Garmin GPS 20A Manual

The Garmin GPS 20A is a high-sensitivity GPS sensor designed for marine and automotive applications, featuring NMEA 0183 output, WAAS/EGNOS capability, waterproof construction (IPX7), and fast time-to-first-fix. It provides reliable position, velocity, and time data for integration with chartplotters, autopilots, and other navigation systems. Below are key sections for safety, features, installation, configuration, operation, and troubleshooting.

Features at a Glance

Key components: GPS antenna/receiver unit, waterproof cable with connector, mounting hardware, status LED.

Feature	Description
High-sensitivity GPS receiver	Acquires and tracks satellites in challenging conditions
WAAS/EGNOS enabled	Provides improved position accuracy
NMEA 0183 output	Standard marine data protocol (4800 baud default)
IPX7 waterproof rating	Protected against immersion in 1 meter of water for 30 minutes
Fast Time-To-First-Fix (TTFF)	Typically under 45 seconds (hot start)
Status LED indicator	Shows power and satellite acquisition status
Compact design	Easy to mount in various locations
Wide operating voltage	6 to 40 VDC for marine and automotive use
Low power consumption	Typically 45 mA at 12 VDC
Built-in backup battery	Maintains satellite almanac for faster startup

Installation

Unpack and inspect contents. Select mounting location with clear view of sky.

1. Mounting: Use provided hardware to secure unit. Ensure mounting surface is clean and flat.
2. Power connection: Connect red wire to positive DC source (6-40V), black wire to negative/ground.
3. Data connection: Connect blue (TX/A) and brown (TX/B) wires to NMEA 0183 input of your device.
4. Shield connection: Connect bare shield wire to ground at device end for noise reduction.
5. Route cable: Secure cable away from moving parts and heat sources.

WARNING! Ensure power is off during installation. Do not mount near magnetic compasses (maintain at least 3 feet/1 meter distance).

First-Time Setup

Apply power; allow unit to acquire satellites.

1. Initial acquisition: After first power-up, unit may take several minutes to acquire satellites (cold start).
2. Status LED: Solid red = power on, no fix. Flashing green = acquiring satellites. Solid green = valid GPS fix.
3. Verify output: Connect to compatible NMEA 0183 device to confirm data reception.
4. Position verification: Compare GPS position with known location to verify accuracy.

CAUTION! Ensure proper polarity when connecting power wires. Reverse polarity may damage unit.

Specifications

• Receiver Type: 20-channel GPS with WAAS/EGNOS
• Update Rate: 1 Hz (1 update per second)
• Accuracy: Position: <3 meters 95% typical (with WAAS/EGNOS). Velocity: 0.1 knot RMS
• Acquisition Times: Hot start: <15 seconds. Warm start: <45 seconds. Cold start: <75 seconds
• Output Protocol: NMEA 0183 version 3.01 (default sentences: GGA, GLL, GSA, GSV, RMC, VTG, ZDA)
• Baud Rate: 4800 (fixed)
• Power Supply: 6 to 40 VDC, 45 mA typical at 12 VDC
• Backup Battery: 7-year lithium cell (non-replaceable)
• Waterproof Rating: IPX7 (submersible to 1 meter for 30 minutes)
• Operating Temperature: -15°C to 70°C (5°F to 158°F)
• Storage Temperature: -40°C to 85°C (-40°F to 185°F)
• Dimensions: 2.4" x 2.4" x 0.9" (61 x 61 x 23 mm)
• Cable Length: 15 feet (4.5 meters)

Controls and Connections

Unit has no physical controls. All operation is automatic once powered.

Cable Connections:

• Red: Power + (6-40 VDC)
• Black: Power - (Ground)
• Blue: NMEA 0183 TX/A (Data Out +)
• Brown: NMEA 0183 TX/B (Data Out -)
• Bare: Shield (Ground at device end only)

Status LED Indicators:

• Solid Red: Power on, searching for satellites
• Flashing Green: Acquiring satellites (no valid fix yet)
• Solid Green: GPS fix acquired, valid position data being output
• Off: No power or unit in sleep mode (if supported)

Connecting to Devices

Connect to NMEA 0183 compatible devices: chartplotters, autopilots, radar, AIS, etc.

