โAug-09-2013 04:21 PM
โAug-11-2013 08:51 AM
โAug-11-2013 08:35 AM
โAug-10-2013 05:50 AM
โAug-09-2013 09:41 PM
โAug-09-2013 08:40 PM
โAug-09-2013 06:34 PM
bob_nestor wrote:
Actually the ephemeris data does tell the GPS unit where the satellites are in the sky and that speeds the processing done to correctly locate your ground position. The ephemeris data "ages" due the the satellites not being in an absolute geosynchronous orbit. It is good for about two weeks. The updated data can be downloaded to the ground unit from the satellites or preloaded. Usually on an initial setup of a GPS unit that doesn't have current data it will take longer to acquire the satellites and compute your ground position. GPS units that have been more recently used will tend to acquire quicker because they have more up to date information. That's why on some units (like military GPS) they pre-load the units before going on a mission. They're loading current ephemeris data and may also load the decode keys to access the higher precision signals not available to non-military users. But you are correct in how the GPS uses time and signal phase differences to compute ground position.
โAug-09-2013 06:29 PM
n7bsn wrote:WoodGlue wrote:
Sorry about the mess with the text not wrapping. I wrote this offline and I'm not about to write it out again!
...
๐ GPX "Quick Fix" This is done via your computer and the almost daily updates from TomTom. It tells the unit where in the sky to look for the satellites. This feature is updated every few days, at lest it is the case for my XL 335 M - It's very nice that the TomTom will know the general area where to search - It speeds any kind of delay....
WoodGlue
I'm sorry you have bit into this complete bit of marketing. That's all it is. Period.
No GPS on the market (and I've used consumer, military, commercial navigation, etc) can "know" where to look in the sky for the GPS satellites, nor would you want them to.
Every GPS has an omnidirectional antenna, meaning the antenna "listens" in all directions, equally.
Since the GPS is listening to multiple satellites at a time, with a non-directional antenna the idea that the GPS is "looking" for a special area of the sky is complete BS.
How your GPS works is it each Satellite sends out time mark signals, the GPS measures the difference in arrival time for the time signals. and computes your location based on these signal.
โAug-09-2013 05:53 PM
n7bsn wrote:
I'm sorry you have bit into this complete bit of marketing. That's all it is. Period.
No GPS on the market (and I've used consumer, military, commercial navigation, etc) can "know" where to look in the sky for the GPS satellites, nor would you want them to.
Every GPS has an omnidirectional antenna, meaning the antenna "listens" in all directions, equally.
Since the GPS is listening to multiple satellites at a time, with a non-directional antenna the idea that the GPS is "looking" for a special area of the sky is complete BS.
How your GPS works is it each Satellite sends out time mark signals, the GPS measures the difference in arrival time for the time signals. and computes your location based on these signal.
โAug-09-2013 05:46 PM
WoodGlue wrote:
Sorry about the mess with the text not wrapping. I wrote this offline and I'm not about to write it out again!
...
๐ GPX "Quick Fix" This is done via your computer and the almost daily updates from TomTom. It tells the unit where in the sky to look for the satellites. This feature is updated every few days, at lest it is the case for my XL 335 M - It's very nice that the TomTom will know the general area where to search - It speeds any kind of delay....
WoodGlue
โAug-09-2013 05:24 PM
โAug-09-2013 04:44 PM
fj12ryder wrote:
Now that's a fair comparison. LOL Just a little biased towards the Tom-Tom? ๐
โAug-09-2013 04:38 PM