GPS Diagnostics screen - Help me decipher it

[sna77]

Can anyone clarify what all these abbreviations mean? Just curious what all this is…
Thanks!

[sna77]

I found this wikipedia article and am even more confused now. =0
GPS signals - Wikipedia, the free encyclopedia

[KiwiJochen]

Ch = channel, your GPS can use 8 channels at the same time
S/N = signal to noise, the large the number the stronger the signal
PRN = pseudo-randon code, means satellite number

[sna77]

Thanks Jochen.

PRN appears to be this according to Wikipedia:
pseudorandom noise (also pseudorandom binary sequence) (PN or PRN code)

As far as the Signal to Nosie ratio... The higher the number, the better the signal?

What is considered "good?" On my car, I usually get 7-8 satellites, whereas my wife's car only gets 5-6 (others are 0.0)

[KiwiJochen]

your supplied photo is an excellent example of a GPS antenna in perfect working order.

I've never seen S/N higher than 20
Typical is 3-4 satellites at 10-15 S/N
If all are under 10, something is wrong
And if you only see 0-3 then the antenna is bad

Remember, weather can impact GPS reception.
So take a number of readings over multiple days to determine if antenna is good or bad.

[Terry Kennedy]

Originally Posted by KiwiJochen

Typical is 3-4 satellites at 10-15 S/N

By the way, the MK IV (at least) lies about the number of visible satellites - the number it tells you means it is an 8-channel GPS (some newer receivers - not in the MK IV) are 12-channel.

[big bob]

You need to be on the Nevada Salt Flats with nothing between you and the horizon in every direction to see all 12 satellites. 3 Are needed for a 2D fix, 4-5 for a 3D fix, and after that each satellite reduces the error in the fix and tracking by up to 25%.

What also matters is the number of correlators, you need one for each visible satellite as a minimum. The SiRF Star III had something crazy like 32000 correlators. This allows it to track at 20-30dB below aquisition, ie: indoors, in shipping containers, and in built up areas.

[Terry Kennedy]

Originally Posted by big bob

You need to be on the Nevada Salt Flats with nothing between you and the horizon in every direction to see all 12 satellites. 3 Are needed for a 2D fix, 4-5 for a 3D fix, and after that each satellite reduces the error in the fix and tracking by up to 25%.

Regardless of how many satellites are above the horizon, the MK IV only has 8 channels, so anything more than that is ignored. And it always says 8 are visible. In this picture:



the almanac says that #14 is above the horizon, but there is no signal from it.

[big bob]

Yes, 14 is being tracked by the correlators or is in the Almanac, but has been lost behind a building.