APM 2 GPS not getting a lock?

I have been sitting here trying to get a lock with my GPS while outside for about 10 mins.  No luck.  I generally get a lock between 30-60s when outside.  My GPS has worked fine previously.

Other than the CLI test (which only works if I have lock anyway), is there a way to check GPS function?

If my GPS unit turns out to be no longer functioning, what options do I have with the APM2?  Since my GPS is soldered directly to the board, is it possible to get another and use an extension?  I don't trust my soldering abilities enough to remove and replace the current unit

Thanks

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Replies to This Discussion

Permalink Reply by Cala on July 19, 2012 at 4:24am

To have faster lock and no problems whit the ESC

Permalink Reply by Eddie Furey on July 19, 2012 at 6:14am

My GPS worked fine on my "test bench", being my balcony as my unit has a metal roof, but failed to get a lock once installed in my plane. After some testing this evening I found that it received interference from the video cable coming from my FPV camera. So much so that I could get a lock with 5 satellites (not bad for my balcony), put the GPS within an inch of my video camera and it would immediately lose the lock and drop down to 2 sats, then move it to 2 inches away and it would go back to locked with 5 sats within a few seconds.

Needless to say I'm making some alterations to my cockpit layout. :)

Permalink Reply by Dr Mike Black on July 19, 2012 at 12:33pm

hi all,

In my testign today, Eddie, has hit the nail on the head, different results my end though.

In my case its the 900mhz data Tx..

with it off, i get 30% higher sat readings, more sats, quicker locks.

Interesting thing is, with the 200mw 5.8ghz vd tx right up against the GPS no issues at all...60mw Data tx, all drops badly.

Moreover, the only unit it deosnt seem to affect is the ublox with the standard helix antenna, but it affects the patch by the about 15%.

MTK with the 900 on , refuses to lock at all, off, takes 90-180secs, however, the satsare low.

My question is (knowing that we have to keep all tx's as far from the GPs as possible) why is the 900 so prevelent, as far as i know its not a harmonic of the 1.5ghz(ish) GPS....unless of course my personal 900 is getting tired and dirty.

Deos anyone know? Deos anyone have the ability to concure or deny these results?

Either way, this seems to have the most affect on the GPs behaviours so far.

Looking forward to your thoughts.

Kind regards,

Mike.

Permalink Reply by George on July 19, 2012 at 3:58pm

I have a 900mhz low pass filter somewhere, I can try and see if that makes a sat count difference in my set up. Is your 900 data radio one of the 3DR one's Mike? I have my 900 3DR radio within about 3 inches of my MTK and have no issues obtaining a reasonable lock (av 8-10 sats in the air) albeit having solved my dirty power issue's previously. 

Permalink Reply by Jake Stew on July 19, 2012 at 4:56pm

Besides harmonics at multiples of the target frequency there's also "spurs" that are look like this...

The spurs are on either side of the center frequency.

Permalink Reply by Will Snodgrass on July 19, 2012 at 6:07pm

Apparently the onboard GPS can be disabled by bring pin #2 on the gps to ground......Some people are using pin #3 as ground and simply putting a 4k resistor between pin #2 and your choice of grounds. After that you can connect the the ublox without any problems....although the blue light will still light up on the onboard GPS (unless you simply cut the power trace, but it's easier to undo the resistor if you ever want to go back.

Permalink Reply by sebiss07 on July 21, 2012 at 1:10am

Hello,

Do you have a diagram to represent clearly the connections ?

Seb

Permalink Reply by Steven G on July 19, 2012 at 8:01pm

Hi,

I asked earlier but did not get an answer, that is, what is the typical HDOP you all are getting? I finally got my external GPS to get a 3D lock and about 8 sats BUT the HDOP was in triple digits! As I recall HDOP needs to be less than 4 to get reasonable accuracy.

Thanks,

Steven

Permalink Reply by Dr Mike Black on July 20, 2012 at 12:46am

HI all,

So George....your system works as per standard!....this is good....and you can have a 900meg close to the GPS wil no obvious ill effects...

perhaps its something wrong with my personal one?! (I have been trying to buy a 413meg 3dr pretty much since there were released, but seems to be almost alwaysout of stock :(   )

Jake, thanks for the heads up, as to me radio is like a 'white mans magic' i dont understand it, conceptually yes, how it actually works in reality, never got down and dirty with it. more over, i use off the shelf gear, adn the other data rx/tx systems i have are mil-spec for other projects, so not a fair test, (also most of them, will knock out GSM fro about 5 miles once airbourn, which tends to upset the neighbours! So i dont use it out of cleared areas.

My 900 is an old Xbee (probably as old as the MK1 DIYd AP) and had a few muddy/wet moments in its life.

Thanks Will, i will disable the others i have on APM2's instead of ripping them off the board.(y anever know we might get to the bottom of this issue and be able to use them again.

In answer to steven's question, teh mission planner renderes the number differently, HDOP on u-centre will read 1.2 or 3.5 etc, planner read 120 or 350, MTK also works the same way in its set up software you will get 1.2, the moved the decimal place. Best to see the GPS in question direclty on its testing program, thebn correlate the numbers back to the planner, if that helps.

If anyone has an old Xbee and cares to try this, i would be very gratefull for your results.

Kind reagrds,

Mike.

Permalink Reply by Will Snodgrass on July 20, 2012 at 8:39pm

Im not sure If Im missing something in the software, or what. Ive tried on 2 seperate computers to load the latest Firmware and mission planner. Ive left  the unit outside for hours....  Both the built in unit, and now that Ive disabled it the Ublox both blink for a bit then go constant blue....But all I ever get is GPS: No GPS  gpsstatus: 0 along with satcount and the rest...Am I missing something obvious here?

Permalink Reply by Dr Mike Black on July 21, 2012 at 2:20am

Will,

Daft question, but you have blown the ublox-binary code into teh ublox GPS yes? not just left as standard?

No GPS suggests, that the data stream is nto being read, blue suggests that you have a lock.

Sounds to me as though the 2 are not talking the same language.

If you need the code for the GPS i can post it. Use U-Centre to upload the correct code.

Let me know.

Kind regards,

Mike.

Permalink Reply by Will Snodgrass on July 21, 2012 at 2:36pm

Not as bad as trying to get a lock inside a building, but no I haven't uploaded anything to the ublox.... I was going over the instructions on it and and from what I could tell it wasn't necessary on a newer model meant for a copter.....That and I wasnt sure IF I could load the code while it was hooked up to the apm2 or if I needed a special adapter.

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