GPS Map60CSX question

[DougPaul]

don't I know it I have a lowrance ifinder and the thing seems to have "lost confidence" in the last few months (used to acquire lock quickly), it gets GPS lock but then won't get an EPE smaller than 100m, it takes it about 15-20 minutes with good reception (no/few trees) to finally get its act together. and my battery door broke after < 18months of use, and I never hear back from the customer service people. I may be looking at Garmins next spring.

It is acting as if it is doing a cold start. If you haven't used it in quite a while, this is to be expected.

What happens if you obtain a lock and then power-cycle the GPS. How long does it take to reacquire a lock?

Some GPSes have a backup battery to power a clock and some memory so that the GPS can remember the time, almanac, ephemeris, and last location. If this battery is dead, then you are always doing a cold start even if you only power cycle the GPS. In some GPSes, this battery is rechargable. Try leaving fresh batteries in the GPS for a day or so to see if it charges the backup battery.

Garmin seems to be running away with the consumer GPS market...

Doug

 

[Paradox]

Garmin seems to be running away with the consumer GPS market...

I think I heard an ad for Garmin on one of the NFL playoff games last season! Their units are just so much "slicker" and just plain usable than my Magellin Platinum. Magellin is probably in second place. IMHO Garmin is going for the brass ring and has the product to do it with.

Lets do it! Sounds like fun.

I'm alway serious about fun! Let's do some sort of field test! You design the study, I'll play grad student.

 

[arghman]

Some GPSes have a backup battery to power a clock and some memory so that the GPS can remember the time, almanac, ephemeris, and last location. If this battery is dead, then you are always doing a cold start even if you only power cycle the GPS. In some GPSes, this battery is rechargable. Try leaving fresh batteries in the GPS for a day or so to see if it charges the backup battery.

Interesting. Probably not in the case of the Lowrance iFinder, but I will ask. There does not appear to be an RTC; every time I turn it on, it says 7pm. (vs. my Garmin which does have an RTC) The clock on the iFinder doesn't adjust until it acquires lock (which is insane, it should be able to get a time signal from just 1 GPS, right?) However, if I acquire lock, turn it off, then on again, it almost re-acquires lock quickly, which tells me that it's remembering something...

 

[DougPaul]

Interesting. Probably not in the case of the Lowrance iFinder, but I will ask. There does not appear to be an RTC; every time I turn it on, it says 7pm. (vs. my Garmin which does have an RTC) The clock on the iFinder doesn't adjust until it acquires lock (which is insane, it should be able to get a time signal from just 1 GPS, right?) However, if I acquire lock, turn it off, then on again, it almost re-acquires lock quickly, which tells me that it's remembering something...

The clock display is certainly suspicious. Or perhaps the GPS knows the proper time, but doesn't bother to display it until it gets a fix.

A GPS can get the approximate time (to within a few hundred msec) from the first satellite because the maximum time-of-flight of the signal is a few hundred msec (1 msec = 1/1000 second). This is good enough to significantly reduce the acquisition time. (The internal clocks can easily drift more than this in a few days.) Once a 4 (or more) satellite fix is obtained, the GPS knows the time to within a few nsec (billionths of a sec). The front-panel display is generally accurate to a second or so. (There are GPS-based time references with outputs accurate to less than a usec (micro-second, millionth of a sec).

It is possible that the backup battery is mostly dead--it can hold a charge for a short time. Others have had problems with backup batteries. You may be able to find additional info by searching sci.geo.satellite-nav http://groups.google.com/group/sci.geo.satellite-nav?lnk=gschg&hl=en or http://gpsinformation.net.

Doug

 

[DougPaul]

I'm alway serious about fun! Let's do some sort of field test! You design the study, I'll play grad student.

I suppose we could play investigator.

But first a bit of research:
(Primarily by going to http://groups.google.com/group/sci.geo.satellite-nav?lnk=lr&hl=en and searching and checking my bookmarks, etc).

Note: there have been several outstanding problems with the 60CSx/76CSx (identical except for the case):
1.) Does not reacquire lock after exiting tunnels. Fixed.
2.) Difficulty acquiring WAAS satellites. Fixed, I think.
3.) Shuts down with new lithium batteries. Not fixed (presumably a hardware problem.)
4.) Slow to acquire satellites if you are moving. Not fixed--looks inherent.
5.) Excessive tracklog consumption. Status?

Some interesting notes found during the research:
* the 60CSx doesn't use an almanac because it can search so quickly. An ephemeris is good for up to 4 hrs, so the restart time within 4 hrs is much faster than over 4 hrs. (There is one report of longer than 15 min when walking, but a very quick fix after stopping.) (Dale DePriest http://users.cwnet.com/dalede/ )
* The standard Garmin chipset does not show satellites with S/N ratio
below 30 and will often track at that same level while the SiRF chipset
will report satellites below the level that it can actually track them.
In addition the SiRF III can actually track satellites with a S/N ratio
below 20. (Dale DePriest)


I found a nice comparison between the 60CS and 60CSx:
http://patrick-roeder.de/reviews/garmin_gpsmap_60CSx.htm
It suggests the 60CSx is more accurate than the 60CS in degraded conditions. Lots of other good stuff--worth reading.

I recall someone in the UK doing a study of accuracy while hiking. I recall thinking that it was well done, but couldn't find it. I probably have it bookmarked somewhere.

Assorted other tests:
http://www.gpsmap.net/WaldoTestIntroduction.html

Doug