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 > How does GPS work?

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2oldman

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Posted: 02/16/22 11:02am Link  |  Quote  |  Print  |  Notify Moderator

ktmrfs wrote:

the more sat's it can access the faster and more accurate you'll get a good "fix".

And yes, my units are usually off during traveling when not needed and it can often take 5 minutes or more to get a good location fix, especially on smaller handheld units.
I read somewhere it usually needs 4 at a minimum.

My stupid Garmin can take upwards of 15 minutes to get a fix, and then I often hear "lost satellite signal." If cell service is available google maps is much better.

ktmrfs

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Posted: 02/16/22 01:39pm Link  |  Quote  |  Print  |  Notify Moderator

2oldman wrote:

ktmrfs wrote:

the more sat's it can access the faster and more accurate you'll get a good "fix".

And yes, my units are usually off during traveling when not needed and it can often take 5 minutes or more to get a good location fix, especially on smaller handheld units.
I read somewhere it usually needs 4 at a minimum.

My stupid Garmin can take upwards of 15 minutes to get a fix, and then I often hear "lost satellite signal." If cell service is available google maps is much better.


needs 4 or more to get accurate location accounting for elevation and determining elevation, My understanding is In a pinch 3 will get reasonable location, but with limited accuracy. with 3 sat's it assumes you are on a flat location at mean sea level.

So for 3 dimensional location (latitude, longtitude and elevation) 4 sat's are needed at a minimum.

if you are moving much above a walking speed, I think it also needs another sat to determine velocity and take into account time and frequency shifts


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cleo43

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Posted: 02/16/22 04:22pm Link  |  Quote  |  Print  |  Notify Moderator

2oldman wrote:


My stupid Garmin can take upwards of 15 minutes to get a fix, and then I often hear "lost satellite signal." If cell service is available google maps is much better.

It's sad to see companies, who were pioneer in their field, that refuse to keep up with advance of technology - then get clobbered in modern time. The day that people, especially young ones, waiting forever for a Position Fix is over.

Matt_Colie

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Posted: 02/16/22 06:22pm Link  |  Quote  |  Print  |  Notify Moderator

2oldman wrote:

I read somewhere it usually needs 4 at a minimum.

My stupid Garmin can take upwards of 15 minutes to get a fix, and then I often hear "lost satellite signal." If cell service is available google maps is much better.


Well Oldman,
I believe you have a unit that has either a bad antenna or has never been updated. My oldest sitting next to me has acquired three satellites since I started typing. That is a 20yo 48.

I have been lots of places where there was a single cell tower and the handset did not have a real GPS (most do now) and Google maps was lost and useless and I had not even over driven the loaded map yet.

Matt


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ktmrfs

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Posted: 02/16/22 06:57pm Link  |  Quote  |  Print  |  Notify Moderator

garmin inreach for gps AND duplex sms capability with iridium sat system and emergency extraction if needed. All I need in one unit.
I just turn the unit on at least 10 minutes before we leave. If i'm near the location I turned it off at, get GPS in a minute or less. Going from PNW and then turning it on in south america... 10 minutes for a fix.

valhalla360

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Posted: 02/16/22 08:08pm Link  |  Quote  |  Print  |  Notify Moderator

2oldman wrote:

My stupid Garmin can take upwards of 15 minutes to get a fix, and then I often hear "lost satellite signal." If cell service is available google maps is much better.


15 minutes is a little extreme even for the older dumb units but if the antenna is positioned such that it can't see a significant portion of the sky, it may have difficulty finding enough satellites.

Keep in mind if you have a cluster of 6 satellites in a small section of the sky, it will still struggle to get a good fix. You want them well distributed across the sky for best results.

Phone based GPS has an advantage that it can use cell tower locations to jump start the process.


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