What are the D's for

[+Raven02]

First let me say I have the 60csx. I can see Sat #51 and I have D's in all the rest of the Sat's. What exactly are the D's for. Do they stand for something? Also is -/+ 11 feet good, bad, average?

 

Thanks.

[John E Cache]

First let me say I have the 60csx. I can see Sat #51 and I have D's in all the rest of the Sat's. What exactly are the D's for. Do they stand for something? Also is -/+ 11 feet good, bad, average?

 

Thanks.

My guess is Differential as in Differential GPS or DGPS.

[+EraSeek]

WAAS sat 51 is applying corrections to the GPS sats, which corrects timing and position errors caused by things like an active ionosphere. Yes, 11' is pretty good, but that figure is just a programed estimate.

[+Sputnik 57]

The 'D' stands for timing differential. This means you received a timing differential update on that specific satellite. The GPSRs typically only receive this update through a signal sent from the WAAS satellites. WAAS Satellites are any satellite you are receiving with a number of 33 or higher.

In my experience, 11 feet has no meaning in the physical world. It is only an indication of relative accuracy for your unit. In other words, if your EPE was 27' yesterday, and 7' the day before, 11' means that you are getting a pretty good signal. I don't think I've ever seen and EPE on my unit below 7' (I have a 60C), and it has sometimes been as high as 190' (on an airplane). So in my mind, it is sort of like saying, "how is my unit doing today on a scale of 1 to 100?" For my unit, 11' is pretty good. Also based upon my experience, if my 60C says 11' and my partner's says 19', I can't necessarily say that my unit is more accurate than theirs. I use it only to compare the current reading to the reading at other times on my unit.

[flfirefighter]

The 'D' stands for timing differential. This means you received a timing differential update on that specific satellite. The GPSRs typically only receive this update through a signal sent from the WAAS satellites. WAAS Satellites are any satellite you are receiving with a number of 33 or higher.

In my experience, 11 feet has no meaning in the physical world. It is only an indication of relative accuracy for your unit. In other words, if your EPE was 27' yesterday, and 7' the day before, 11' means that you are getting a pretty good signal. I don't think I've ever seen and EPE on my unit below 7' (I have a 60C), and it has sometimes been as high as 190' (on an airplane). So in my mind, it is sort of like saying, "how is my unit doing today on a scale of 1 to 100?" For my unit, 11' is pretty good. Also based upon my experience, if my 60C says 11' and my partner's says 19', I can't necessarily say that my unit is more accurate than theirs. I use it only to compare the current reading to the reading at other times on my unit.

 

If you only get D's on WASS sats and WASS sats are #33 and above, why do we get D's on all sats below 33 also? Just curious here.......

[Iwuzere]

D on other channels shows that the differential adjustments have been applied to each channel.

 

[flfirefighter]

D on other channels shows that the differential adjustments have been applied to each channel.

 

 

But the above statements says you only recieve D's on WASS sats? Also, why one would reseive D's across the board and not on 51?

[+Red90]

The "D" indicates that WAAS (or differential) corrections are being applied to that satellite signal. The corrections come from the WAAS satellites and are applied to all "ranging" satellites. At the moment, satellite "51" is NOT sending ranging signals. Normally WAAS satellites send ranging as well as correction signals. Howver, 51 is still in test and has not been set up to send ranging signals.

[beauxp]

WAAS sat 51 is applying corrections to the GPS sats, which corrects timing and position errors caused by things like an active ionosphere. Yes, 11' is pretty good, but that figure is just a programed estimate.

 

EraSeek is correct. You are getting WAAS info and 11 is very good. I usually average about 15 to 20 on my same unit

[ossumguywill]

The 'D' stands for timing differential. This means you received a timing differential update on that specific satellite. The GPSRs typically only receive this update through a signal sent from the WAAS satellites. WAAS Satellites are any satellite you are receiving with a number of 33 or higher.

In my experience, 11 feet has no meaning in the physical world. It is only an indication of relative accuracy for your unit. In other words, if your EPE was 27' yesterday, and 7' the day before, 11' means that you are getting a pretty good signal. I don't think I've ever seen and EPE on my unit below 7' (I have a 60C), and it has sometimes been as high as 190' (on an airplane). So in my mind, it is sort of like saying, "how is my unit doing today on a scale of 1 to 100?" For my unit, 11' is pretty good. Also based upon my experience, if my 60C says 11' and my partner's says 19', I can't necessarily say that my unit is more accurate than theirs. I use it only to compare the current reading to the reading at other times on my unit.

 

If you only get D's on WASS sats and WASS sats are #33 and above, why do we get D's on all sats below 33 also? Just curious here.......

What D means is that WAAS sattelites are giving you a corection message for that sat. WAAS tells you if there is any disterbance in the ionoshpere and tells your gpsr how to correct it.

[ossumguywill]

WAAS sat 51 is applying corrections to the GPS sats, which corrects timing and position errors caused by things like an active ionosphere. Yes, 11' is pretty good, but that figure is just a programed estimate.

 

EraSeek is correct. You are getting WAAS info and 11 is very good. I usually average about 15 to 20 on my same unit

Just to make sure everyone knows, if it says 11 feet accuracy does'nt mean it's 11 feet wrong, it means it could be up to 11 feet off.

[DogFleazJR]

Just to make sure everyone knows, if it says 11 feet accuracy does'nt mean it's 11 feet wrong, it means it could be up to 11 feet off.

 

I believe Garmin units report a confidence interval - there is 95% probability that your true location is within the reported radius.

 

There is a 5% probability that you are someplace else altogether. Freaky.

 

I agree with Sputnik - it is a relative measure and not absolute. My ol' GPS V will report accuracies of +/- 6 ft (with clear view of the sky), where as my 60CSx has never dropped below 9 ft (this was in Kansas) and 11-15 is typical in the car here in NJ. From experience, I have more confidence in the 60CSx even with the lower reported accuracy

[itchytweed]

I had asked this question to Garmin about what the distance is: either +/- 7 ft or +/- 3.5 ft. The answer was +/- 7. Well, 7ft is about 2 meters. Given what is being done and the instability of the whole system (crystal oscillators, mother nature, ionosphere, how many boo-boo's are on your hands, etc.), I'll take +/- 7 feet.

 

Of course, the more direct the correction signal is, the more accurate the corrections can be. Right now, we are at solar minimum. I would seriously doubt consistent locations at solar max when the ionosphere is doing fits, splits, and handsprings.

 

Since the GPSr is lining up data signals to get position, one could use the jitter to determine confidence. A lot of jitter would be a poor fix and little to no jitter would be great.

 

Since I can remote my antenna, me thinks I will put a monument in my front yard. Run the GPSr with its lights on to keep it warm and inside and do several six hour runs at the same location. This will be fun since I can see all three WAAS birds.

 

Also, it looks like two more days and 48 goes live....