NRF9160 GPS circuit for large patch antenna w/o amplifier

[GJSea]

Hi,

I was wondering what is the recommended GPS circuit would be for an always outdoor device with a large patch antenna, without the need for an amplifier. Would the following suffice? (GPSIN comes directly from the NRF9160 LGA)

Also currently gps_channel_get is returning the 6325.242,N,01026.136,E which is in Norway and I'm in Seattle - Is this coordinate the default 'unknown location' coordinate rather than 0,0? I'm on the latest 0.4.0 tag and latest modem firmware.

Thx!

[Amanda Hsieh]

Hi, 

I was wondering what is the recommended GPS circuit would be for an always outdoor device with a large patch antenna, without the need for an amplifier.

The external LNA is reccomended to get a good enough noise figure for GPS RX. 

Would the following suffice? (GPSIN comes directly from the NRF9160 LGA)

 It depends if you have LTE antenna on the same board. Do you plan to have an LTE antenna on the same board?

Also currently gps_channel_get is returning the 6325.242,N,01026.136,E which is in Norway and I'm in Seattle - Is this coordinate the default 'unknown location' coordinate rather than 0,0? I'm on the latest 0.4.0 tag and latest modem firmware.

The asset_tracker only uses simulated GPS, where the default postition is in norway. Using the built-in GPS in the asset tracker sample is not implemented yet. This will be implemented in the future. For now, we have a stand-alone GPS sample that can be used to test the GPS in NordicPlayground. 

 

 Best regards,

Amanda

[GJSea]

Hi Amanda,

We decided to use a readily available GPS LNA, the Infineon BGA715N7, which has a nice +20dB gain as the QM14501 doesn't seem to be available anywhere. Below is my schematic, does anything stand out as overlooked swapping out the QM14501 for the BGA715N7? My input traces are balanced to 50 ohm as best as possible.

I got the stand alone GPS sample working so know how to implement this now, however on the NRF9160 DK 0.8.2 board using the on-board antenna it never locks onto a satellite, Tracking is always 0, let alone get a coordinate, this was in various countryside outdoor locations testing for over an hour. Any idea why the DK and the GPS sample aren't picking up a satellite?

Thanks!

[Amanda Hsieh]

So one potential issue though: when the LTE radio is operating, the RF signal can demodulate in the GPS LNA input stage and create unwanted harmonics. To avoid this, either use a band pass filter before the LNA, use a RF switch to disconnect the GPS antenna when the GPS_EN signal is off or an LNA that has the filter on the input.

The nRF9160 DK comes with an on-board antenna for GPS, but on some boards this antenna is not functional on board versions up to and including v0.8.2 due to this errata. Please see this post to use external GPS antenna on nRF9160 DK.

-Amanda