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Ground Plane trouble with FGPMMOPA6H
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Ground Plane trouble with FGPMMOPA6H

by Adam_Xstream on Wed Oct 25, 2017 9:45 pm

Hello Adafruit Community.

I'm struggling to get performance from our FGPMMOPA6H GPS module which we have mounted to our custom PCB. We really liked the performance of this chip when we used it as a breakout board, however, when we mount it to our PCB the module is unable to find a fix.

I was hoping to check in with the community and see if others had successfully mounted this module to their designs and if they had any problems like the ones we are having.

I am also interested in people's thoughts on our use of ground plane below the chip. We did this to isolate it from noise, but its so different from the original breakout board, I am concerned we inadvertently messed up one of the features.

FGPMMOPA6H Datasheet

Thank you for your help!

Adafruit mounting. These board work wonderfully! However, they have traces going directly under the module!

Adafruit Ultimate Breakout Board.png
Adafruit Ultimate Breakout Board.png (141.6 KiB) Viewed 1287 times

Our way of mounting to the PCB. Notice the large ground plane (Purple). We thought this would improve performance, but maybe we've made it worse by doing this?
Adam Mouting GPS.png
Adam Mouting GPS.png (48.11 KiB) Viewed 1287 times

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Re: Ground Plane trouble with FGPMMOPA6H

by adafruit_support_mike on Thu Oct 26, 2017 12:18 am

You have to be careful about the spacing of a gound plane near an antenna.

The fixed 0v surface acts like a mirror for radio waves, and the reflections will make a single-wire dipole antenna see what amounts to a copy of itself an equal distance behind the plane. With the right combination of distance from the ground plane and electrical path distance through the antenna, you can get the effect of an antenna twice as wide. Other combinations can cause interference that cancels the signal though, making the signal reception worse.

Try etching away the ground plane below the GPS module on one of your boards and see if that makes things any better.

Beyond that, you really need a simulator with a good RF package to get the details right. Small changes can make a big difference in performance.

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Please be positive and constructive with your questions and comments.