Qualcomm WGR7640 Only Seeing SBAS Satellites?


#1

Hello everyone,

We are trying to get the Qualcomm WGR7640 (WGR7640017WLNSPTR320 to be exact) working but we’ve hit a snag. Our initial tests show the system only catching SBAS satellites, but nothing else. What is strange is that it can see 6-8 SBAS pretty quickly, but no GPS satellites ever. We also can’t get a fix. Do any of you have some insight into this issue? We don’t believe this is a hardware issue because the SBAS signals show up quickly and strong (all 30+ SNR), but there are absolutely no GPS signals that appear. It’s almost as if the software/driver is filtering out the GPS signals.

Any help is much appreciated.

Thanks,
Trent


#2

Hi @toshiro

I am looking for a couple bits of information to help debug the issue: Are you running these tests on the 410c DragonBoard? Do you have any other electronics (such as a display) close to the GPS circuitry?

Full disclosure: I am an employee of Qualcomm Canada, any opinions I may have expressed in this or any other post may not reflect the opinions of my employer.


#3

Hey @ljking,

We’re running it on our own custom board but it uses the APQ8016 in a very similar setup as the Dragonboard. We do have a display above the board, which was on when we caught the SBAS satellites, hence our hypothesis that it isn’t a hardware issue.

Thanks,


#4

Hi @toshiro

The GPS circuitry is VERY sensitive to noise and must be well shielded. This is the reason we added a shield over the CPU, memory and power supply on the 410c DragonBoard, noise was escaping from the CPU and interfering with the GPS. The SBAS signals are much stronger than the GPS signals, and at a slightly different frequency. If you have a noise source (lets say the display as an example), it could have a spur in the GPS band and hence jamming the GPS, but not affecting the SBAS signals.

Did you follow the layout guidelines for the GPS section of your board? See chapter 6 here: https://developer.qualcomm.com/download/sd410/apq8016e-processor-design-guidelines.pdf The I/Q lines from the WGR to the APQ are particularly sensitive and must be well guarded from electrical noise.

Did you select a high quality crystal for the board? If you used a low quality crystal, or a MEMs oscillator the GPS will not work. See the app note on Crystals here: https://developer.qualcomm.com/download/sd410/gps-quality-192-mhz-2520-package-size-crystal-and-thxtal.zip

As a first start I would suggest you test your software and antenna on the 410c DragonBoard. Instructions for connecting an external antenna to the 410c DragonBoard are here: https://developer.qualcomm.com/download/db410c/adding-ufl-antenna-connectors-and-validating-gps-android-application-note.pdf

Full disclosure: I am an employee of Qualcomm Canada, any opinions I may have expressed in this or any other post may not reflect the opinions of my employer.