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

@tom1807

Could you do a test on your 3790? Check accuracy with WAAS/MSAS on and off, and report.

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For others, maybe as unsure as i am about the 'WAAS-type' capabilities of 3xxx:

[First, a Terms explanation in case the several terms are confusing: MSAS is the Asian equivalent of NA's WAAS and EU's EGNOS. All these systems are compatible and collectively called SBAS, the correct (but rarely used) generic term for such systems. That is, a WAAS capable unit receives MSAS and EGNOS and vice versa. I'll just use the term WAAS here, it's easier.]
WAAS was first developed for Aviation, particularly for instrument approaches (non-visual condition) and other precision uses. My opinion is that it's not necessary for safe and normal operation of civilian ground vehicle navigation as we just don't need that 'precision' in a car GPS unit, but i've seen first hand the difference WAAS makes in the air and it could be a 'life or death' difference there.

Ground devices like some Garmins have 'piggy-backed' for a free ride by obtaining the signals from the WAAS sats to increase their accuracy. It's maybe not available to 3xxx units, but i don't know one way or the other.

In regard to the capabilities of WAAS-type systems to minimise error. The ground stations (precisely fixed coordinates) receive data from Sats, compare the sat's info given on the station's location to it's actual location, calculate the error if any, then transmit that back to a sat which rebroadcasts the correction to WAAS capable receivers, but not to non-WAAS receivers of course. So in that sense, in a perfect world with no sat being 'off', the accuracy of a unit with WAAS off would be the same as when it's on, as stated in the info quoted by Caty.

In Post #37 giuseppe66 said his Nuvi 765 EU version has accuracy of 6-7m, however his Nuvi 765 TW version gets 3-4m with WAAS on test at same time. With WAAS off he gets same precision in both. That would seem to indicate that 765 EU has WAAS capabilities because his 765 TW is a convert from EU, not an original.

To settle this, is WAAS available to US/EU 37xx/34xx units? It clearly is available in at least some Nuvi units other than 3xx/6xx. i.e. Tom's 3790TW and (apparently) in giuseppe66's 765 EU>TW convert. The info from Caty is helpful but somewhat dated as she points out. These 3xxx units certainly weren't around in 2008, or even in 2010 were they? Aren't they 2011 and 2012 releases?

The other consideration is how 'truthful' is the accuracy reading on the original US/EU 3790's anyway? Mine seems to always read 3m when there is a clear or only partly cloudy sky. I'm getting suspicious that it actually can constantly maintain that degree of accuracy in practice, even if it is WAAS capable. Is it pre-programmed in the fw to show an artificially 'good' reading?