I'm just looking at the number of satellites my 1490T is using (11) and on the graph it appears that it has the potential to receive and use one more.
I'm just wondering what is the maximum number of satellites in the constellation that could be above the horizon at one time for any given place?
"The satellite orbits are distributed so that at least 4 satellites are always visible from any point on the Earth at any given instant (with up to 12 visible at one time)."
According to this reference, 12.
While it has been pretty uncommon, I have seen a single receiver show 12 currently active satellites at a time more than once here in Albuquerque. And in one memorable instance I had two different receivers showing 12 each, and they weren't the same 12.
One issue is that the constellation currently has more satellites active than the 24 the original system plan contemplated. I think there is probably a hard limit of no more than 32 active satellites, as I think there is a five bit satellite number for that purpose.
See this reference for the situation in November, 2009, when of 35 birds in orbit, 30 were set healthy to users and thus could show up on your screen.
My Garmin handheld supports WAAS, and thus has one or two birds to choose from.
Great question. Does anyone know the MINIMUM number of statelites to get the GPS going?
I had thought 4 but according to http://wiki.answers.com/Q/How_many_minimum_satellites_are_re... . 3 will do it.
This article also states 3 http://www.rmsizzling.com/tag/gps-satellites
At least 3 is needed to triangulate your position. I didn't read those articles.
Just for the heck of it I grabbed my Nuvi 1300 WT and stepped out into my driveway. Turned it on and within less than 2 minutes I had 11 satellites locked on with all 11 columns being shown fully blued in with 100% power.
The satellites were #'s 3, 6, 7, 8, 11, 13, 17, 19, 23, 24 & 28. My screen also showed I had 7 foot accuracy.
As far as I'm concerned that's good enough for me. Are my results considered normal as to total locked on satellites and accuracy.. or should I be looking for results that are better or worse than that?
The earth's surface counts as the 4th sphere in triangulating a location in 3D space, so only three GPS sats are needed even though in geometry, four spheres are needed for 3D triangulation:
.. Are my results considered normal as to total locked on satellites and accuracy.. or should I be looking for results that are better or worse than that?..
I'd say it's pretty good. I think it depends mainly on your unit, your immediate surroundings, and somewhat on your lat/lon, but I'm no expert.
Just so we can compare, my driveway/house is in a little bit of a ravine with a lot of trees all dirs, my unit just used was a 200W, and my coords are 39.03/76.59 (MD) and I got 7 sats locked, 3 more off & on, 22 ft accuracy.
3 (satellites) measurements are required to "triangulate" a position. However, GPS needs a 4th satellite to provide a 3D position. Why??
Three measurements can be used to locate a point, assuming the GPS receiver and satellite clocks are precisely and continually synchronized, thereby allowing the distance calculations to be accurately determined. Unfortunately, it is impossible to synchronize these two clocks, since the clocks in GPS receivers are not as accurate as the very precise and expensive atomic clocks in the satellites. The GPS signals travel from the satellite to the receiver very fast, so if the two clocks are off by only a small fraction, the determined position data may be considerably distorted.
The atomic clocks aboard the satellites maintain their time to a very high degree of accuracy. However, there will always be a slight variation in clock rates from satellite to satellite. Close monitoring of the clock of each satellite from the ground permits the control station to insert a message in the signal of each satellite which precisely describes the drift rate of that satellite's clock. The insertion of the drift rate effectively synchronizes all of the GPS satellite clocks.
The same procedure cannot be applied to the clock in a GPS receiver. Therefore, a fourth variable (in addition to x, y and z), time, must be determined in order to calculate a precise location. Mathematically, to solve for four unknowns (x,y,z, and t), there must be four equations. In determining GPS positions, the four equations are represented by signals from four different satellites.
Source for above statement: http://www.cmtinc.com/gpsbook/
GPS Operational Satellites in your sky right now:
(Click on the satellite name and track it.)
The minimum number of satellites for a receiver operating in timing mode with a fixed, known location is: 1.
These are the GPS receivers used in cell towers to provide accurate time and frequency references, and in many industrial locations, also for providing time and frequency references.
For around $100 and an outdoor GPS antenna, you can have time and frequency references with the same accuracy as the clocks on the GPS birds -- go to eBay and look for "Thunderbolt GPS."
I have been using n2yo for quite a while now and there is an unbelievable amount of information there. All kinds of really interesting stuff.
i average round 8
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