Thread: About 37xx converted to 34xx satellites reception accuracy

Originally Posted by Astx

i have a problem with 3790->34хх
HardwareVersion: V8 8GB O35 DA TC GM

What is the problem ?
You need to explain fully.

I think Astx is saying that he has the (inaccuracy) problem with his 3790 converted to 3490, and is letting us know his about his hw. It's the EU V8 8GB. My 3790>3490 is the US V8 2GB.

Really the difference between the 3790 original and modified is not as worrisome, but it could not exist. The question is "academic" and practice: understanding the exact cause and later finding a solution. It would be perfect to have the 3790 modified with the same level of precision of the original. I don't believe that the WAAS has direct link with mentioned problems. These models do not have WAAS / EGNOS available possibly because your level of accuracy is more than needed for civilian and road use (good hardware and sophisticated algorithms correction). I hope to have time in the next days to do some experiments, nothing like practical and methodical testing to confirm, whether or not, our views and hypotheses ..

Originally Posted by Neil

....... WAAS is used as an acronym internationally, and ..... I think it's more correctly called SBAS (Space/Satellite Based Augmentation System) internationally and I also think it's normally enabled by default in most modern units ......
This is just another 'hypothesis' of mine. Ready to be shot down in flames by the Software Experts ......

Originally Posted by voyager56

........... In new models there is no such feature like turning on/off WAAS/EGNOS. Maybe because now WAAS/EGNOS is widely available.......

Originally Posted by angelozip

....... I don't believe that the WAAS has direct link with mentioned problems. These models do not have WAAS / EGNOS available possibly because your level of accuracy is more than needed for civilian and road use (good hardware and sophisticated algorithms correction). I hope to have time in the next days to do some experiments, nothing like practical and methodical testing to confirm, whether or not, our views and hypotheses ..

Originally Posted by voyager56

I think the latest models are able to decide to use not WAAS/EGNOS. So there is no need to have an option selectable by user.

Which is it guys? I was guessing that WAAS is enabled by default in modern units and not de-selectable.
Voyager thinks latest models are smart enough to decide whether to use it or not, so in that sense it's not user selectable/de-selectable.
Angelo is stating that these models don't use WAAS because it's not available to them.

Which is it, definitively? WAAS capable, or not? If they don't use WAAS at all obviously the problem is elsewhere.

In one sense, i believe this is a 'storm in a teacup' because accuracies up to 15m really are acceptable for civilian road navigation. We are wanting 3-4 metre accuracy. ILS systems for precision aircraft approaches require 4 metres or less. That sort of puts it in perspective. It means converted units like mine, voyages and caty's getting 3-10m are quite acceptable. But ppl getting 15-20m need a solution imo.

Look here

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And:
Without WAAS your calculated position will be accurate to within 15 meters 95% of the time. With WAAS your calculated position will be accurate to within 5 meters (I think 3 is a stretch) 95% of the time.

So without WAAS that doesn't mean you are only getting 15 meter accuracy. 95% of the time it will be better than that. So the difference between them can't be calculated as 12 meters (15-3).

The road network isn't mapped with that degree of accuracy, so thinking back to high school math class regarding precision, the accuracy of the GPS/map combo is only as strong as the weakest link... in this case the underlying map.

You will never notice the difference driving down the road if WAAS is available and turned on, versus it being turned off-- with the exception that your battery will drain faster with WAAS on.

Even at a slow speed of 25mph the difference (12 meters) goes by in about one second. The refresh rate of the map screen is typically about one second.

So the difference between WAAS and no WAAS in a car is irrelevant.

And again:

Something else about WAAS that is worth mentioning... The GPS satellites are supposed to travel in their designated orbits. Sometimes they can be a little "off" from where they are supposed to be. The WAAS system calculates how much they are off, and provides correction information to your GPS.

So if all of the satellites were exactly where they are supposed to be, no correction information would need to be applied. Therefore your position wouldn't be any different, WAAS or no WAAS. Of course that doesn't happen and correction information does help, but depending on how far "out" things are, the satellites you are connected to, etc the benefit won't always be significant.

from:

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This is pretty old but is from Garmin support:
Is my Garmin nuvi compatible with WAAS/EGNOS?
12/17/2010

If you have a Garmin nuvi 300 or 600 series device you will have the option to enable WAAS/EGNOS. Enabling WAAS/EGNOS on your nuvi 300 or 600 series unit may improve the accuracy to less than three meters on average.

To enable WAAS/EGNOS on your nuvi:
1.Power the nuvi on

2.Touch on the Spanner/Wrench icon from the main menu screen

3.Touch System

4.Touch Off next to WAAS/EGNOS

5.Touch On

6.Touch OK


WAAS/EGNOS will now be enabled on your device.


Note: Only the nuvi 300 and 600 series have the WAAS feature. All other nuvi models contain a high-sensitive GPS receiver that does not require the WAAS feature.

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