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 very first factor you should know is that your receiver has to get a signal from a minimum of four satellites so that you can calculate your location. You will find currently about 30 GPS satellites orbiting the Earth, and at the very least 8 are in a direct line of sight having a given point on the Earth's surface at all times. So as long as you're not deep underground, satellite reception is rarely a issue for receivers.
The only thing 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 constantly travel at the speed of light, the delay in response makes it possible for 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. In the event you imagine a sphere centred on the GPS satellite, along with the radius of the sphere will be the distance between it and your receiver, your location could possibly 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 since your location is on the surface of both spheres, you are able to now narrow it down to somewhere along the intersection of these two spheres. The intersection of two spheres can be a circle. But you could still be situated 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're at the point that is really on the Earth's surface and be completed.
The problem with making use of only 3 satellites is that the clock within 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, since such big numbers are involved. This is why the signal from a fourth GPS satellite is required.
If your receiver's clock were best, the fourth satellite's calculated sphere would intersect one of the two points mentioned above. But since your clock isn't ideal, 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 correct for any clock inaccuracies. And that is how the Global Positioning Program locates you.
The only thing 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 constantly travel at the speed of light, the delay in response makes it possible for 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. In the event you imagine a sphere centred on the GPS satellite, along with the radius of the sphere will be the distance between it and your receiver, your location could possibly 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 since your location is on the surface of both spheres, you are able to now narrow it down to somewhere along the intersection of these two spheres. The intersection of two spheres can be a circle. But you could still be situated 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're at the point that is really on the Earth's surface and be completed.
The problem with making use of only 3 satellites is that the clock within 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, since such big numbers are involved. This is why the signal from a fourth GPS satellite is required.
If your receiver's clock were best, the fourth satellite's calculated sphere would intersect one of the two points mentioned above. But since your clock isn't ideal, 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 correct 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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