- Thu Oct 05, 2006 10:41 am
#20038
First off, it would be helpful to know what you're doing. I doubt you'd see any difference in the performance of these modules if you were sitting on the top of the tallest building in town, or out in a wide open field. Down in an "urban canyon" with cars and tall buildings all around, and you very likely would see some differences.
SiRFstar3 is called "20 channel" because it has enough CPU power to track 20 PRNs in realtime. In a way, SS3 is a fast embedded DSP running a software-gps to track the satellite, with the on-board ARM running the navigation solution and handling the I/O. I think you'd be hard-pressed to find places where you're going to get more than 11 usable satellites. There are times during the day when I can track 11 + WAAS, but there is always one down on the horizon that's pretty much useless.
When logging GPS data, make sure you are mindful your fix quality. GPGSA gives you number of satellites used to calculate your postion and your Dilution Of Precision. If your DOP numbers are high , you need to be aware that there could be some significant discrepancies between your reported position and your position on a map. For my purposes, HDOP >= 2.0 is high. That's still perfectly acceptable for driving around town, though.
Things that can affect your fix, even with the best receivers include a poor antenna (or the antenna housing), multipath error from signals reflecting off water/buildings/metal objects, atmospheric interference from moisture or charged particles, poor visible constellation geometry, and differences in the implementation of the satellite tracking and navigation solution algorithms. Higher sensitivity receivers sacrifice some accuracy and speed for the ability to lock on to a weaker (less reliable) signal.
My SS3 receivers have been quite reliable, and I should have a Lassen iQ shortly. I suspect that if you're looking for a quick fix (pardon the pun) make sure that your antenna cable is not bent or kinked, there is no dirt or oil on your antenna, and you have an unobstructed view of as much sky as possible. Even a little bit of adhesive tape on your antenna can adversely affect signal reception.
GDB has a 'break' feature; why doesn't it have 'fix' too?