GPS Issue: Loss of satellites -> Softreset necessary?

[licht77]

Hi!

I encountered a strange GPS behaviour and wanted to share this with you / maybe someone has an idea bout this one:

On a businessjourney i wanted to log my way with my kaiser, and everything went fine so far. But after several hunderts of kilometres, kaiser lost more and more satellites till only 1 was left and the values were unuseable (phantasy-koordinates, speed and altitude too).

I am 100% sure that it was not a problem with our jet or any kind of shielding in it - because after a softreset it could lock again on 8 to 12 satellites. I could approve this strange loss of statellites on longer flights and car etappes (lets say 500km+) now several times.

Any idea what could be the reason?

 

[unwired4]

Did the airline crew know you were using a gps device?

 

[ZorMi]

Did the airline crew know you were using a gps device?

Who cares, GPS device is just a receiver, they use several of them in cockpit. Even GSM mobile phone intereference is exaggerated...

 

[licht77]

Well, since it was our own jet and pilot i guess that its ok

But back to the issue: A friend of mine could acknowledge that he has the same problem when traveling over a certain distance by car.

Is it possible, that this has something to do with QuickGPS where the receiver calculates extimated postitions of the satellites (and those triangulations will be false when moving too far)? Is QuickGPS postition-dependend?

Any ideas highly appreciated...

 

[evilc]

Well, since it was our own jet and pilot i guess that its ok

Good answer

It could be, but quickgps only provides a pre-download of the ephemeris data so that the GPS unit does not have to download it from the satellites. If it does not have the quickgps data, it could download it from the sats (thats why a normal lock takes so long), so I would guess not, unless maybe download of new data from sats is turned off if quickgps is turned on.
I see no option to specify location in quickgps but then again it could look at the handset's country code or something. Surely though it is kilobytes in size at max so downloading the whole world's data via GSM/3G would be no biggie.

On a side note, I get the same issue on my Kaiser even if I stay local sometimes. I *think* it may be getting stuck on A-GPS (Using cell phone masts to get a rough fix) - maybe try and disable A-GPS as it would be no use in a jet?

 

[weasel]

I have experienced the same thing once - and that was after using the Kaiser in a jet for only a few minutes. Once I landed, I started TomTom and was placed over 700 miles from my actual position. A soft rest cured it; I was a bit worried that the high speeds of a jet might have confused/fried my GPS, but all was fine after a soft reset.

 

[licht77]

You may see what I mean here: xxx (username and password: test): Right above Toledo / Madrid the GPS readings go crazy... :-(

 

[chrisnash]

Could this be the mythical 'Barcelona Triangle' ?

 

[RemE]

Interesting, you might try posting this at GPSpassion.com forum. They are the experts in GPS. It's odd that it would loose sats as the view of the sky couldn't be much better and you'd think that it would be able to keep up things, even at jet speeds the number of visible satellites wouldn't change. I would try it with GPS ON and Phone radio OFF as this might rule out any cell tower issues.

 

[licht77]

Interesting, you might try posting this at GPSpassion.com forum. They are the experts in GPS. It's odd that it would loose sats as the view of the sky couldn't be much better and you'd think that it would be able to keep up things, even at jet speeds the number of visible satellites wouldn't change. I would try it with GPS ON and Phone radio OFF as this might rule out any cell tower issues.

Hi! I tried it with GSM off - with no improvement. It seems that this is some kind of bug in the GPS-receiver?

If you have an user in that forum - feel free to post this issue!

Thx, Licht

 

[omega_]

I do experience this problem too. I was thinking it is the problem of the chip, has anyone tried the external antenna and does the problem still persist?

 

[jmat]

Who cares, GPS device is just a receiver, they use several of them in cockpit. Even GSM mobile phone intereference is exaggerated...

Might be exaggerated... but considering how much interference a normal GSM signal has with household electronics (and yes, commercial jetliners are heavily shielded)... it's still kind of scary.

I actually discovered I left my phone on in my bag on a Frontier Airlines flight when the GSM modem started up at around 15,000 feet and the in-seat screen in front of me started flickering and I got that cool 'ch-ch-ch-ch' noise in my headphones.

Whoops.

It's probably safe to have the GPS on, but you really should turn off the radio.. there's no telling what wiring is running next to/under your seat, and there might just be an antenna above your head that you don't know about. It's just not worth the risk (plus, if you get caught.. well.. it's a federal offense).

If you just ask, some pilots will let you turn your GPS unit on in the plane (the flight attendants will ask him/her)... Delta Airlines doesn't seem to have any problem with this, while United and American do.

 

[Farsquidge]

I think you'll find the answer to this thread is to do with the travelling speed and height.

Dedicated flight GPS units have a much faster baud rate for data transfer and the unit itself has virtually no other background tasks to take care of.

