12 Channel Parallel Receiver +waas/egnos

[Simcoe]

I was wondering, I see some units claim to have 14 and even 16 channel receivers, plus WAAS and EGNOS capable, but is there really a reason to have more than 12 plus WAAS/EGNOS? If 24 GPS satellites make up the system (not including spares), then really in theory only half of them should have a line of sight with any one position on the Earth's surface at any given time, right!? Unless they are not equally positioned, but I thought they would be.

Or are the 14 channel receivers, just 12 GPS plus 2 WAAS?

[+Airmapper]

Given the GPS only will actually use 4-5 of them at any given time, more channels are not completely necessary, it just means it has access to more when it needs to start tracking a different satellite.

 

WAAS and a good antenna, and from what I hear, SIRF will improve signal quality, but 12 channels is adequate. More channels do not necessarily mean better performance.

[+fizzymagic]

Given the GPS only will actually use 4-5 of them at any given time...

I don't know what kind of GPS you have, but mine typically uses 7-9 for the position fix when I have a good view of the sky. Maybe the company that makes your unit doesn't understand enough math to do overdetermined solutions?

[+Airmapper]

I'm no expert, and don't claim to be, but the way I understood it, 4-5 satellites with the strongest signals are used for the position calculations, and the rest were used as needed. My unit will "lock" on every sattellite that is not obstructed. But of course I could be mistaken, and if I am I welcome clarification.

[+EraSeek]

IOr are the 14 channel receivers, just 12 GPS plus 2 WAAS?

 

Yes. According to the article from the chip maker in GPS World, that is pretty much what it is. 2 dedicated channels for WAAS.

[+GPSlug]

I'm no expert, and don't claim to be, but the way I understood it, 4-5 satellites with the strongest signals are used for the position calculations, and the rest were used as needed. My unit will "lock" on every sattellite that is not obstructed. But of course I could be mistaken, and if I am I welcome clarification.

Nope. A GPSr will use a least squares or Kalman filter solution using all of the satellites it can. The higher/stronger satellites will be weighted more though.

 

Back to the OP. There will sometimes be more than 12 sats visible, but the added geometry going from 12 to, say, 14 is going to be a pretty small improvement. What additional channels will get you, though, is that when you are in a heavily obstructed environment (e.g. downtown "urban canyon"), each channel will be ready to pick up its signal for the brief glimpses it's available. Still this is a pretty small effect since those 13th and 14th satellites are likely down in the dirt. But it will eventually be very useful if you have your 36 channel GPS/Glonass/Galileo handheld really searching "all in view". Can you wait 5-10 years for the satellites to be up and for it to be affordable though?

[+HaLiJuSaPa]

I'm no expert, and don't claim to be, but the way I understood it, 4-5 satellites with the strongest signals are used for the position calculations, and the rest were used as needed. My unit will "lock" on every sattellite that is not obstructed. But of course I could be mistaken, and if I am I welcome clarification.

Nope. A GPSr will use a least squares or Kalman filter solution using all of the satellites it can. The higher/stronger satellites will be weighted more though.

 

Back to the OP. There will sometimes be more than 12 sats visible, but the added geometry going from 12 to, say, 14 is going to be a pretty small improvement. What additional channels will get you, though, is that when you are in a heavily obstructed environment (e.g. downtown "urban canyon"), each channel will be ready to pick up its signal for the brief glimpses it's available. Still this is a pretty small effect since those 13th and 14th satellites are likely down in the dirt. But it will eventually be very useful if you have your 36 channel GPS/Glonass/Galileo handheld really searching "all in view". Can you wait 5-10 years for the satellites to be up and for it to be affordable though?

 

I know some Magellans advertise 14 satellites and this takes into account the WAAS mentioned in an earlier post by someone. The only two units I know of that advertise more than 14 satellites are the Lowrance IFinder GO series (16) and the old Cobra 100 and 500 (18). I think these were just marketing ploys to get your attention. While the IFinder GO has great reception, the 18-satellite capability does nothing for the old Cobras, they actually have probably the poorest performance of any GPSr out there and their 1000 model (which "only" tracks 12) performs better.

 

If our gov't ever has more than 24 satellites up there, a unit tracking 14 or 16 or 18 might do better, but it won't do anything for GLONASS or (eventually) Galileo as they will be on different frequencies that these units are not tuned to receive. I'm sure when/if Galileo is up and running in a few years you'll find someone out there come out with a unit that will track both sets of birds.

Edited March 19, 2006 by hairymon

[+jotne]

The new SiRF III ship that Garmin uses in 60Cx and other, has capability to handle 20 channels, but Garmin has only used 12 of them. You do not need more today.

[+EScout]

The few times my eXplorist reported receiving 14 sats, I counted the sats in the constellation screen and I counted 12 plus two Ws. In the signal strength area, it shows 12 spaces, although when less than 12 regulars are receivable, I have seen a W in this area.