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

I got mine on 23-12-2010 and came with sw 3.60
I reconverted it to 3790 3.60 now and I must say I get from the window 3 mts accuracy. less satellites shown on display but ,as it has already been told in this thread, more stable bars: bars don't go up and down.
I will update firmware and will make more tests tomorrow outside.

For the record - I bough mine September 10th 2010. It came with SW 2.70 or so.
@ Neil - Unit nuber /not unit ID/ starts like this:1W70xxxxx
As far as I see my unit is the oldest test unit.
Today and tomorrow I'm too busy, but late at night I'll made the same tests and will describe if necessary the process.
Hope that giuseppe66 or Caty will do that before me .

OK, makes sense now. Angelo's info:

Originally Posted by angelozip

....... My 3790 is recent, serial number 381xxxxxxx (sorry, forgot the rest, lol) PCB: V8 8GB 035 DA TC GM. The 3790 of TadFerreira is s/n 380xxxxxxx. .....

But i should have realised that was a UID number not a S/No. My UID for older unit is 380xxxxxxx. My newer unit has 381xxxxxxx.

this morning i've do some test with my nuvi after my procedure. So from my windows, after 4-5 minutes i've 4-5 meters and, very important, blu bars not go up and down. Signal is very stable. In the same place, first, accuracy was about 10 meters.
For me, i think that solution is flash with old 34xx firmware (i've used 3.5) and then update it to new firmware. Before flash i've clean hard disk of nuvi so i don't know if there was a file that decrease accuracy so i can post my files just i've flash nuvi with 3.5
I hope today to do a on route test

[Only registered and activated users can see links. ]


These files are cleaned from my personal information, sorry,
\Logs o \.System\Logs
GarminError.xml
System\diag
GarminDevice.xml
current.gpx,
sqlite,GtmData.xml


This is today, after 1 minute turn on in my car

[Only registered and activated users can see links. ]

so this a solution of poor accuracy (for my nuvi of course) and in post 194 is write what i've do

When I did the conversion I used 3490 3.60 firmware.
I have the common poor accurany problem when watching the satellite screen, but in "real life" I've never encountered any "real" problem.
The satellite bars jump up and down, but I've never had the car jumping to another nearby street, even when I was stationery at a traffic light.

So I've decided to do a different kind of test to check my converted 3760>3490
As I was walking to work today, the sky was 100% clear and I had a perfect view north, east and south with no buildings at all.
On my west side I had 7-story buildings.
I stopped at a corner, got a satellite fix and in seconds it went from ~60m down to 15m accuracy.
Then I turned on Diagnostic Logging Recording (1 point every one second) and here are the results in "real life"
During the 3:40 minutes of the recording, I was standing still at the place on the pavement (blue dot) and keeping time with my phone's timer to check the results later.


1) Accuracy 16~15 m
I seperated the first 40 seconds of the recording and I was surprised to see in Mapsource that even with 15m accuracy, the gpx was indicating my real position.
I could not believe that those 40 gpx points where so close together, almost at the same point, all of them almost at my real position.



2) Accuracy 12~6 m
After those first 40 secconds the accuracy became better and better very fast, and settled down to a stable 6 m.
After 3 minutes (at 6 m most of the time, and never more than 8 m) I turned off the recording.
Back at Mapsource I was again surprised to see that, with better accuracy, my position was not indicated as good as it was above.
Now the 3490 signal was moving around a "box" 11x16 meters.
But even this I find it as very good reception, 180 gpx points, so close together and so close to my real position and for so long (~3 minutes)!!!



From all the above I think that my converted 3760 is very accurate in "real life", even if the indicated accuracy is around 20 or 15 or 10 meters.
My position was correctly indicated in relation with the gpx file I've got.
Accuracy in meters is a probable margin of error in the gps signal.
What I've showed above is that even with "poor" accuracy, the "real" gps fix (recorded gpx points) is extermly close to my real potition.
Accuracy of 15m doesn't necessary means that 3490 indicates my position 15 meters away from the real one.
It means that my real position "could be" within a circle of 15m radius of the gps fix.
The good thing is that, even I was standing still at the same position, the actual points-fixes that 3490 was recording, were very-very close to my real position most of the time, no matter how poor my accuracy was, or how big the blue circle on the screen was.
I don't think that there is a real problem with the gps fix, I think there is a problem with the mathematical calculation of accuracy.

It would be very interesting to have one 3790 and one converted 3490 side-by-side doing Diagnosting Logging for some time.
Then we would compare their gpx files.
What would we say if a 3790 with 4m accuracy and a 3490 with 20m accuracy, at the same place, same time and same weather, gave very similar gpx files...
If both devices gave gpx points very close to our real potition, then "maybe" accuracy is not so important if the "real" fix is always very close to our "real" position.

Just looking at satellites page, 37xx is a way better than 34xx in accuracy. I got better results putting it in the same places where I usually put it to see how it goes:
my bedroom that is in a mansard with wooden roof,
bathroom reinforced concrete roof but with a dormer window ,
my terrace, quite open sky because on the front I have just trees and my terrace is higher and,
tested today, walking in the street and on bycicle.

Results (today completely cloudy sky) :

In the mansard with 34xx I've usually 16/21 mts ,with 37xx :


In the bathroom, not good with 34xx, usually around 40 mts, with 37xx:


From my terrace,: I can get 4 mts with 34xx, with 37xx:


Walking with 34xx from 12 to 20 mts ,it depends on streets, it sometimes looses receptions if building are high.
Walking with 3700 from to 14 mts, not tested with very high buildings today.

Bycicling is quite the same, I havent noticed remarkable differencies than walking.

Driving not tested today, I dont use my car in my city ,too much traffic and no parkings lol.

From what I can understand 37xx reception is not only so better in satellites page, but it can fix satellites where 34xx cant and where you get bad reception message.This is the reason in 34xx with worst accuracy it sometimes jumps your position in a wrong street or it looses completely the reception.
Loly procedure with eph prediction gives a fastest fix and probably increases fixing in bad reception positions, but it cant increase accuracy IMHO if your 34xx has bad accuracy.

The problem is still there in these devices and I guess it will be hard to find a solution.

1) in nuvi 34xx with poor accuracy i've do a copy of all my folder and files on my pc, then i've delete all folders and files not important from nuvi;
2) flash back it to 37xx follow Caty's guide and files [Only registered and activated users can see links. ]
http://www.gpspower.net/attachments/garmin-receivers-firmwares/100811d1350081674-transform-nuvi-37xx-nuvi-34xx-dummies-convert37x34v.zip
3) i've turn on and test accuracy of 37xx with essential files (no map, text, asr, jcv....) and i've good accuracy;
4) then i've flash to 34xx again with firmware 3.50;
5) Caty's solution "convert 37xx34xx.zip" and then Lolypop000's solution "region 139...";
6) backup on pc of "clean folder and files", share on post up;
7) test the accuracy with 3.5 firmware and it's good, like 37xx for me;
7) update with webupdater to firmware 7.6 and other files (voice, asr....);
8) test accuracy and it's good, like firmware 3.5;
9) update with my lifetime, map, asr, jcv.....
10 ) test accuracy like yuo can see in my picture in post up.

For me of course, i've not never see good accuracy on my 37>34 and now yes. Blu bars don't go up and down like "crazy" but now are enaught stable
I don't now exactly if there was a problem with firmware (i've use firmware 7.1 first time i've convert) or a problem with files because i've clean nuvi before flash to 37xx