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Satellite Constellations
Your Global Positioning System receiver (GPSr) must utilize information transmitted from one or more of the following GPS satellite constellations to accurately and precisely calculate your current position. Which systems are used and the number of satellite signals available will impact performance.
GPS
The Global Positioning System is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The original concept for a Defense Navigation Satellite System (DNSS) in September 1973 was later named Navstar (NAVigation System using Timing And Ranging), then Navstar-GPS to identify the constellation of Navstar satellites, and eventually shortened simply to GPS. Achieving initial operational capability (IOC) in December 1993, Full Operational Capability (FOC) was declared by Air Force Space Command (AFSPC) in April 1995. The highest quality signals were reserved for military use, and the signal available for civilian use was intentionally degraded. Selective Availability was discontinued on May 2, 2000, allowing users to receive a non-degraded signal globally. GPS is maintained by the United States government and is freely accessible to anyone with a GPS receiver.GLONASS
The GLObal NAvigation Satellite System is a space-based satellite navigation system operated by the Russian Aerospace Defence Forces. It both complements and provides an alternative to the United States' Global Positioning System (GPS) and is the only alternative navigational system in operation with global coverage and comparable precision. GLONASS initially achieved Full Operational Capability (FOC) in December, 1995. Financial difficulties crippled the Russian space program, leaving them with only 6 operational satellites by 2001. In 2010, GLONASS had achieved 100% coverage of Russia's territory, and by October 2011, the full orbital constellation of 24 satellites was restored, enabling full global coverage.GBAS
The Ground Based Augmentation System (also referred to as Local Area Augmentation System in U.S.) is intended primarily to support precision aviation approach operations. GBAS information is transmitted using VHF signals the Montana is not equipped to receive.SBAS
A Satellite Based Augmentation System supports wide-area or regional augmentation through the use of additional satellite-broadcast messages.WAAS
The Wide Area Augmentation System is a satellite based augmentation system (SBAS) jointly developed by the United States Department of Transportation (DOT) and the Federal Aviation Administration (FAA). WAAS was commissioned for use on July 10, 2003.EGNOS
The European Geostationary Navigation Overlay Service is a satellite based augmentation system (SBAS) developed by the European Space Agency, the European Commission, and EUROCONTROL. EGNOS operations were initiated in July 2005. An EGNOS Data Access Service was made available in July 2012.MSAS
The Multi-functional Satellite Augmentation System is a Japanese satellite based augmentation system (SBAS) commissioned on September 27, 2007.GAGAN
The GPS Aided Geo Augmented Navigation is a regional satellite based augmentation system (SBAS) implemented by the government of India. GAGAN is scheduled to be fully operational in early 2014.Satellite Identification
Have you ever considered what the numbers assigned to each GPS satellite on your Garmin GPSr represent, or how they are determined?PRN
Global positioning systems use a form of spread-spectrum or code-division multiple access (CDMA) communications where each signal source is modulated by a PRN (pseudo-random noise) code. The PRN code (along with other encoded sub codes) dithers the L1 carrier (or the coarse-acquisition carrier) of the signal. All receivers listen on the same L1 frequency, but they sort out the satellite signals by demodulating them according to their PRN encoding.NMEA
Garmin GPS receivers employing the NMEA 0183 specification assign each GPS satellite signal a unique NMEA identification number based on the satellite PRN number (GPS) or slot number (GLONASS):| PRN |
Standard Assignment |
NMEA |
Garmin Assignment |
Garmin NMEA Conversion |
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| 01-32 |
GPS |
01-32 |
GPS |
NMEA = PRN |
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| 33-63 |
GPS |
33-63 |
SBAS |
NMEA = SBAS PRN - 87 |
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| 64-96 |
GBAS |
65-88 |
GLONASS |
NMEA = GLONASS Slot Number + 64 |
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| 97-119 |
GBAS |
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| 120-158 |
SBAS |
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| 159-210 |
Future GNSS |
Satellite Tracking
- Select individual satellites from the list below to view current status, location and detailed information.
- Compare current satellite locations against the Satellite application display on your GPSr.
What's Up?
- Have you ever wondered what satellites and other low orbit objects are flying over you right now?
- View all available GPS satellites positioned at minimum 20° above the horizon for your current location.
- View all available SBAS satellites positioned at minimum 20° above the horizon for your current location.
- View all available GLONASS satellites poitioned at minimum 20° above the horizon for your current location.
- View all satellites positioned at minimum 60° above the horizon (directly overhead) for your current location.
- View current GPS constellation status reports.
- View current GLONASS constellation status reports.
