Ultimate GPS No Fix

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54Oval
 
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Ultimate GPS No Fix

Post by 54Oval »

I just purchased an Ultimate GPS from Adafruit. It communicates fine with my beaglebone, but the message back always shows as Invalid Fix and the light keeps blinking once per second. Even outside on clear night pointed up with only a clean power supply for over a half hour all I get is a ~1hz blinky light.

-Dan

fnj
 
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Re: Ultimate GPS No Fix

Post by fnj »

Believe me, I know about the heartache of GPS.

Have you tried the external antenna? It gives a stronger signal. It seemed to make a big difference for me.

Every once in a while you should be getting a burst of $GPGSV messages - anywhere from 1 to 3 or more in a row. These indicate how many satellites the GPS is receiving. After it has been on for at least 15 minutes, can you post one of these bursts?

You say you tried it outdoors. That is good. But can you describe what it sees overhead? It's not enough just to have a clear view directly overhead. GPS needs a clear view over a good bunch of the half hemisphere overhead. Certainly it doesn't need a perfectly clear view from horizon to horizon in every direction, but it needs a good bit. It can deal with trees to a certain extent, but trees are not good. They attenuate the signal seriously.

If the unit (or the antenna) is outside but near to one wall of the house, it is still getting approximately one half of the usable view blocked. Having said that, with the external antenna sitting inside on a windowsill of a large closed window with NO metal screen fitted, on the south side of the house, I got quite good results. It does take a surprising amount of time to get itself initially oriented, though. At first I had it in a window with a metal screen and couldn't figure why it wasn't getting anything :-)

What is your latitude? Or at least what general location? It is, in very broad terms, generally better for the GPS to have a good view of the general region of the sky nearer the equator than either pole.

54Oval
 
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Re: Ultimate GPS No Fix

Post by 54Oval »

Thanks for the input fnj,

I did not purchase an external antenna. So for the time being I am stuck with the internal one. Using your advice I returned to a large open field tonight for a second trial. For about 15 minutes the only GPGSV message that I got was a single GPGSV,A,1,,,,,,,,,,,,,,,,*1E . From a quick search this seems to indicate a No Fix on any satilites. My ~8 year old GPS from my car had no trouble picking up the signal. I was out in the field for 20 minutes before the mosquitoes were getting the best of me. About to give up I moved to a parking lot where I could hide in the car. After another 5+ minutes in the new location the Adafruit GPS briefly got a fix on 3 satellites. I don't know if something is wrong with my internal antenna, or if this behavior is common with this GPS. BTW, I live just outside Philadelphia My Long/Lat is 39.9167° N, 75.3881° W

-Dan

fnj
 
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Re: Ultimate GPS No Fix

Post by fnj »

Yeah, from what you describe, that doesn't sound good. As a check I removed my antenna to use just the built-in antenna. Sitting on the windowsill indoors and pine trees right nearby outside, within 5 minutes after cold start I had fixes with 3-4 satellites and within 10 minutes I was getting fixes with 6. I'm pretty impressed actually. I'm on Cape Cod (Massachusetts) BTW.

So then I put my Garmin Nuvi 360 right next to the Ultimate on the windowsill and after maybe 5 minutes it said it had a problem and asked me if I was indoors. I lied and said no and it's still straining to get anything.

Is your Ultimate mounted upright with the built-in antenna looking straight up and nothing in the way on top of it (wires, etc)? Don't hate me for checking the obvious possibilities :-)

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adafruit_support_rick
 
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Re: Ultimate GPS No Fix

Post by adafruit_support_rick »

Do you have the backup battery installed? That doesn't power the GPS - it runs the internal RTC. The GPS will pick up a fix faster after a power-on with the RTC running.

As fnj says, make sure there are no wires or other boards obstructing the GPS unit, and that it's pointing straight up.

You also might want to post some pictures of the GPS.

54Oval
 
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Re: Ultimate GPS No Fix

Post by 54Oval »

fnj / Rick

No question is too obvious and I appreciate the experience and input. The unit is installed with no obstructions. I didn't install the battery, and perhaps this will assist with a faster pickup. I guess there is no easy quantitative way of determining if an antenna is performing to spec. Anyhow here are the install images...

Image
Image
Image

fnj
 
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Re: Ultimate GPS No Fix

Post by fnj »

I don't see a thing wrong there. Solder looks OK, the necessary pins are hooked up, nothing seems to be in the way, there doesn't seem to be any foreign conducting material in the antenna jack. The fact that you got one fix indicates it's wired up right. You definitely don't need a battery for the GPS to work as shown by the fact I don't have mine hooked up; the most it can do is make it start operating and getting good fixes faster after the first time, but if you wait 15 minutes with power on this shouldn't be a factor. Maybe make sure to wait 30 minutes once in the open field. Beyond that, I don't really have any more conjecture.

