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I am currently working on a GPS module tracking a drone-mounted device. I am using the ublox CAM-M8Q GPS module on a breakout board.

The internal antenna is working fine, however the signal is rather bad so I'm trying to use the external antenna. I'm using the hardware integration manual from ublox for reference for connecting the antenna. This it the external antenna with LFA I am using. As pointed out in this thread I connected the supply voltage for the LFA as such:

Sorry for a paint schematic, I'm not able to use EAGLE right now

However with the antenna connected like this I'm not getting any signal. What did I do wrong and how can I improve this circuit?

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  • \$\begingroup\$ Use 100 kΩ(typ.) external pull down resistor at LNA_ENsignal whenever the signal is used externally have you done this? \$\endgroup\$
    – User323693
    Feb 25, 2020 at 13:33

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If you are you using the U-Blox development board, you'll need to rotate this resistor (bright green highlight):

enter image description here

This way:

enter image description here

And connect the active antenna to the "RF_In" U.FL connector.

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  • \$\begingroup\$ Okay, but do I need to keep my circuit with the inductor and the capacitor? \$\endgroup\$ Feb 25, 2020 at 13:35
  • \$\begingroup\$ Yes, of course. You don't want to be feeding DC into the uBlox RF input. \$\endgroup\$
    – Dave Tweed
    Feb 25, 2020 at 14:20
  • \$\begingroup\$ @OccasionalPoster Sorry, to clarify keep your circuit as-is, only do this change :) \$\endgroup\$
    – eeintech
    Feb 25, 2020 at 14:33
  • \$\begingroup\$ @Cisco25 I did change it, still no signal \$\endgroup\$ Feb 25, 2020 at 15:10
  • \$\begingroup\$ @OccasionalPoster Strange, did you wait long enough? Sometimes it takes 5-10 minutes for the receiver to acquire satellite signals. Are you using U-blox center to check what the receiver is seeing? In this guide, they recommend to add a 10-Ohm resistor in series with the inductor, measuring the voltage across that resistor could tell you if the antenna LNA is drawing current or not: u-blox.com/sites/default/files/products/documents/… \$\endgroup\$
    – eeintech
    Feb 25, 2020 at 15:53

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