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

Originally Posted by Giomen

At next time please make retouch of view in windscreen. In this case I will not be admire a nature and I will see only on sat numbers

It is mean what you receive SBAS ............

HaHA! Very funny g-man. I would think that you freezing northerners should APPRECIATE a view of the great Australian Bush, even on a rainy overcast day. If the sun was out here you'd need your Ray-Bans on just to glance at those photos. But yes, if i see PRN153 or PRN155, (btw, on the Russian forum weren't they talking about 225 not 155 on that guy's etrex?), or for that matter any other sat numbered above 32 again, i will just simply do a screenshot and save my doing any cropping, as there would not be any need to prove that the units were side-by-side contemporaneously in that case ......

All sarcasm aside, i'm pleased to see someone else using the term SBAS. Most ppl i talk to over here look at me strangely if i say that, then when i explain say 'Oh, you mean WAAS!' Now, back On Topic: Yes i know that it means the 3490 was receiving SBAS info, but my question was 'does that mean anything special' in regard to the accuracy problems. i.e. if the 3490 convert was receiving SBAS info but was showing a lesser accuracy than the original 3790 which wasn't getting SBAS, what's that mean when the sig strength reads about 60% for the SBAS sat 153? Shouldn't accuracy be better? Is this the reason some users have 15-20m readings, no SBAS info received?

Also, am i right in believing this?: There are only 32 true GPS sats, with PRNs from 1 to 32 inclusive, therefore any other number displayed by a GPS device is definitely an SBAS transceiver sat? And because it's showing an SBAS sat does that mean it can also use/process the SBAS info, i.e. that it is 'WAAS capable' ?

(Don't beat me up for asking these dumb questions, you're the one with GPS Software Expert after your nick).

Neil!!! Sorry! I was sincerely going to go on pub with you and other man yesterday but as usually I saw a woman's short skirt and walked after her. Be patient - no sex pictures here! Woman's short skirt was a looking for 153 PRN description in Inet source about SBAS, when online searching for satellites in occasional link, at the end it was launching of missile into the carrier rocket that hanging over my house and spying on me (do you see new from Russia about "Зенит-3SL" today?).

OK! Begin from bushes. I often dissemble about my sincere interest to advanced knowledge about GPS devices. Most of my discussion in a raised voice it is nothings for me. It is only workout for the mind! In my settled opinion GPS is means to achieve the other main purpose. The main purpose is locomotion. That is why on first place I have question where Neil is driving, Jesus Christ. And then I think about 37xx converted to 34xx satellites reception accuracy So the great Australian Bush is more attractive for me then photo of MT3351 chipset even on a rainy overcast day.

Well, about workout for the mind actually!

1) I have the belief what geometric dilution of precision (GDOP) is not very objective after I can see number less 15 meters on screen.
http://en.wikipedia.org/wiki/Dilution_of_precision_(GPS)
Too many other factors are trying to challenge that figure. Yes! SBAS must kill this factors by default on right device. But we look a bad DOP (fewer GPS satellites with bad dispersion) on it. Purity of the experiment with digit of accuracy blurred by different quantity and quality of true GPS satellites (not SBAS). But nothing prevents confirm the conclusion what right device (Nuvi 3490) clearly captures fewer GPS satellites.

2) In my case above was EGNOS and not WAAS. I think no difference at all SBAS what present in world. All of them are working on GPS standard signal specification and so WAAS give in device text resource for the sake of brevity.

3) SBAS is good thing! But as mentioned above it have GPS signal specification. Accordingly it works in full measure only with professional device that use several GPS channel simultaneously (L1, L2 and so on). It just gives a some increase in stability on Nuvi but not 100 percent positive result.

Ok, i'm understanding most of that, but i wouldn't have thought that DOP was a problem given the spread of the sats in the pics. The triangulation should be quite good from the spread shown, and in fact that spread was similarly maintained though the entire test run described in Post #29.

