timcodes

Hi everyone,

Please forgive me if this is in one of the threads but, does someone know what exactly the difference between 12 or 16, or even 21 channel gps?

does anyone have any personal experience of how much accurately the 16 does over the 12 or 21 over the 16?

Is it worth paying for the extra channels?

Thx.

JakeRich

Each channel can listen to one satellite. It takes 4 satellites to get a 3D fix. If you have a WAAS enabled receiver, you need one more for the WAAS data, for a total of 5. Beyond that, additional signals only improve the Dilution of Precision (DOP). Much beyond 7 satellites the DOP changes are small. Right now, with only the USAF satellites in orbit, there are only rarely more than 10 satellites overhead at any time, so 12 channels are sufficient. I've never seen 12 satellites overhead, but I suppose it could happen. Once the EU launches the EGNOS satellites, that number of overhead birds will increase, which may then make higher channel receivers useful, but again, the increase in DOP will be getting smaller and smaller as the number increases.

The real benefit of more satellites is not so much accuracy as it is reliability. If you have exactly 4 satellites and one has a marginal signal, if you lose that you degrade to a 2D fix. With 8 satellites contributing, if you lose one you only see an increase in DOP, not a degradation of fix.

That's about it.

timcodes

Thanks so much!

scgdavis

yeah, thanks! I was wondering about that!!!