be transmitted) <3> Latitude hemisphere, N or S <4> Longitude, dddmm.mmmm format (leading zeros will be transmitted) <5> Longitude hemisphere, E or W <6> GPS quality indication, 0 = fix not available, 1 = Non-differential GPS fix available, 2 = Differential GPS (DGPS) fix available, 6 = Estimated <7> Number of satellites in use, 00 to 12 (leading zeros will be transmitted) <8> Horizontal dilution of precision, 0.5 to 99.9 <9> Antenna height above/below mean sea level, -9999.9 to 99999.9 meters <10> Geoidal height, -999.9 to 9999.9 meters <11> Differential GPS (RTCM SC-104) data age, number of seconds since last valid RTCM transmission (null if non-DGPS) <12> Differential Reference Station ID, 0000 to 1023 (leading zeros will be transmitted, null if nonDGPS) GPS DOP and Active Satellites (GSA) $GPGSA,<1>,<2>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<4>,<5>,<6> *hh<CR><LF> <1> Mode, M = manual, A = automatic <2> Fix type, 1 = not available, 2 = 2D, 3 = 3D <3> PRN number, 01 to 32, of satellite used in solution, up to 12 transmitted (leading zeros will be transmitted) <4> Position dilution of precision, 0.5 to 99.9 <5> Horizontal dilution of precision, 0.5 to 99.9 <6> Vertical dilution of precision, 0.5 to 99.9 GPS Satellites in View (GSV) $GPGSV,<1>,<2>,<3>,<4>,<5>,<6>,<7>,.<4>,<5>,<6>,<7>*hh<CR><LF> <1> Total number of GSV sentences to be transmitted <2> Number of current GSV sentence <3> Total number of satellites in view, 00 to 12 (leading zeros will be transmitted) <4> Satellite PRN number, 01 to 32 (leading zeros will be transmitted) <5> Satellite elevation, 00 to 90 degrees (leading zeros will be transmitted) <6> Satellite azimuth, 000 to 359 degrees, true (leading zeros will be transmitted) <7> Signal to noise ratio (C/No) 00 to 99 dB, null when not tracking (leading zeros will be transmitted) NOTE: Items <4>,<5>,<6> and <7> repeat for each satellite in view to a maximum of four (4) satellites per sentence. Additional satellites in view information must be sent in subsequent sentences. These fields will be null if unused.

Recommended Minimum Specific GPS/TRANSIT Data (RMC) $GPRMC,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>*hh<CR><LF> <1> UTC time of position fix, hhmmss format <2> Status, A = Valid position, V = NAV receiver warning <3> Latitude, ddmm.mmmm format (leading zeros will be transmitted) <4> Latitude hemisphere, N or S <5> Longitude, dddmm.mmmm format (leading zeros will be transmitted) <6> Longitude hemisphere, E or W <7> Speed over ground, 000.0 to 999.9 knots (leading zeros will be transmitted) <8> Course over ground, 000.0 to 359.9 degrees, true (leading zeros will be transmitted) <9> UTC date of position fix, ddmmyy format <10> Magnetic variation, 000.0 to 180.0 degrees (leading zeros will be transmitted) <11> Magnetic variation direction, E or W (westerly variation adds to course over ground) <12> Mode indicator (only output if NMEA 2.30 active), A = Autonomous, D = Differential, E = Estimated, N = Data not valid Track Made Good and Ground Speed with GPS Talker ID (VTG) The GPVTG sentence reports track and velocity information with a checksum: $GPVTG,<1>,T,<2>,M,<3>,N,<4>,K,<5>*hh<CR><LF> <1> True course over ground, 000 to 359 degrees (leading zeros will be transmitted) <2> Magnetic course over ground, 000 to 359 degrees (leading zeros will be transmitted) <3> Speed over ground, 000.0 to 999.9 knots (leading zeros will be transmitted) <4> Speed over ground, 0000.0 to 1851.8 kilometers per hour (leading zeros will be transmitted) <5> Mode indicator (only output if NMEA 2.30 active), A = Autonomous, D = Differential, E = Estimated, N = Data not valid Geographic Position with LORAN Talker ID (LCGLL) The LCGLL sentence reports position information. $LCGLL,<1>,<2>,<3>,<4>,<5>,<6>,<7><CR><LF> <1> Latitude, ddmm.mmmm format (leading zeros will be transmitted) <2> Latitude hemisphere, N or S <3> Longitude, dddmm.mmmm format (leading zeros will be transmitted) <4> Longitude hemisphere, E or W <5> UTC time of position fix, hhmmss format <6> Status, A = Valid position, V = NAV receiver warning <7> Mode indicator (only output if NMEA 2.30 active), A = Autonomous, D = Differential, E = Estimated, N = Data not valid

