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Legend HCx and satellite information


dunmappin
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I have read numerous times reference to a 'D' appearing in the signal bars on the satellite page of GPSRs if WAAS/EGNOS is enabled. Is this still something that displays? I have 'Normal' mode selected in my Legend setup and WAAS/EGNOS enabled, but have never seen the 'D' as far as I can remember. I am in the United Kingdom.

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I have read numerous times reference to a 'D' appearing in the signal bars on the satellite page of GPSRs if WAAS/EGNOS is enabled. Is this still something that displays? I have 'Normal' mode selected in my Legend setup and WAAS/EGNOS enabled, but have never seen the 'D' as far as I can remember. I am in the United Kingdom.

 

Dunmappin,

 

If I understand it correctly, the WAAS/EGNOS corrections are coming from a combination of satellites and ground stations. The satellites show up on my Legend display (in the US) as numbers 48 and 51, but neither of these satellites is visible from the UK since they got moved a few years ago. Not sure about the ground stations across the pond.

 

Check out this site:

http://gpsinformation.net/exe/waas.html

It gives a lot of background and info on the WAAS system. It looks like they are testing the correction system in Europe right now.

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I have read numerous times reference to a 'D' appearing in the signal bars on the satellite page of GPSRs if WAAS/EGNOS is enabled. Is this still something that displays? I have 'Normal' mode selected in my Legend setup and WAAS/EGNOS enabled, but have never seen the 'D' as far as I can remember. I am in the United Kingdom.

 

You should be able to see EGNOS satellites 33, 39 and 44 or at least those are the ones I occasionally see in Sweden. When the GPS has seen an EGNOS satellite for some time you will get a small "D" on each satellite strenght bar.

 

It works like this... In several places in Europe there are reference stations located at known coordinates. These stations pick up GPS signals and since they know their own coordinates they can calculate the error in the recieved signals. The errors are made into correction data which is transmitted from the EGNOS satellites to your GPS so that your GPS can correct the recieved signals and get a better accurancy.

 

Unlike normal GPS satellites the EGNOS satellites are geostationary (just like TV-broadcast satellites) and that means they are located above the equator. So the further north you are, the less likely it is that your GPS will see them. I live at N60 and I get EGNOS lock now and then but usually only in open areas.

 

WAAS as mentioned above works the same but for North America. And EGNOS recently went "live" and is no longer in testing.

Edited by kallt_kaffe
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With both WAAS and EGNOS, you have to be operating long enough for the GPS to download the correction data. The data is transmitted continuously in one long stream that repeats. The transmission is relatively slow and there is no error correction so if there is an error in the received data your GPS has to wait until the next time it comes around.

 

The correction data is only relevant for "current" conditions so if the GPS has been off for a time (say, a few days), it has to completely acquire new correction data.

 

As has already been stated, the further from the equator you are, the more difficulty your GPS receiver may have acquiring the correction data. Therefore, the longer it may take to get the "differential" (eg. corrected) lock for any of the satellites. (The "D" stands for "differential".)

 

...ken...

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