"D" on satellite page, 60CSx?

[snatiep]

Hello Everyone!

 

Every now and then I notice a small "D" in the bars when my 60CSx is locked on to satellites.

 

What exactly does the D mean? Anything to do with WAAS being enabled?

 

Thanks!

Edited August 18, 2008 by snatiep

[+twolpert]

When you have WAAS enabled and you have lock on one of the WAAS satellites, you will see a "D" in the bar for each normal satellite whose data is being corrected through WAAS. Although it would be unusual, it's possible to see a "D" on some satellites but not on others.

[+trainlove]

Although it would be unusual, it's possible to see a "D" on some satellites but not on others.

 

I don't think so.

The firmware in a GPSr will decide on if it should use the WAAS correction, and depending on where a satellite is it may or may not use the corrections for a particular satellite and therefore not show a 'D' for some satellites.

 

On my Magellan Gold I usually get 4 or 5 F's and L's, Fast and Long corrections. But due to the Magellan problems I'll point you to later, I never get any I's Ionospheric correction.

 

Now strangely I've even seen 11 FL's, which is really weird since with 12 channels, and 2 of them being used to see the WAAS satellites, one actually an EGNOS PRN120 and the other not seeing a non-functioning WAAS PRN122), the most that should be seen is 10. Can't replicate that at all though.

 

http://ray.jerome.jobs.googlepages.com/majormagellanproblem

[+twolpert]

Although it would be unusual, it's possible to see a "D" on some satellites but not on others.

 

I don't think so.

The firmware in a GPSr will decide on if it should use the WAAS correction, and depending on where a satellite is it may or may not use the corrections for a particular satellite and therefore not show a 'D' for some satellites.

That was my point, although I may not have stated it clearly enough. The fact that WAAS is enabled and you have lock on a WAAS satellite does not mean the unit will use correction on every satellite. The satellite display on a Garmin receiver does not allow you distinguish among the various types of correction in use. The "D" appears if the receiver is using any type of correction for that particular satellite.

[+EraSeek]

There are three types of WAAS corrections Clock, Ephemeris, and Ionospheric, plus system integrity.

Clock errors change rapidly (I guess this is what you mean by "fast"). Ephemeris ("long?") and Ionospheric conditions are longer lived and Garmin will use those corrections for 2 minutes after losing WAAS, but are in fact good for longer than that, in the order of a couple hours for Ephemeris. In fact Malgellan used to use Ionospheric corrections for up to 45 minutes if I remember right, although I know things have changed at Magellan with WAAS.

 

My former map76 would show "d's" on some but not always all sats. My 60cx almost always shows "d's" on all. I believe the exception is if the unit tries to apply ionopheric corrections to a gps sat that is below the WAAS band mask. This rarely happens, if I am correct on that point.

 

If I recall, the statement that any of these correction brings up the "d's" is incorrect. Certainly at least Ionospheric corrections are the trigger for the "d's" if not all three types together. What I think happens is you need all three to get the "d's" but you will lose it when one drops out (clock most likely) but you will still apply Ephemeris/Ionospheric corrections for 2 minutes after losing full corrections. This is why you may see the "d's" pop in and out more rapidly.

 

Also although there are three types of corrections I believe the corrections are sent Clock/Ephemeris together, and Ionospheric by itself.

 

Likewise Ionospheric corrections are specific to the GPSr's position, and Clock/Ephemeris are not and thus universally applied.

[+JDandDD]

Another reason that the satellite may not have a D is due to the WAAS system providing info or not providing info. The WAAS satellites code each of the GPS satellite as PA, NPA, NM or DNU status. Only a PA status GPS satellite has useable WAAS info. PA stands for Precision Approach, NPA for non-precision appriachm NM for Not monitored and DNU for do not use. DNU means that the GPS satellite is sending unreliable info (right now number 5 is DNU and has been for more than a week).

 

Remember that the WAAS system is by the FAA for aircraft and only sends WAAS correction for those satellites that can be used for a precision landing. So if the GPS is in one of the non-PA modes it will not show a D. Not that the other reasons mentioned are wrong just that this is another one.

 

JD

[+EraSeek]

Yes. Here is a real-time link to that for others to use: http://www.nstb.tc.faa.gov/RT_WaasSatelliteStatus.htm