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I'm trying to use an active antenna with the GY-GPSV3-NEO-M8N GPS module. In the hardware manual for NEO-M8N it is said that I need a DC bias circuit like shown in the picture below. enter image description here

As shown I need RLC components connected to RF_IN and VCC_RF. I'm not embedding the GPS chip to my PCB so I need to change the components on the blue module itself. But I'm not certain which of the components is connected to which pin.

enter image description here

The antenna I'm trying to use has the specs shown in the picture below: enter image description here

I was told I need to be aware of the bias circuit to use any active antenna as well as the max gain of the GPS module.

Question #1: There are 2 components near the RF_IN pin in the blue module. (The ones inside the yellow box on the picture above.) The white component is for sure connected to RF_IN (I'm also not sure whether this is an inductor or not) and the resistor on the left. But I'm not sure where the resistor is connected. The bias circuit schematic from the datasheet says that the resistor next to the inductor needs to be connected to VCC_RF but this resistor seems to be connected to the pin next to VCC_RF, so RESET_N enter image description here

Question #2: Should I seek a GPS antenna with lower gain? Max gain for this chip is said to be 30dB in the datasheet. The antenna that I picked has 28+-2dB gain. Is it better to go for 22dB? ,

Any help is very much appreciated thank you for reading.

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2 Answers 2

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Judging by the text printed on the PCB, Addicore uses the same board for 6M, 7M & M8N modules.

The NEO-6M requires that pins 8 & 9 are connected together, so when a NEO-M8N is populated it has its RESET_N and VCC_RF pins connected together.
Although this probably does no harm to the M8N module, I wouldn't be surprised if it causes trouble if the VCC_RF output is controllable by the module and can be switched off by a command over the UART interface - I'd expect that the current draw by the active antenna might pull the combined RESET_N/VCC_RF low enough to reset the module.

Aside from that it seems that the necessary components are populated on the PCB for use with an active antenna.

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  • \$\begingroup\$ I haven't done much investigation on the modules reset part but I'm assuming that pin needs high voltage for the module to work. So can I rip the connection between VCC_RF and reset and solder a jumper between RESET and main VCC and then connect my active antenna? \$\endgroup\$
    – Exclose
    May 15, 2021 at 14:28
  • \$\begingroup\$ If you can get at the link between those 2 pins then yes, that's what I'd do - cut that link. You should not need to worry about connecting pin-8 (RESET_N) to Vcc because the module has an internal 11k pullup. \$\endgroup\$
    – brhans
    May 16, 2021 at 0:11
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  1. Looks like the required components are already there. Just about all GNSS antennas are active, so the DC injection tends to be standard on most boards. The module doesn't implement it internally as you may want to switch it on and off to conserve power.

  2. More gain is usually better. With GNSS, you're trying to pick a signal out of noise.

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  • \$\begingroup\$ Also note the datasheet explicitly states an active antenna \$\endgroup\$
    – Kartman
    May 15, 2021 at 13:05

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