>>585090>I find the GPS fix to take long, but I'm the only oneLike 2-3 minutes long, or like 15 minutes long?
GPS needs 3 pieces of data to figure out where it is.
1, "Almanac". This is the rough satellite constellation. The entire package is split into little chunks that go with each GPS packet. A single satellite has to be in range of the receiver for ~12.5 minutes before the receiver has the entire almanac data package.
2. Ephemeris data - Information on the orbit of the satellite itself. If you're cold-starting the receiver, it'll have ephemeris long before it has almanac.
3. Time. Each satellite carries a Cs-atom standard "atomic clock"... that time is transmitted with each packet, so that's pretty quick.
Once the GPS knows the date/time, where all the satellites are, and the orbits of each satellite, it can locate a ray from (0, 0).... center of the planet. This is your lat/long.
Combine that with the datum (NAD83 or WGS84 are the common ones), that lat/long relates to a point on a map.
If the receiver takes 15-ish minutes to boot, it's losing that almanac/ephemeris and doing a cold-start every time. There's a small coin-cell or lithium backup battery in the receiver to hold that memory info. If that battery fails, the constant cold-boots are a symptom of that.
A "Warm start" is where the receiver's moved far enough or the ephemeris data has expired... almanac data's still valid, so once it locks in date/time and calculates a rough position from a couple satellites, it can reorient itself with the almanac data and figure out what other satellites to track. This can take a minute or two, depending on how far off position/time are.
"Hot-start" is a simple time-sync and go... almanac/ephermis data are valid in the unit.
That brown disc standing off the board is the coin cell battery in my ancient GPS. Added the shield under the antenna/RF circuit to block out some engine noise that made the receiver go crazy.