It is theoretically possible to damage the antenna from static just by touching it if you are charged from the carpet. The chance of that happening in the humidity of full summer in the continental US I would judge officially "not bloody likely", but maybe you unpacked it in the extreme dryness of indoors in cold winter. That's almost grasping at straws though.

EDIT - I just checked my setup which has been running for several days with the built-in antenna indoors in the windowsill with lots of pine trees immediately outside. It is getting fixes using 13 satellites! There are only 32 of them in toto worldwide. So that shows you what an outstanding product this is when it's operating properly.

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adafruit_support_rick
 
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Re: Ultimate GPS No Fix

Post by adafruit_support_rick »

I'm with fnj - I can't see anything wrong. Let's just replace it.
Please email [email protected] with a link to this thread and ask for a replacement.

wd6cmu
 
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Re: Ultimate GPS No Fix

Post by wd6cmu »

I've got a similar problem. V3 breakout module, zero satellites captured after 24 hours of sitting in the window. Hooked up the external antenna in the same position the module was in and it locked on to 11 satellites in less than 5 minutes. Bad antenna?

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adafruit_support_rick
 
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Re: Ultimate GPS No Fix

Post by adafruit_support_rick »

wd6cmu wrote:I've got a similar problem. V3 breakout module, zero satellites captured after 24 hours of sitting in the window. Hooked up the external antenna in the same position the module was in and it locked on to 11 satellites in less than 5 minutes. Bad antenna?
Certainly sounds that way. Could be the antenna, or it could be the adapter cable. Are you sure the connections are secure?
Did you get them from us?

wd6cmu
 
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Re: Ultimate GPS No Fix

Post by wd6cmu »

adafruit_support_rick wrote: Certainly sounds that way. Could be the antenna, or it could be the adapter cable. Are you sure the connections are secure?
Did you get them from us?
Um.... The adapter cable and antenna are working fine, it's the patch antenna internal to the module that doesn't see any satellites and I don't think I can check that its connections are secure. The GPS receiver module and adapter cable are from Adafruit, the (working) external antenna is from somewhere else.

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adafruit_support_rick
 
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Re: Ultimate GPS No Fix

Post by adafruit_support_rick »

D'Oh!! Sorry - I read your post backwards. :oops:

Right - so you get fixes with the external antenna, but not with the internal.

First of all, make sure you've got a fresh backup battery installed.

If you get your fixes with the external antenna attached, and then remove the antenna, how many satellites can you see with only the internal antenna?

Or do you lose the fix immediately when you remove the external antenna?

How about if you cycle the power after removing the external antenna?

wd6cmu
 
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Re: Ultimate GPS No Fix

Post by wd6cmu »

adafruit_support_rick wrote:If you get your fixes with the external antenna attached, and then remove the antenna, how many satellites can you see with only the internal antenna?
That was a good test. The number of satellites dropped off (16->14) but it maintained lock, so the built-in antenna is obviously not dead.

Batteries just arrived for the backup power, so I'll try that soon. Thanks.

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adafruit_support_rick
 
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Re: Ultimate GPS No Fix

Post by adafruit_support_rick »

The battery backs up the internal RTC. It will get fixes much faster on power-up with that installed.

wd6cmu
 
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Re: Ultimate GPS No Fix

Post by wd6cmu »

Well, now I'm confused. I was going to install the backup battery when I noticed the receiver was blinking 1/2Hz like it did not have a lock anymore. I looked at the NMEA sentences and got this:

Code: Select all

$GPRMC,054803.019,V,,,,,0.00,90.59,250713,,,N*78
$GPVTG,90.59,T,,M,0.00,N,0.00,K,N*07
$GPGGA,054804.019,,,,,0,0,,,M,,M,,*4D
$GPGSA,A,1,,,,,,,,,,,,,,,*1E
$GPGSV,4,1,13,18,81,342,,21,68,055,,22,53,251,,06,44,302,*71
$GPGSV,4,2,13,15,38,062,,27,34,311,,03,26,312,,16,22,266,*75
$GPGSV,4,3,13,29,19,153,,14,10,187,,19,06,320,,26,04,032,*7C
$GPGSV,4,4,13,24,02,106,*48
The $GPGSV says it's seeing 13 satellites, but the $GPGGA says it has no lock.

I carefully inserted the battery without loosing power, then cycled power to reboot. After reboot it's claiming it still has 12 satellites but no lock. I plugged the external antenna in again, and one minute later I had a lock and a position.

Any guesses what all this means?

Locked
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