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

Originally Posted by Kanopus

If you do a drive test, why don't you register a log?
There exist diagnostic log, start logging in gpx format and then you would be able to analyze real precision of GPS.

Ok, sorry, just i have i post

@Rfb, if you have, can post for me this file? i can't today..thanks

Originally Posted by angelozip

Which software you has used to generate comparative charts and in what situation?

I have used LibreOffice for charts

Seriously: on satellite window long press "Hight" filed and you will find GPS SNR logging window. There you can start logging, in menu "Start CN0 log". At each 10 seconds GPS writes satellite status to a CSV log in \Logs\snr\ or \.System\Logs\snr\. I simple got a good satellite fix at both GPS, put them near window and started logging for 20 minutes.

[Only registered and activated users can see links. ]
This is my log's file. Today i've drive in city (not highs buildings) and today there are clouds. Of course accuracy is not like original 3790 but more better then first (convert directly with firmware 7.10) for me

I have 3790 ->3490 model. Definitely I had accuracy problems and I was happy with new user friendly Garmin software, but in the end of the day I need a reliable and with good accuracy GPS unit. And that is all that matters for me. I knew that many people have that kind of problems, which did not make me happy. One of my friends gave up and went back to 3790 because of the accuracy. I’m not giving up so easy, but without all the participants in the thread I will not be so resistant to the frustration and will to go back to 3790 SW too. In one of my resent trips I have recorded accuracy – if someone is interested I can sent the excel file – but accuracy was awful – in average about + 20 m .

In general the idea of Lolypop000 was do the following:

1st - to reverse SW from 3490 back to 3790.
2nd - to reverse again SW to 3490 not with the last SW available, but with much earlier one – in my case 3.50.
Then to check did html folder [Only registered and activated users can see links. ] and if not to change them.
I have started the procedure for accuracy improvement reading again [Only registered and activated users can see links. ].
My sincere advice to any of you is to read it carefully, does not much matter how experienced in software updates you are. The devil always hides in the details , which are often well forgotten.
Following the instructions I have made copy of the all GPS files to the computer, made copy of region 41, renamed the directories Voices, Text etc., downloaded [Only registered and activated users can see links. ], but it is up to you which to use.
Transformation was successful. I did not put Garmin logo or change directories after 3490->3790 as I needed just accuracy page.
The accuracy was better with 3790 SW. Standing at one place with “clear” sky I had 4 m. accuracy and most important, driving the car I had between 6 and 8 meter accuracy which was perfect.
I have made some screenshots, but unfortunately they disappear in some of my Clear NV or Clear user data…. .
In /.system/GPS/were 3 old files ARC.BIN, BEE.BIN and mt.nvm. In /.system/diag there was no html directory and supported_features file to be checked.
So far, so good.
It was time to go back to 3490 SW. I downloaded [Only registered and activated users can see links. ]. Next time I may try with even lower version and will see did that gives me better results.
Cleared NV, removed GUPDATE if any, flashed the unit.
OK – look like everything was in order. I did not touch dir names, or update something. Again I needed just accuracy.
Accuracy was OK if we talk about standing in one place with a clear view to the sky. Good means good 3-4 meters. Driving tests with 3.50 SW were promising about 4 meters worse accuracy which was let’s say acceptable.
In /.system/GPS/were 3 old files ARC.BIN, BEE.BIN and mt.nvm.
In /.system/diag there was html directory and supported_features file. Both values /see these posts [Only registered and activated users can see links. ] and [Only registered and activated users can see links. ]/ were there and were correct. In my case – same part number and Rev: 0A
I copied rnx folder with all subdirectories sent me by Lolypop000 3490 unit in /.System/GPS – it did not worked for me again. The software did not use them, so after second test I have removed them.
Then I make next step – flashed unit with 3490 SW 7.10. No changes in satellite reception behavior and accuracy.
In the end using myDashboard changed SW to last one 7.60. I have renamed back to normal names all directories, checked and downloaded what I have missed.

Conclusions: Following this procedure you will improve your unit accuracy, but it will not be the same like 37xx one. More or less you will lose accuracy more easy, especially driving and you definitely will need more visible satellites in the sky compared to the number which original 37xx, 34xx or 2xxx will need. In the big cities or in the mountains, in real life the satellites are never enough.
We should try something else.
While waiting I’ll reverse my unit to 3790 and will go with lowest available 3490 SW version.
I’m not expecting miracles but will try. If nothing appears until then, I will transfer the unit to 3790 and will stay with that SW for a one or two week, making some records of the accuracy /snr logs/. Hope that someone will figure out something, because the accuracy is still very important for me.

Maybe we've taken this to the other side.

The question you have to ask yourself, Is the Converted Device Usable for street Navigation or Not ?

Logic Tells Me.

Device is usable for accurate street navigation > Keep it as 3490
Device is not usable for accurate street navigation > Revert to 3790

The Fact that it might show +- 10 meters Accuracy VS 4 Meters Accuracy might just be incidental to the different GPS Chipsets.

Originally Posted by dasilvarsa

Maybe we've taken this to the other side.

The question you have to ask yourself, Is the Converted Device Usable for street Navigation or Not ?

Logic Tells Me.

Device is usable for accurate street navigation > Keep it as 3490
Device is not usable for accurate street navigation > Revert to 3790

The Fact that it might show +- 10 meters Accuracy VS 4 Meters Accuracy might just be incidental to the different GPS Chipsets.

I think that accuracy is important for navigation but it's depending of personal use. Now, accuracy of my 37xx>34xx is more better then first so for me is good. I had problem (with bad accuracy) only in city with highs buildings when nuvi must often do recalculate of route. In city there are many streets very near so gps with bad accuracy don't undestrand where are you exactly and is impossible navigate so. Now that my accuracy is good for me i've not try nuvi in big city. i've decide keep my nuvi with 34xx firmware now because i use also android phone with smartlink and 37xx don't use. I think that another problem of bad accuracy is when we use pedestrian mode because is important in this mode that we have a good accuracy. So, i don't live in a big city and i don't go often in a big city, so for my personal use it's ok