[gps-talkusers] Re: Quick Battery Discharge

Yes there is some truth to this statement Mike.

The GPS receiver keeps an internal almanac of where the satellites "should" 
be.  This almanac is updated when the GPS receiver is linked to the 
satellites.
When the unit is first turned on it starts looking where it "thinks" the 
satellites should be based on its current almanac.  If after a while it 
can't find these satellites in the positions it thinks they should be then 
it switches to a mode called Cold start where it forgets its current 
almanac and starts searching for all satellites.  This happens because as 
far as the receiver is concerned the satellites should be in a particular 
position at a particular time for this particular part of the country but 
they aren't so the receiver starts over from scratch as if you just moved 
the receiver half way around the planet, and it rebuilds it almanac of 
where the satellites are.

Cold start or cold boot as they call it can take a while to obtain a GPS 
fix 5-10 minutes if you are lucky when out in an open area and the 
satellites are in a favorable geometry.

Warm start or warm boot usually takes less than a minute when the gps 
receiver has an updated almanac of where the satellites are for the last 
lat/lon the receiver was switched off at, and you are not too far from that 
last position when you turn on your GPS receiver.

Hot start usually takes less than 20 seconds, and this occurs with some 
receivers if you just turn off your GPS receiver and turn it back on within 
30 minutes or so at the same location.

Therefore if you are inside and turn on your GPS receiver it looks for the 
satellites in a particular position in the sky but can't find them because 
of a wall or roof blocking its view, then it starts searching the entire 
horizon for all satellites, and even if you then go outside it can take a 
while to find the satellites.

Here is a real example of what I have tried.  I turned on my gps unit 
inside my office, then walked outside and it was taking forever to find any 
satellites.  I turned off the gps receiver turned it back on and within 30 
seconds had a gps fix.

Hope this helps you all understand a bit better why it is important not 
leave/turn on your gps receiver indoors.

Take care and have a great day.
Charles

At 04:54 PM 8/20/2004, you wrote:
>Todd,
>
>There is a sleep mode on the Earthmate but as long as the BrailleNote is
>trying to access it, it won't go to sleep.
>
>If the BrailleNote keeps trying to find a position while inside, the
>receiver seems to lose any indication of where it is in the world. Not sure
>if this is scientifically true.
>
>Mike
>At 08:56 PM 8/19/2004, you wrote:
> >Mike,
> >
> >You told Kim:  "Try not to leave the unit on when indoors.", but why?  A
> >reason for not leaving it on while indoors?  It does not matter if
> >outdoors or indoors because it is just in different environments.  That is
> >why I ask you for specific reasons.  Also, as you know most or all newer
> >equipment nowadays have "sleep" to save battery power, does the GPS have
> >that?  If not, why not add that good feature?
> >
> >Todd

Charles M. La Pierre CTO
Sendero Group, LLC

Lat. 37 15' 25" N  Lon: 121 53' 04" W

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