Track Made Good and Ground Speed with LORAN Talker ID (LCVTG) Using the The LCVTG sentence reports track and velocity information. DGPS 53 $LCVTG,<1>,T,<2>,M,<3>,N,<4>,K,<5><CR><LF> <1> True course over ground, 000 to 359 degrees (leading zeros will be transmitted) <2> Magnetic course over ground, 000 to 359 degrees (leading zeros will be transmitted) <3> Speed over ground, 000.0 to 999.9 knots (leading zeros will be transmitted) <4> Speed over ground, 0000.0 to 1851.8 kilometers per hour (leading zeros will be transmitted) <5> Mode indicator (only output if NMEA 2.30 active), A = Autonomous, D = Differential, E = Estimated, N = Data not valid Estimated Error Information (PGRME) The GARMIN Proprietary sentence $PGRME reports estimated position error information. $PGRME,<1>,M,<2>,M,<3>,M*hh<CR><LF> <1> Estimated horizontal position error (HPE), 0.0 to 999.9 meters <2> Estimated vertical position error (VPE), 0.0 to 999.9 meters <3> Estimated position error (EPE), 0.0 to 999.9 meters GPS Fix Data Sentence (PGRMF) The sentence $PGRMF is GARMIN Proprietary format; reporting time, position, speed and course information $PGRMF,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15> *hh<CR><LF> <1> GPS week number (0 - 1023) <2> GPS seconds (0 - 604799) <3> UTC date of position fix, ddmmyy format <4> UTC time of position fix, hhmmss format <5> GPS leap second count <6> Latitude, ddmm.mmmm format (leading zeros will be transmitted) <7> Latitude hemisphere, N or S <8> Longitude, dddmm.mmmm format (leading zeros will be transmitted) <9> Longitude hemisphere, E or W <10> Mode, M = manual, A = automatic <11> Fix type, 0 = no fix, 1 = 2D fix, 2 = 3D fix <12> Speed over ground, 0 to 1851 kilometers/hour <13> Course over ground, 0 to 359 degrees, true <14> Position dilution of precision, 0 to 9 (rounded to nearest integer value) <15> Time dilution of precision, 0 to 9 (rounded to nearest integer value) Sensor Status Information (PGRMT) The GARMIN Proprietary sentence $PGRMT gives information concerning the status of the DGPS 53. This sentence is transmitted once per minute regardless of the selected baud rate.

$PGRMT,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>*hh<CR><LF> <1> Product, model and software version <2> ROM checksum test, P = pass, F = fail <3> Receiver failure discrete, P = pass, F = fail <4> Stored data lost, R = retained, L = lost <5> Real time clock lost, R = retained, L = lost <6> Oscillator drift discrete, P = pass, F = excessive drift detected <7> Data collection discrete, C = collecting, null if not collecting <8> Board temperature in degrees C <9> Board configuration data, R = retained, L = lost 3D velocity Information (PGRMV) The GARMIN Proprietary sentence $PGRMV reports three-dimensional velocity information. $PGRMV,<1>,<2>,<3>*hh<CR><LF> <1> True east velocity, -514.4 to 514.4 meters/second <2> True north velocity, -514.4 to 514.4 meters/second <3> Up velocity, -999.9 to 9999.9 meters/second DGPS Beacon Information (PGRMB) The GARMIN proprietary sentence $PGRMB reports DGPS beacon information. $PGRMB,<1>,<2>,<3>,<4>,<5>,K*<CR><LF> <1> Beacon tune frequency, 0.0, 283.5 325.0 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 One-Pulse-Per-Second Output The highly accurate (within 1ms) one-pulse-per-second (PPS) output is provided for applications requiring precise timing measurements. The signal is generated after the initial position fix has been calculated and continues until power down. The rising edge of the signal is synchronized to the start of each GPS second. Regardless of the selected baud rate, the information transmitted by the DGPS 53 is referenced to the pulse immediately preceding the NMEA 0183 RMC sentence. The accuracy of the PPS output is maintained only while the DGPS 53 can compute 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 msec, however; it may be programmed in 20 msec increments between 20 msec and 980 msec as described in $PGRMC on page 12.

