Have you ever wondered how your sat nav receiver uses satellite signals to calculate your exact location on the Earth's surface? Here's a non-technical explanation to satisfy your curiosity. The first factor you need to know is that your receiver has to get a signal from at the very least four satellites in order to calculate your location. You'll find currently about 30 GPS satellites orbiting the Earth, and at least 8 are in a direct line of sight with a given point on the Earth's surface at all times. So so long as you are not deep underground, satellite reception is rarely a problem for receivers.
The only factor your sat nav receiver knows about a single GPS satellite is its distance from you. It determines this by sending a signal to the satellite and receiving a response. Due to the fact radio signals often travel at the speed of light, the delay in response permits the receiver to calculate how far away the satellite is. But with only a single satellite, your receiver has no way of determining what direction the signal is coming from. Should you picture a sphere centred on the GPS satellite, along with the radius of the sphere is the distance between it and your receiver, your location might be anywhere on the surface of the sphere.
This is why multiple satellites are needed. Say your GPS receiver repeats this method having a second satellite. You now have two spheres, but because your location is on the surface of both spheres, you can now narrow it down to somewhere along the intersection of these two spheres. The intersection of two spheres is a circle. But you could still be located anywhere around the circle. So add a third satellite as well as a third sphere. A circle intersects a sphere at only two points, so you now know that your location is one of those two points. At this point, your sat nav device could basically assume that you are at the point that is in fact on the Earth's surface and be performed.
The problem with using only 3 satellites is that the clock in your sat nav receiver is not 1 hundred percent accurate. Being off by even a tiny fraction of a second can throw off the calculations, given that such big numbers are involved. This is why the signal from a fourth GPS satellite is necessary.
If your receiver's clock had been perfect, the fourth satellite's calculated sphere would intersect one of the two points mentioned above. But considering that your clock isn't excellent, it will be off slightly. In this case, all your receiver has to do is measure the distance between this point along with the surface of the fourth sphere. It then uses this distance to right for any clock inaccuracies. And that is how the Global Positioning Program locates you.
The only factor your sat nav receiver knows about a single GPS satellite is its distance from you. It determines this by sending a signal to the satellite and receiving a response. Due to the fact radio signals often travel at the speed of light, the delay in response permits the receiver to calculate how far away the satellite is. But with only a single satellite, your receiver has no way of determining what direction the signal is coming from. Should you picture a sphere centred on the GPS satellite, along with the radius of the sphere is the distance between it and your receiver, your location might be anywhere on the surface of the sphere.
This is why multiple satellites are needed. Say your GPS receiver repeats this method having a second satellite. You now have two spheres, but because your location is on the surface of both spheres, you can now narrow it down to somewhere along the intersection of these two spheres. The intersection of two spheres is a circle. But you could still be located anywhere around the circle. So add a third satellite as well as a third sphere. A circle intersects a sphere at only two points, so you now know that your location is one of those two points. At this point, your sat nav device could basically assume that you are at the point that is in fact on the Earth's surface and be performed.
The problem with using only 3 satellites is that the clock in your sat nav receiver is not 1 hundred percent accurate. Being off by even a tiny fraction of a second can throw off the calculations, given that such big numbers are involved. This is why the signal from a fourth GPS satellite is necessary.
If your receiver's clock had been perfect, the fourth satellite's calculated sphere would intersect one of the two points mentioned above. But considering that your clock isn't excellent, it will be off slightly. In this case, all your receiver has to do is measure the distance between this point along with the surface of the fourth sphere. It then uses this distance to right for any clock inaccuracies. And that is how the Global Positioning Program locates you.
About the Author:
Abe Ford is an expert in Quality Sat Nav Voice and related topics. To learn more, visit http://www.satvoices.com today!
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