Battery saving mode GPS 60

[sigwx]

Hi I am a recent convert to GPS for finding my way around the great outdoors.

I have been reading many of the posts and educating myself on the pros and cons of GPS use. It is a lot more complex than I expected.

One question I would appreciate advice on regards the degraded accuracy of units when operating in battery saver mode. Is this a real phenomenon or merely a perception of some users?

 

Thanks for any help.

 

Sigwx Scotland

[+fratermus]

One question I would appreciate advice on regards the degraded accuracy of units when operating in battery saver mode. Is this a real phenomenon or merely a perception of some users?

 

My unscientific perception is that it makes a big difference when working with small distances (geocaching) or when moving quickly toward autorouted turns (ie driving).

 

I wish there was a mode where it would go normal within 1/10 of a mile from a navigation endpoint (geocache/waypoint) or 5/10ths mile from a turn, then flip back to powersaver afterwards.

[+LetterDude]

On my 60CSx accuracy seems to average around 10 feet in regular mode and 20-40 feet on battery-saver mode. YMMV.

 

Craig

[+CheshireFrog]

On my 60CSx accuracy seems to average around 10 feet in regular mode and 20-40 feet on battery-saver mode. YMMV.

 

That's because battery saver mode turns off WAAS.

[+fratermus]

On my 60CSx accuracy seems to average around 10 feet in regular mode and 20-40 feet on battery-saver mode. YMMV.

 

That's because battery saver mode turns off WAAS.

 

If that is the the causal relationship, then the poster should see the same accuracy readings with battery-saver on, and with batter saver off with WAAS off. (we both assume here that he is talking about the accuracy data provided by the GPSr, and not his perception of GPS accuracy).

 

FWIW, I don't turn WAAS on ever and still have a perception that the GPSr is less useful for geocaching and tight autorouting when BS is on.

[sigwx]

Thanks for the feedback - appreciate it.

WAAS isn't available over here so that is not an issue - I will try a few experiments and see what results I get. I don't really understand why battery saver mode affects the accuracy but it seems from what some of you are saying that it does.

Thanks again.

[Frabble]

Battery Saver mode involves turning the GPS receiver off. From what I could see with my 76CSx, after a short period of satellite lock and the unit stationary, the receiver is turned off and only briefly turned on every 2 seconds.

Since the current draw with the receiver on is about 2-3 times that of when it is off, I imagine the battery running time you get could be greatly extended.

 

What it takes to go back on all the time I don't know - I couldn't easily move with the measuring kit attached, but I guess any uniform motion will let the unit predict where it will be for position and get immediate satellite lock when the receiver is turned on each time.

 

But, updates every 2 instead of 1 seconds will affect the accuracy accordingly.

Edited May 4, 2007 by Frabble

[+dumketu]

On my 60CSx accuracy seems to average around 10 feet in regular mode and 20-40 feet on battery-saver mode. YMMV.

 

That's because battery saver mode turns off WAAS.

 

Yes it does, but WAAS makes no difference to the accuracy of my 60CSx. I wonder if the battery saver mode turns off the receiver for brief periods (1s or less) whereas the regular mode leaves the receiver on all the time?

[+fratermus]

What it takes to go back on all the time I don't know - I couldn't easily move with the measuring kit attached, but I guess any uniform motion will let the unit predict where it will be for position and get immediate satellite lock when the receiver is turned on each time.

 

I think that lack of uniform/predictable motion is what makes geocaching with Battery Saver on a suboptimal experience. When I'm wandering around in circles the GPSr can't predict where I ought to be the next time the receiver cranks up.

[+apersson850]

In normal mode, the GPS receiver circuit feeds the navigator with new position data every second. In battery saver mode, it still does that, but interpolate three out of four (or so, it varies a bit) positions, thus actually running the receiver only a quarter of the time.

 

As you have already figured out, this is not too important when you are moving at a fairly consistent speed and direction, but if you are moving erratically, there will be errors in between readings. On the other hand, moving like that is likely to reduce the effect of battery saver mode, as the receiver software will have to let the hardware run a bit more, to make sure where you have strolled away.

 

Crucial Egnos/WAAS data is transmitted every second, which explains why it's incompatible with battery saver mode.

The EPE (Estimated Position Error) is some fancy math done by the GPS unit. Nothing prevents them to be more pessimistic in battery saver mode, even if the actual satellite signals are just as good. This then to give the (often correct) impression that the result is a bit inferior in battery saver mode.

[sigwx]

Thanks - it seems that using battery saver is fine, for wandering the hills on the move, but when it gets tricky then switch back to normal operation.

 

Thanks everyone

 

sigwx

[Hertzog]

Thanks for the feedback - appreciate it.

WAAS isn't available over here so that is not an issue - I will try a few experiments and see what results I get. I don't really understand why battery saver mode affects the accuracy but it seems from what some of you are saying that it does.

Thanks again.

It's not so much a matter of turning off WAAS; this has a relatively minor effect. The main effect of the power save mode is to reduce the update rate from 1 second to 5 seconds. This has a major effect on the accuracy. LetterDude indicated he sees a 2 to 4 factor increase in error; my experience (the few times I've checked it) is on the high end of this - a factor of 4 or 5. You can see it in the "Accuracy" calculation of the GPSr, and in addition you can see it in the increased scatter that you get just leaving the unit stationary for a while (even when moving the increased scatter about your path is obvious, but harder to quantify).

 

Sorry for the redundancy. I didn't see aperrson850's post before posting this; looks like he said it better.

Edited May 6, 2007 by Hertzog

[+hogrod]

Thanks - it seems that using battery saver is fine, for wandering the hills on the move, but when it gets tricky then switch back to normal operation.

 

Thanks everyone

 

sigwx

 

my legendC never had any issues with loosing lock when held properly, unitl one day I accidentally used battery saver mode.

On my 60cx I decided to check position errors when using battery saver, the claimed accuracy in my house went from 20ft to 75ft in a matter of a minute. even worse the 60cx claimed accuracy was correct at 75ft, the numbers the unit were giving were way off from reality.

I would only use battery saver mode i I was lost in the woods and really needed to conserve power, otherwise it causes to many issues.

[sigwx]

Yep it makes a difference - I had my first geocache trip yesterday and there was a definite improvement in the accuracy of the unit especially during that crucial last few yards.

Hey geocaching is more fun than I thought it would be. Didn't get the gps for that but I could get hooked if I am not careful.

 

Sigwx

[+apersson850]

It's also during the last few meters to the cache that you are most likely to move erratically back and forth, a situation battery saver mode has less capability to handle.