Reference

GPS: How It Works
The global positioning system is a satellite-based navigation system consisting of a network of 24 orbiting satellites that are twelve thousand miles in space and in six different orbital paths. The satellites are constantly moving and you can receive satellite signals anywhere in the world, at any time. The GPS signal contains a pseudo-random code, ephemeris (pronounced: ee-fem-er-is) and almanac data. This code identifies which satellite is transmittingin other words, an I.D. code. We refer to satellites by their PRN (pseudo-random number), from 1 through 32. Ephemeris data is constantly transmitted by each satellite and contains important information such as status of the satellite, current date, and time. The almanac data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits almanac data showing the orbital information for that satellite and for every other satellite in the system. Each satellite transmits a message which essentially says, Im satellite #X, my position is currently Y, and this message was sent at time Z. Of course, this is a gross oversimplification, but you get the idea. The GPS receiver reads the message and saves the data for continual use. Now, to determine your position the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received by the GPS receiver. The time difference tells the GPS receiver how far away that particular satellite is. If we add distance measurements from a few more satellites, we can determine our position. This is what a GPS receiver does. With a minimum of three or more satellites, your GPS receiver can determine a latitude/longitude positionwhats called a 2D position fix. With four or more satellites, a GPS receiver can determine a 3D position which includes latitude, longitude, and altitude. By continuously updating your position, a GPS receiver can also accurately provide speed and direction of travel.

DGPS: How It Works

The DGPS 53 has the GPS and DGPS receivers combined within the same housing.
Differential GPS (DGPS) is a technique used to improve the accuracy of the Global Positioning System. DGPS reduces the effects of ionospheric variations and can improve position accuracy typically to 1-5 meters. The DGPS Beacon Transmitter is placed at a known location (i.e., the exact position of the site has been previously determined). At the beacon transmitter site, the GPS satellites are monitored using a GPS receiver. This receiver is equipped to calculate corrections for each satellite received. The correction is the difference between the distance to the satellite (from the beacon site) as measured by the GPS receiver, and the actual distance to the satellite based on the known location of the beacon site. These corrections are communicated to the DGPS 53 through the DGPS Beacon Station. The DGPS 53 then uses the corrections to remove errors from its own measurements. Satellites received by the DGPS 53, but not by the GPS receiver at the beacon transmitter site, will not have corresponding corrections. When four or more satellites received by the DGPS 53 have corresponding corrections, the result is a highly accurate position reading. The more satellites with corrections, the more accurate the position. The DGPS 53 receives RTCM SC-104 format signals from ground based DGPS Beacon Stations operating in the 283.5 kHz to 325.0 kHz frequency band and data rates of 25, 50, 100, or 200 bits per second. These stations are typically operated by government agencies such as the U.S. Coast Guard. Generally, the closest DGPS station will provide the most accurate correction data. Individual stations vary and the user may wish to verify the suitability of the signal for the intended application with the station operator. The station power is normally set to provide a usable range somewhere near 300 km. Other factors such as local interference, lightning, time of day and season, and if the path to the station is over ground or water, and antenna selection or installation affect the usable signal range.

Sources of Error

Using a DGPS Beacon Receiver with your existing GPS Receiver can provide substantial improvements in accuracy; however, there may be occasions when the best possible accuracy will not occur. Several factors can contribute to a degraded DGPS accuracy. Loss of DGPS Beacon Signal Obviously, the lack of DGPS correction data will result in reduced accuracy. Accuracy will be the same as if no beacon receiver was being used. Several conditions can cause a loss of the beacon signal: Poor data exchange between DGPS receiver and the GPS receiver can result in intermittent or nonexistent correction data. The range of a DGPS beacon transmitter (see the accompanying Beacon Reference Card) is typically a few hundred miles, or less. Beyond this range, the beacon signal cannot be reliably received. Interference to the beacon signal can be experienced during periods of thunderstorm activity. Other sources of interference, such as alternator motors, ignition systems and VHF, can also affect signal reception. Alternator/ignition interference can be minimized through proper shielding of the ships wiring, by using an EMI/RFI filter, and by mounting the beacon receivers antenna away from these sources of interference. Multipath Multipath error occurs when the GPS signal is reflected before it reaches the GPS receiver. The reflected signal takes slightly longer to reach the GPS receiver than a non-reflected signal. This added time delay results in position error. (The distance to each satellite is calculated based upon the time it takes the GPS signal to reach the GPS receiver.) Multipath error can be minimized by mounting the GPS antenna at a location which minimizes the potential for reflected signals. Generally, the GPS antenna should be mounted on a large, flat horizontal surface and away from any vertical structure (cabin walls, large mast, etc.) which could reflect the GPS signal.

