GPS Sync Tip

[kmorgan]

I have seen several threads over the years regarding GPS units and how long they take to sync up with satellites when first turned on.

Generally the threads concern a sudden increase in how long syncing up takes. I have never had a problem with my Garmin GPS 60CS until last weekend at Peekamoose trailhead. My unit just took forever to lock onto the satellites!

I did figure out what was causing the problem. You see, I use my GPS every weekend so I always have batteries in the unit. Last week I needed a AA battery for a small clock, so since the batteries in my GPS were only about 8 hours old I took them out and used one for the clock. I intended to use fresh batteries on the weekend so no big deal.

I didn't replace the GPS batteries until Saturday, so 4 days had lapsed and when the GPS tried to find the satellites it was looking for the wrong ones in the wrong place. As far as the unit was concerned I had traveled thousands of miles plus the clock didn't match up. Even when I placed the location for search right at the trail head it wouldn't lock up. I finally put it in auto locate mode and it synced up nicely after a few minutes.

So if you use your unit a lot always keep fresh batteries in it so the clock and calendar are up to date.

Kevin

 

[DougPaul]

What you experienced was a "cold" start.

There are 3 kinds of start for most GPSes:
* A hot start (current almanac and ephermeris, known starting location (eg turn the GPS off then back on within a few minutes without moving)) can give you a fix in 15 or so seconds.
* A warm start (current almanac, known starting position (eg turn GPS off, wait a few hours, and turn it back on without moving it any significant distance) ~45 sec.
* A cold start (the GPS has been turned off for days, no almanac, or unknown location): ~3 min.

(All of the above times assume a good skyview and assume that WAAS is turned off--WAAS can take a lot longer to get going.)

Some of the more recent high sensitivity GPSes appear not to use the almanac so they only have hot and cold starts, but for other reasons tend to start faster than the above times. (The 60Cx and 60CSx have cold start times ~45sec.)

defs:
* almanac=coarse orbital info, used for acquiring sats, broadcast by all sats
* ephemeris=accurate orbital info, used for navigation, broadcast by each sat for itself only

Doug

 

[sardog1]

A powercord adapter that plugs into your vehicle's twelve volt system goes a long way to solving this issue. Plug in the GPS receiver when you roll down the driveway at home. Switch to battery power at the trailhead. Might save you the embarrassment of delaying your trail companions (or the law enforcement officer that's going to accompany you on the search . . . )

 

[Paradox]

Another nice tip I believe I picked up from DougPaul was keeping the unit stationary. Starting up the trail or otherwise moving the unit around will increase the time for satellite link up considerably.

 

[Papa Bear]

Another nice tip I believe I picked up from DougPaul was keeping the unit stationary. Starting up the trail or otherwise moving the unit around will increase the time for satellite link up considerably.

I usually stick it in the open on the hood of the car while we get our packs, water, boots etc. ready.

One problem: I was with Oncoman last year and we parked my car as a spot and got our stuff together and then piled into his car to get to the start. Guess what?, after about 2 slow miles on a logging road, I realized it was back on my car's hood!! Oncoman was nice enough to turn a round so I could get it. Lost about 20 minutes!

BUT it was really synched!

 

[Neil]

Here's one for DP. On several occasions while driving to the TH I have turned the gps on in the car and have locked onto 4 or 5 satellites in less than a minute. Then I turned it off. Once underway on the hike I turned it on again only to have it take at least 15 minutes to lock. The distance between the two locks was less than 30 miles. Prior to the first lock I last used it 150 miles away.

(I think we should start a new VFTT sub-forum entitled, "Dear Doug")

 

[DougPaul]

Here's one for DP. On several occasions while driving to the TH I have turned the gps on in the car and have locked onto 4 or 5 satellites in less than a minute. Then I turned it off. Once underway on the hike I turned it on again only to have it take at least 15 minutes to lock. The distance between the two locks was less than 30 miles. Prior to the first lock I last used it 150 miles away.

Which GPS and what was the skyview like?

I've lost an established lock while walking with a GPS under tree cover. A worse situation than you describe above. (All you have to do is start your hike under appropriate tree cover to explain your situation.) Presumeably less of a problem with the new high sensitivity GPS chipsets.

(I think we should start a new VFTT sub-forum entitled, "Dear Doug")

I think I should start charging for GPS advice... I'd make a mint!

Doug

 

[Neil]

Which GPS and what was the skyview like?

RINO 130, moderate and dry deciduous canopy. Several pauses under canopy open 360 degrees down to 45 degrees from horizon.

I think I should start charging for GPS advice... I'd make a mint!

Doug

Dear Doug, I think my gps is out to kill me, it all started when... Can I lobotomize it?

 

[Paradox]

"Dear Doug")

I hardwired my GPS into my car. My intention is to get a little extra snooze time on the way to the trailhead. Can you check my schematics for me, and get back to me before the weekend? Thanks a million!

 

[DougPaul]

Dear Doug, I think my gps is out to kill me, it all started when... Can I lobotomize it?

Sure you can. But don't ask me why it stops telling you where you are...

Doug

 

[DougPaul]

I hardwired my GPS into my car. My intention is to get a little extra snooze time on the way to the trailhead. Can you check my schematics for me, and get back to me before the weekend? Thanks a million!

I've "forgotten" how to read schematics, but I do remember how to use hammers and wire clippers...

Doug