So, why does 34x0 convert suffer from accuracy problem especially when moving? If we discount WAAS, DOP, signal strength.. what's left? Fw somewhat incompatible with the 37x0 gps hw on these converted units? Dasivarsa's genuine 3490 gets consistent 3m reading same as my original 3790 (I still think that's not realistic btw, if there is no meaningful WAAS correction how can that accuracy precision be maintained by a 'non-professional' basic gps receiver?).

So Giomen, how about you or Loly or someone please mod 34x0 v7.6 fw with 37x0 gps fw from wotever region it's in, post an *.rgn file and i and any other intrepid souls will flash it to our 34xx converts? Pretty please??

EDIT: Made a reply to the first part of your post also, but a rare flash of good taste and sense led me to decide to delete it after a few hours. However, first i copied it [Only registered and activated users can see links. ] in Aussie Gems if you wanna have a look (you can even reply to it there if you're game!).

Originally Posted by lolypop000

I play with my 3490 and convert it to 3790.
On original 3490 i have 3-5m accuracy, when i convert it to 3790 i have 7-15m accuracy.
Then i convert back to 3490 and still 7-15m accuracy.
Then i go in satellite page and add finger for 5sec on height and set Predicted EPH and cold start.
Turn off nuvi and on again and whait for satellite and after 2 min i have 3m accuracy with 7 satellite bar.

Which would explain perfectly why i didn't notice any difference in accuracy when flashing back and forth between 3790 and 3490 several times.
Do i understand correctly, Loly? You are saying when you convert 37xx to 34xx or back, your unit needs to have those settings checked, be rebooted before satellite fix, and the accuracy problem should be fixed permanently with no need to re-check and reboot each time (unless you reflash)?

Originally Posted by lolypop000

I play with my 3490 and convert it to 3790.
On original 3490 i have 3-5m accuracy, when i convert it to 3790 i have 7-15m accuracy.
Then i convert back to 3490 and still 7-15m accuracy.
Then i go in satellite page and add finger for 5sec on height and set Predicted EPH and cold start.
Turn off nuvi and on again and whait for satellite and after 2 min i have 3m accuracy with 7 satellite bar.

Loly, in personal test I did with 3790/3490 (static mode), there are apparently better accuracy, but I believe that we can only be sure when someone makes a comparative test in dynamic and static mode, side by side, between a 3790 original and a 3790 modified. After this comparitive we can make sure that your method works perfectly, and that's what we all hope. Will have been a great discovery..

In 37xx/34xx if you go to Debugging menu/Developer GPS Tools ,Predictive Ephemeris Age is not active: I mean it doesnt retain settings you set. Even in satellites page even if I check the two you told above, settings are not retained.
Not sure this feature works in 37xx to 34xx.

I convert 34xx to 37xx and then back

I try all that i think of but i have accuracy 7-15m ( before 3-5), then i see this settings for Predicted EPH and cold start.
I set this settings but no difference when i have satellite lock.
Then i turn off and back on nuvi and go to satellite page and whait for satellite lock.
First was 133m accuracy then go down to 3-5m.
I again turn off and back on nuvi and go to satellite page and after 10 sec i have 3-5m accuracy
Every time when i start nuvi i have now 3-5m like before flashing.

So this is procedure:
Go to height page and set Predicted EPH and cold start (you set this only one time)
Go to satellite page and whait for satellite lock
Turn off and then again on your nuvi.
Go to satellite page and whait for satellite lock (after 1-2 min you will have 3-5m accuracy)
Turn off and then again on nuvi and you will have satellite lock in about 10sec with 3-5m accuracy

When you again convert nuvi to 37xx or to 34xx, then you must use again above procedure, but if you flash 37xx to 34xx and you stay on 34xx then you do this only one time.

p.s.
I have Pc beside window and have 3-5m accuracy in my room
I don't know if i have only luck, but this procedure work for me, i hope that will work also for other people.