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gps receiver reviewThe GPS or Global Positioning System is a global navigation system used for military and civilian applications alike.
The GPS system uses a satellite constellation of 24 satellites in intermediate circular orbits. The orbits are designed so at least four satellites are always within line of sight from almost any place on earth. The constellation also includes three spare satellites in orbit. When it was first deployed, GPS included a feature called Selective Availability (or SA) that introduced intentional errors of up to a hundred meters into the publicly available navigation signals, making it difficult to use for guiding long range missiles to precise targets. Additional accuracy was available in the signal, but in an encrypted form that was only available to the United States military, its allies and a few others, mostly government users. In 1985, ten experimental Block-I satellites were up. A complete "constellation" of 24 satellites was in orbit by January 17, 1994. GPS receivers come in a variety of consumer formats, and today can be found in cars, watches, phones boats and planes. Major manufacturers include Trimble, Garmin and Leica, low-end, hand-held consumer units are often available at less than $100 per unit. The most recent launch was in September 2005. The oldest GPS satellite still in operation was launched in February 1989. In 1998, Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety. In early years, the US military made the civilian application purposefully less powerful than it could. But since August 2000, the GPS civilian application provides the accuracy of GPS signals to within 2 meters (6 ft). Fact is, GPS accuracy can be improved further, to about 1 cm (half an inch) over short distances, using techniques such as Differential GPS (DGPS). GPS signals can also be affected by multipath reflections of the radio signals off the ground and/or surrounding structures (buildings, canyon walls, etc). For long delay multipath signals, the receiver itself can filter the signals out. A variety of receiver techniques, most notably Narrow Correlator spacing, have been developed to mitigate multipath errors. One of biggest problems for GPS accuracy is that changing atmospheric conditions change the speed of the GPS signals unpredictably as they pass through the ionosphere. The effect is minimized when the satellite is directly overhead and becomes greater toward the horizon, as the satellite signals must travel through the greater "thickness" of the ionosphere as the angle increases. Once the receiver's rough location is known, an internal mathematical model can be used to estimate and correct for the error. Atomic clocks on the GPS satellites are set to "GPS time", which is the number of seconds since 00:00:00 UTC, January 6, 1980. UTC is short for Coordinated Universal Time. Today, GPS time is 14 seconds ahead of UTC, because it does not follow leap seconds. That's why new GPS units initially show the incorrect time after achieving a GPS lock for the first time. However, this is usually corrected on the display within 15 minutes once the UTC offset message is received for the first time. During the Gulf War, the shortage of military GPS units and the wide availability of civilian ones among personnel resulted in disabling the Selective Availability. In the 1990s the FAA started pressuring the military to turn off SA permanently. This would save the FAA millions of dollars every year in maintenance of their own, less accurate, radio navigation systems. The military resisted for most of the 1990s, but SA was eventually turned off in 2000 following an announcement by then US President Bill Clinton, allowing all users to enjoy nearly the same level of access. Commercial civilian GPS receivers are purposefully less accurate than they might be. In specific, they are required to have limits on the velocities and altitudes at which they will report coordinates in order to prevent them from being used to create improvised missiles.
1. gpsinformation.net
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Sony VGPBGU1 Bluetooth GPS Receiver Reviews | 6 reviews Sony VGPBGU1 Bluetooth GPS Receiver reviews. Find Handheld GPS reviews at Buzzillions including 6 reviews of Sony VGPBGU1 Bluetooth GPS Receiver. 32. Garmin GPS 76 Handheld GPS Receiver Reviews. Buying Guides ... Epinions.com - Read product reviews on Garmin GPS 76 Handheld GPS Receiver - GPS Devices. Overall Rating: 4.5 stars from 25 consumer reviews at Epinions.com. 33. Magellan 3050T GPS receiver review - Pocket-lint Magellan 3050T GPS receiver - Can Magellan challenge TomTom and Navman with its latest creation? full review 34. GARMIN GPSmap 276C GPS Receiver/Review GARMIN GPSmap 276C GPS Receiver/Review.... garmin gpsmap 276/ garmin 276c gps/ The GARMIN GPSmap 276C GPS Receiver is right in place and that home whether its on your ... 35. Qstarz GPS travel recorder review We received a Digitrading test sample and the following review will reveal more about how the Qstarz GPS receiver worked in practice. 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