GPS Problems

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See GPS for details on how to evaluate the Freerunner GPS with command line utilities.


Problems I'm having with the GPS
Username Checked outside? External antenna? Note
Pthorin Yes No I tried for about 40 minutes outside, I'm running om-gta02 P1-Snapshot-20080622. Did get GPS time outside, but only got lines like:

$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99*30

--Pthorin 05:11, 11 July 2008 (UTC) I tried it out once again after removing the front cover and got a fix quite fast, less than five minutes. Could there be an issue with the case blocking the signals? Could the snap/latch above the antenna be a problem?

iandouglas Yes No Spent over a half hour outdoors, the NMEA port on my Samsung Blackjack 2 found my position just fine, but also got the same 99.99,99.99,99.99*30 line as Pthorin when powering on the GPS unit, starting gpsd, then running gpspipe at the command line
genki Yes Yes Same here. Does not get a fix without external antenna. GPS output is 99.99,99.99,99.99*30 as well
timo Yes No Spent over a half hour outdoors in an open area without nearby buildings. Zero good fixes, no time gotten, GPS output scrolled along with same numbers for the whole time. When I played some more, very rarely I noticed that in the AZ tab a satellite blob had appeared, always at 0 degrees at the top of the picture. But still no fixes at all or anything. Update: Was able to get a fix in (completely) another location. Looks like the signal may be non-existent in many situations even in seemingly very open places, and together with the shaky software it may be sometimes really hard to say if there is a hw problem...
Ole Yes Yes Tried 15min outside w/o external antenna. Did not get any activity on the SS tab. With external antenna from my window TTFS 33s.
Adsllc Yes No Tried 15min outside last night. Got UTC time and a couple of satellites on the SS tab, but no fix. Reseated the GPS connector, still had no luck. This morning I set it outside, did other stuff for 30 mins or so, then came back to see a successful fix and all tabs in the OM AGPS UI app working. Worked fine on a trip to the post office. Tried again later, no joy.
Dummy ?  ?

Contents

Solved problems

Let's collect hints which could solve the above problems here. E.g.: How to get the best results with your internal antenna

Basic GPS debugging

It could be that your GPS device is functioning properly, but needs to be "coaxed" into getting an initial fix.

  • Before reporting a problem here, please check that you've had the GPS out in the open air, preferably with the GPS antenna pointed up for over 15 mins. (the screen the right way up, with the top of the phone facing up, and the screen facing the horizon). This should get a lock in even the worst cases.
  • However, you might not obtain a lock if the orientation or position of your phone continuously changes. It needs to be stationary long enough to download a frame of data from one of the satellites. Frames are 1500 bits and take 30 seconds to broadcast. The first 6 seconds of the frame contains clock data; the remainder describes the satellite position. Downloading this data can take a surprisingly long time for two reasons.
    1. The GPS reception is sensitive to the orientation of the phone. When you move the phone, it can corrupt part of the current frame.
    2. GPS signals reflect off buildings, interfering with reception in seemingly random ways. If local objects cause signal reflections between you and the satellites, the data may repeatedly fail to download; try facing a different direction (and then holding still) after a few minutes without a lock.
  • Is your unit obtaining signal at all? Check using the AGPS test program "Openmoko AGPS UI". Click "Power On" to begin the test.
    • The "ss" button lists satellites and signal strengths; pressing the "dBm" or "C/N0" button at the bottom of the screen cycles through different scales; a signal between 130dBM and 150dBm should be adequate for a lock, assuming the Neo obtains a consistent signal (lower numbers / taller bars are better).
    • It may take a few minutes for the first satellite to appear in this display. You'll need multiple satellite signals to get a lock.
    • Before getting a lock, the "UTC" field in the "run" tab should start displaying the current time. This value is obtained via the GPS antenna; it may take a few minutes for this field to become populated.

Finally, there is probably room for improvement in the way GPS fixes are currently obtained. GPS devices can obtain fixes at least three different ways. The least sophisticated method downloads a set of current satellite orbits by downloading frames. If part of a frame is corrupted, the GPS device must wait 30 seconds for it to be retransmitted.

A slightly more sophisticated approach uses an initial estimate of the current time and your position to obtain a lock more quickly. Finally, instead of downloading orbit and position data from the satellites, some modern GPS devices simply recalculate the information locally. Some (or all?) of these optimizations are supported by the Freerunner's GPS device, though the software installed at the factory does not seem to make use of them.

More Info to get a fix

I'd like to stress what is written above, it really helped. I put my FR on a table outside, standing vertically with something to hold it upright, switched to the SS display, clicked the db button, waited about 2 mins to get a bar, then turned it around its vertical axis slowly watching the bar go up and down. When it was facing the right way for a maximum bar length I left it like this, without touching it for about 10 mins, and it was able to find the other satellites and get a fix. It is important to not touch it or move it once it gets the first satellite. However it did lock up solid after about 30 minutes, and power button did not reset, needed to remove the battery which of course lost the fix.

Information about faulty antennas

  • If you list your problems above, note if you've tried unplugging and replugging the internal GPS connector. (See Disassembling_Neo1973 about 2/3 of the way down. (this may differ on freerunner, pictures appreciated)

FreeRunner_GPS_antenna_repair_SOP Indicates that the problem may be bad soldering, and includes a guide to fix. This will presumably void your warranty.

