[time-nuts] GPS Modules Indoors

[Bob Camp]

Hi

If "indoors" always includes a view through unshielded windows to towards the equator, then you might be ok. If it includes pole only facing offices in a conventional steel structure - not so much. The issue isn't so much time, as ability to get a good enough signal to lock to. If you add a "unknown" location (you don't have a survey) and an "unknown" almanac (you have been off for a while), that just makes things harder. 

Consider that while I can get cell phone coverage anywhere in my home, there are buildings in the area that I can't get coverage in. Around here, (as in most urban areas), if I can't get a cell phone signal, there's no chance at all of getting GPS. 

Provided you have a valid almanac, a rational location fix (as in a survey), and are tracking multiple satellites, I can't think of a case where you would have a significant time error. That may just be my lack of imagination. 

For one second accuracy, a time tick over a cell phone should be fine. That would be far more robust than a GPS setup.

Bob

On Nov 20, 2012, at 6:33 AM, Tom Harris <celephicus at gmail.com> wrote:

> Greetings
> 
> I know that the accuracy of GPS degrades indoors. However, suppose
> that I just want to turn a GPS module on, acquire the current time
> accurate to a second, and then turn it off. I can get a good deal on
> the U-Blox LEA-5H modules (same as used on Arduino shields I think),
> which have a high sensitivity, and I can use an active antenna if
> needed.
> 
> Am I wasting my time. Sorry for not requiring the time more accurate
> than a second, but that's all the clients require.
> 
> -- 
> 
> Tom Harris <celephicus at gmail.com>
> 
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