Reference Sources of Error
Number of Satellites Visible As previously stated, the number of satellites available can affect position accuracy. To apply the corrections provided for the satellites received at the beacon transmitter station, the same satellites (at least in part) must be received by your GPS receiver. And, certainly, if there arent enough satellites to determine a GPS position, there arent enough satellites to calculate a DGPS position. Atmospheric Conditions Differences in the ionosphere and/or troposphere between the DGPS broadcast station and the DGPS receiver can result in decreased position accuracy. Although this does not cause significant error, the amount of error can increase as you get further away from the DGPS broadcast station. Satellite Geometry A minimum of 4 satellites are required to determine a 3D position. At times, additional satellites are required due to their placement with respect to each other. This relative placement is referred to as satellite geometry. Ideal satellite geometry exists when the satellites are located at wide angles with respect to each other. When satellites are located in a line or a close group, satellite geometry is considered poor. This same requirement applies to DGPS. If corrections are available for four different satellites, but they are all located in the same general area or in a line, the DGPS corrections will be minimal. However, if the same four satellites are placed farther apart, in several very different directions from our position, the corrections will have a much greater effect and the position accuracy will be greatly improved.
Reference Troubleshooting Chart
Problem Possible Cause 1) Beacon signal weak Interference from ships electrical system, thunderstorm or not received. activity, or another source is inhibiting signal lock on. Wrong frequency or bit rate selected. 2) Accuracy not as expected Poor satellite geometry exists or too few satellites are visible. Interference to GPS antenna and/or beacon antenna exists. Multipath signals being received by GPS unit. Too far from DGPS transmitter or not tuned to closest station. Unit not wired properly. Check wiring. Receiving device not properly configured.
3) No output from DGPS 53.

Physical

DGPS 53 Specifications
Size: Weight: Operating Range: Waterproof:
4.6W x 5.3H (117mm x 135mm) 23.9 ounces (0.678 kg) -68F to +158F (-20C to +70C) -1 meter submersion for 30 minutes IPX7 rating for IEC529
Mount Thread Size: 1 diameter at 14 threads/inch Power Voltage: 8 - 35 vDC using supplied power/data cable. Surge and reverse polarity protected for up to 80 vDC. 95 mA @ 12 vDc 283.5 - 325.0 kHz @ 0.5kHz 200/100/50/25 BPS All 200 & 100 BPS Channels 10 V MSK (Minimum Shift Keying) 25, 50, 100, 200 bps RS-232 or NMEA 0183, 4800 baud Binary (Magnavox), $PSLIB (Starlink) Output: Output Sentence: Pulse Per Second: RS-baud RTCM SC-104 (6 of 8 bit format) NMEA 0183 version 2.0 One-Pulse-Per-Second accuracy; 1 microsecond at rising edge of PPS pulse
Complete information concerning NMEA & RTCM formats and sentences is available for purchase at: National Marine Electronics Association (NMEA) PO Box 3435 New Bern, NC 28564-3435 USA 252-638-2626 252-638-4885 FAX. www.nmea.org Radio Technical Commission For Maritime Services (RTCM) 1800 Diagonal Road, Suite 600 Alexandria, VA 22314-2480, USA 703-684-4481 (Info Only) 703-836-4229 FAX www.rtcm.org
Current Drain: Signal Processing Frequency Range: Data Rates: Auto Tuning: Minimum Signal: Data Processing Demodulation: MSK Bit Rates: Interfaces Input: Input Sentences:

Appendix A Earth Datums

The following is a list of the GARMIN DGPS 53 earth datum indexes and the corresponding earth datum name (including the area of application):
32 ADINDAN - Ethiopia, Mali, Senegal, Sudan AFGOOYE - Somalia AIN EL ABD 1970 - Bahrain Island, Saudi Arabia ANNA 1 ASTRO 1965 - Cocos Island ARC 1950 - Botswana, Lesotho, Malawi, Swaziland, Zaire, Zambia, Zimbabwe ARC 1960 - Kenya, Tanzania ASCENSION ISLAND 1958 - Ascension Island ASTRO BEACON E - Iwo Jima Island AUSTRALIAN GEODETIC 1966 - Australia, Tasmania Island AUSTRALIAN GEODETIC 1984 - Australia, Tasmania Island ASTRO DOS 71/4 - St. Helena Island ASTRONOMIC STATION 1952 - Marcus Island ASTRO B4 SOROL ATOLL - Tern Island BELLEVUE (IGN) - Efate and Erromango Islands BERMUDA 1957 - Bermuda Islands BOGOTA OBSERVATORY - Colombia CAMPO INCHAUSPE - Argentina CANTON ASTRO 1966 - Phoenix Islands CAPE CANAVERAL - Florida, Bahama Islands CAPE - South Africa CARTHAGE - Tunisia CHATHAM 1971 - Chatham Island (New Zealand) CHUA ASTRO - Paraguay CORREGO ALEGRE - Brazil DJAKARTA (BATAVIA) - Sumatra Island (Indonesia) DOS 1968 - Gizo Island (New Georgia Islands) EASTER ISLAND 1967 - Easter Island EUROPEAN 1950 - Austria, Belgium, Denmark, Finland, France, Germany, Gibraltar, Greece, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland EUROPEAN 1979 - Austria, Finland, Netherlands, Norway, Spain, Sweden, Switzerland FINLAND HAYFORD 1910 - Finland GANDAJIKA BASE - Republic of Maldives GEODETIC DATUM 1949 - New Zealand ORDNANCE SURVEY OF GREAT BRITAIN 1936 - England, Isle of Man, Scotland, Shetland Islands, Wales