1. Identify device NMEA input: Consult your device manual for NMEA 0183 input connections.
2. Wiring: Connect GPS 20A TX/A (blue) to device NMEA IN +. Connect GPS 20A TX/B (brown) to device NMEA IN -.
3. Shield: Connect bare shield wire to ground at device end (not at GPS 20A end).
4. Power: Ensure both GPS 20A and receiving device share common ground.

Tip: Use twisted pair for data wires to reduce electromagnetic interference.

Configuration & Output

GPS 20A outputs standard NMEA 0183 sentences automatically when powered and tracking satellites.

1. Default output: GGA, GLL, GSA, GSV, RMC, VTG, ZDA sentences transmitted once per second.
2. No user configuration: Unit operates with factory settings; baud rate fixed at 4800.
3. Data verification: Use NMEA monitor software or compatible device to verify data stream.
4. Sentence selection: Some devices allow filtering of specific NMEA sentences; consult your device manual.

WARNING! Do not attempt to reconfigure baud rate or output format. Unit is factory preset for standard NMEA 0183 operation.

NMEA 0183 Data

Primary sentences output by GPS 20A:

Sentence	Description	Key Data
GGA	Global Positioning System Fix Data	Time, position, fix type, satellites used, HDOP, altitude, geoid separation
GLL	Geographic Position - Latitude/Longitude	Latitude, longitude, UTC time, status
GSA	GNSS DOP and Active Satellites	Mode, satellites used, PDOP, HDOP, VDOP
GSV	GNSS Satellites in View	Satellites in view, satellite ID, elevation, azimuth, SNR
RMC	Recommended Minimum Specific GNSS Data	Time, date, position, speed, course, magnetic variation
VTG	Course Over Ground and Ground Speed	True course, magnetic course, ground speed
ZDA	Time & Date	UTC time, day, month, year, local zone

Care & Maintenance

Periodically inspect unit and connections for damage or corrosion.

1. Cleaning: Use mild soap and water on exterior. Rinse with fresh water after saltwater exposure.
2. Cable inspection: Check for cuts, abrasions, or pinched cables. Ensure connectors are clean and dry.
3. Mounting check: Verify mounting hardware remains secure, especially in high-vibration environments.
4. Connection check: Ensure all electrical connections remain tight and corrosion-free.

CAUTION! Do not use high-pressure spray near connectors. Do not disassemble unit; no user-serviceable parts inside.

Regulatory Information

FCC Compliance: This device complies with Part 15 of the FCC Rules. Operation is subject to the condition that this device does not cause harmful interference. CE Compliance: Meets applicable EU directives. Contains FCC ID: IPH-00209. For detailed regulatory information, visit www.garmin.com/compliance. Copyright © Garmin Ltd. or its subsidiaries. Garmin and the Garmin logo are trademarks of Garmin Ltd. or its subsidiaries, registered in the USA and other countries. For support, visit support.garmin.com or contact your local Garmin dealer.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No power (LED off)	Power connection issue	Check voltage at red/black wires (6-40 VDC). Verify polarity. Check fuses.
LED solid red (no fix)	Poor satellite visibility	Ensure clear view of sky. Move away from obstructions. Allow more time for acquisition.
LED flashing green	Acquiring satellites	Normal during startup. Wait up to several minutes for solid green.
No data output	Wiring or device issue	Verify NMEA connections (blue/brown wires). Check device NMEA input settings. Test with known-working device.
Inaccurate position	Multipath interference	Move away from large reflective surfaces. Ensure antenna has clear sky view.
Intermittent operation	Loose connection	Check all connections for tightness. Inspect cable for damage.

Factory Reset: Disconnect power for 10 minutes to clear almanac (forces cold start).

Service: Unit contains no user-serviceable parts. Contact Garmin Product Support or authorized dealer for service.