Personal tools

See GPS for details on how to evaluate the Freerunner GPS with command line utilities.


Problems I'm having with the GPS
Username Checked outside? External antenna? Note
Pthorin Yes No I tried for about 40 minutes outside, I'm running om-gta02 P1-Snapshot-20080622. Did get GPS time outside, but only got lines like:

$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99*30

--Pthorin 05:11, 11 July 2008 (UTC) I tried it out once again after removing the front cover and got a fix quite fast, less than five minutes. Could there be an issue with the case blocking the signals? Could the snap/latch above the antenna be a problem?

iandouglas Yes No Spent over a half hour outdoors, the NMEA port on my Samsung Blackjack 2 found my position just fine, but also got the same 99.99,99.99,99.99*30 line as Pthorin when powering on the GPS unit, starting gpsd, then running gpspipe at the command line
genki Yes Yes Same here. Does not get a fix without external antenna. GPS output is 99.99,99.99,99.99*30 as well
timo Yes No Spent over a half hour outdoors in an open area without nearby buildings. Zero good fixes, no time gotten, GPS output scrolled along with same numbers for the whole time. When I played some more, very rarely I noticed that in the AZ tab a satellite blob had appeared, always at 0 degrees at the top of the picture. But still no fixes at all or anything. Update: Was able to get a fix in (completely) another location. Looks like the signal may be non-existent in many situations even in seemingly very open places, and together with the shaky software it may be sometimes really hard to say if there is a hw problem...
Ole Yes Yes Tried 15min outside w/o external antenna. Did not get any activity on the SS tab. With external antenna from my window TTFS 33s.
Adsllc Yes No Tried 15min outside last night. Got UTC time and a couple of satellites on the SS tab, but no fix. Reseated the GPS connector, still had no luck. This morning I set it outside, did other stuff for 30 mins or so, then came back to see a successful fix and all tabs in the OM AGPS UI app working. Worked fine on a trip to the post office. Tried again later, no joy.
Dummy ?  ?

Solved problems

Let's collect hints which could solve the above problems here. E.g.: How to get the best results with your internal antenna

Basic GPS debugging

It could be that your GPS device is functioning properly, but needs to be "coaxed" into getting an initial fix.

  • Before reporting a problem here, please check that you've had the GPS out in the open air, preferably with the GPS antenna pointed up for over 15 mins. (the screen the right way up, with the top of the phone facing up, and the screen facing the horizon). This should get a lock in even the worst cases.
  • However, you might not obtain a lock if the orientation or position of your phone continuously changes. It needs to be stationary long enough to download a frame of data from one of the satellites. Frames are 1500 bits and take 30 seconds to broadcast. The first 6 seconds of the frame contains clock data; the remainder describes the satellite position. Downloading this data can take a surprisingly long time for two reasons.
    1. The GPS reception is sensitive to the orientation of the phone. When you move the phone, it can corrupt part of the current frame.
    2. GPS signals reflect off buildings, interfering with reception in seemingly random ways. If local objects cause signal reflections between you and the satellites, the data may repeatedly fail to download; try facing a different direction (and then holding still) after a few minutes without a lock.
  • Is your unit obtaining signal at all? Check using the AGPS test program "Openmoko AGPS UI". Click "Power On" to begin the test.
    • The "ss" button lists satellites and signal strengths; pressing the "dBm" or "C/N0" button at the bottom of the screen cycles through different scales; a signal between 130dBM and 150dBm should be adequate for a lock, assuming the Neo obtains a consistent signal (lower numbers / taller bars are better).
    • It may take a few minutes for the first satellite to appear in this display. You'll need multiple satellite signals to get a lock.
    • Before getting a lock, the "UTC" field in the "run" tab should start displaying the current time. This value is obtained via the GPS antenna; it may take a few minutes for this field to become populated.

Finally, there is probably room for improvement in the way GPS fixes are currently obtained. GPS devices can obtain fixes at least three different ways. The least sophisticated method downloads a set of current satellite orbits by downloading frames. If part of a frame is corrupted, the GPS device must wait 30 seconds for it to be retransmitted.

A slightly more sophisticated approach uses an initial estimate of the current time and your position to obtain a lock more quickly. Finally, instead of downloading orbit and position data from the satellites, some modern GPS devices simply recalculate the information locally. Some (or all?) of these optimizations are supported by the Freerunner's GPS device, though the software installed at the factory does not seem to make use of them.

More Info to get a fix

I'd like to stress what is written above, it really helped. I put my FR on a table outside, standing vertically with something to hold it upright, switched to the SS display, clicked the db button, waited about 2 mins to get a bar, then turned it around its vertical axis slowly watching the bar go up and down. When it was facing the right way for a maximum bar length I left it like this, without touching it for about 10 mins, and it was able to find the other satellites and get a fix. It is important to not touch it or move it once it gets the first satellite. However it did lock up solid after about 30 minutes, and power button did not reset, needed to remove the battery which of course lost the fix.

Information about faulty antennas

  • If you list your problems above, note if you've tried unplugging and replugging the internal GPS connector. (See Disassembling_Neo1973 about 2/3 of the way down. (this may differ on freerunner, pictures appreciated)

FreeRunner_GPS_antenna_repair_SOP Indicates that the problem may be bad soldering, and includes a guide to fix. This will presumably void your warranty.