The 'Kaiser' GPS is primarily designed as a 'walkabout' unit and can just cope with vehicle speeds. If the data shows a marked change in position (due to say travelling at a few hundred kph) then the GPS firmware believes it has an erroneous sat lock and tries to re-aquire causing the confused output.

Also, Ephemeris data is incorrect for ionospheric distortion when you are at above 25,000 thousand feet so if it tries to use QuickGPS it will actually lengthen the acquisition time.

Try it next time with both A-GPS and QuickGPS off (QuickGPS auto disables if data is out of date so just disable downloads) and note what speed/height you are when is goes crazy.

 

[licht77]

As far as i know, there is no profen evidence that one single plane was downed by a gsm signal. Additionally, i have seen Boeings where all TFT Flatscreens started heavy flickering when the intercom was running - so dont mix up important avionic board systems with unimportant, unshielded secondary systems Here in europe all commercial planes have excellent shielding standards - and there are several commerical and private planetypes around which already come up with internal gsm-repeaters and satellite connections to the gsm-groundstations (the reasons for low usage are missing business models and - i guess annoyance). And - as i said - it was our own jet and pilot, and so its me who makes the rules in there :-D

So much for offtopic.

But I really would like to know what causes this "satellite loss" and "mis-positioning" problems... - this probably makes some killerapplications impossible

Does anybody know if a-gps is geographically influenced? Anybody has further informations about how our Kaisers keep the fix on the satellites?

 

[licht77]

I think you'll find the answer to this thread is to do with the travelling speed and height.

Dedicated flight GPS units have a much faster baud rate for data transfer and the unit itself has virtually no other background tasks to take care of.

The 'Kaiser' GPS is primarily designed as a 'walkabout' unit and can just cope with vehicle speeds. If the data shows a marked change in position (due to say travelling at a few hundred kph) then the GPS firmware believes it has an erroneous sat lock and tries to re-aquire causing the confused output.

Also, Ephemeris data is incorrect for ionospheric distortion when you are at above 25,000 thousand feet so if it tries to use QuickGPS it will actually lengthen the acquisition time.

Try it next time with both A-GPS and QuickGPS off (QuickGPS auto disables if data is out of date so just disable downloads) and note what speed/height you are when is goes crazy.

Thx for your informations - your ideas sound plausible! But on the flight i posted before, u can see that we were travelling about 2.5 hours at 10.000 metres and 800 km/h before everything went crazy within 60 seconds (Placemark 273 is plausible, 275 insane)... but i turned GSM off to save battery... so a-gps and quick-gps should have been off too (correct me if i am wrong)...?

 

[Farsquidge]

Thx for your informations - your ideas sound plausible! But on the flight i posted before, u can see that we were travelling about 2.5 hours at 10.000 metres and 800 km/h before everything went crazy within 60 seconds (Placemark 273 is plausible, 275 insane)... but i turned GSM off to save battery... so a-gps and quick-gps should have been off too (correct me if i am wrong)...?

A-GPS would be disabled but QuickGPS would still be active as it is just a downloaded info table.

It would only need loss of signal for a few seconds, say your reception was detuned by a flight manouver or you moved the location of the unit within the plane (signal strength is poor within an aircraft body without external antenna) to cause it to get confused and at speed it takes ages for a lock. You can see a big difference just starting the GPS standing still against starting it in a moving car.

 

[xconradx]

Consumer GPS devices misread at high speeds and altitudes. Government regulations keep them from functioning to prohibit their use in the construction of ICBM's since most devices use a version of a generic GPS chip. Think I'm nuts? Google it.

 

[Farsquidge]

Consumer GPS devices misread at high speeds and altitudes. Government regulations keep them from functioning to prohibit their use in the construction of ICBM's since most devices use a version of a generic GPS chip. Think I'm nuts? Google it.

Nope, I don't think you are nuts! You are perfectly correct!

There are 3 types, consumer, commercial and military. (four if you count the US who contol the network and have the best).

 

[licht77]

A-GPS would be disabled but QuickGPS would still be active as it is just a downloaded info table.

It would only need loss of signal for a few seconds, say your reception was detuned by a flight manouver or you moved the location of the unit within the plane (signal strength is poor within an aircraft body without external antenna) to cause it to get confused and at speed it takes ages for a lock. You can see a big difference just starting the GPS standing still against starting it in a moving car.

OK I guess i will give this a try as i found out how to deactivate QuickGPS

@xconradx: No youre not nuts - i can confirm that there are regulations (thats why we are gonna send up Gallileo *g*) - but i can hardly believe that this was the bugger: The readings were accurate (too accurate to prevent abuse) for 2:45min - and then the readings were just insane.

I hope we can find a workaround...

 

[xconradx]

Haha, I'm glad people dont think I'm a nutjob... I've tried to explain the regulated GPS to people before and was called "paranoid, crazy", whatever....

Thats weird that it read so well for a period. I just know that basics!