GUAM 1963 - Guam Island GUX 1 ASTRO - Guadalcanal Island HJORSEY 1955 - Iceland HONG KONG 1963 - Hong Kong INDIAN - Bangladesh, India, Nepal INDIAN - Thailand, Vietnam IRELAND 1965 - Ireland ISTS O73 ASTRO 1969 - Diego Garcia JOHNSTON ISLAND 1961 - Johnston Island KANDAWALA - Sri Lanka KERGUELEN ISLAND - Kerguelen Island KERTAU 1948 - West Malaysia, Singapore L.C. 5 ASTRO - Cayman Brac Island LIBERIA 1964 - Liberia LUZON - Mindanao Island LUZON - Phillippines (excluding Mindanao Island) MAHE 1971 - Mahe Island MARCO ASTRO - Salvage Islands MASSAWA - Eritrea (Ethiopia) MERCHICH - Morocco MIDWAY ASTRO 1961 - Midway Island MINNA - Nigeria NORTH AMERICAN 1927 - Alaska NORTH AMERICAN 1927 - Bahamas (excluding San Salvador Island) NORTH AMERICAN 1927 - Central America (Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua) NORTH AMERICAN 1927 - Canal Zone NORTH AMERICAN 1927 - Canada (including Newfoundland Island) NORTH AMERICAN 1927 - Caribbean (Barbados, Caicos Islands, Cuba, Dominican Republic, Grand Cayman, Jamaica, Leeward Islands, Turks Islands) NORTH AMERICAN 1927 - Mean Value (CONUS) NORTH AMERICAN 1927 - Cuba NORTH AMERICAN 1927 - Greenland (Hayes Peninsula) NORTH AMERICAN 1927 - Mexico NORTH AMERICAN 1927 - San Salvador Island NORTH AMERICAN 1983 - Alaska, Canada, Central America, CONUS, Mexico NAPARIMA, BWI - Trinidad and Tobago NAHRWAN - Masirah Island (Oman) NAHRWAN - Saudi Arabia NAHRWAN - United Arab Emirates
107 OBSERVATORIO 1966 - Corvo and Flores Islands (Azores) OLD EGYPTIAN - Egypt OLD HAWAIIAN - Mean Value OMAN - Oman PICO DE LAS NIEVES - Canary Islands PITCAIRN ASTRO 1967 - Pitcairn Island PUERTO RICO - Puerto Rico, Virgin Islands QATAR NATIONAL - Qatar QORNOQ - South Greenland REUNION - Mascarene Island ROME 1940 - Sardinia Island RT 90 - Sweden PROVISIONAL SOUTH AMERICAN 1956 - Bolivia, Chile, Colombia, Ecuador, Guyana, Peru, Venezuela SOUTH AMERICAN 1969 - Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Guyana, Paraguay, Peru, Venezuela, Trinidad and Tobago SOUTH ASIA - Singapore PROVISIONAL SOUTH CHILEAN 1963 - South Chile SANTO (DOS) - Espirito Santo Island SAO BRAZ - Sao Miguel, Santa Maria Islands (Azores) SAPPER HILL 1943 - East Falkland Island SCHWARZECK - Namibia SOUTHEAST BASE - Porto Santo and Madeira Islands SOUTHWEST BASE - Faial, Graciosa, Pico, Sao Jorge, and Terceira Islands (Azores) TIMBALAI 1948 - Brunei and East Malaysia (Sarawak and Sabah) TOKYO - Japan, Korea, Okinawa TRISTAN ASTRO 1968 - Tristan da Cunha User defined earth datum VITI LEVU 1916 - Viti Levu Island (Fiji Islands) WAKE-ENIWETOK 1960 - Marshall Islands WORLD GEODETIC SYSTEM 1972 WORLD GEODETIC SYSTEM 1984 ZANDERIJ - Surinam CH-1903 - Switzerland Hu - Tzu - Shan Indonesia 74 Austria Potsdam Taiwan (modified Hu-Tzu-Shan)