Antenna bias voltage below ANN-MB spec (2.65V < 3.0V) about qwiic_gps-rtk2 HOT 3 CLOSED

How are you measuring the voltage in the field? I'm seeing 3.3V at the SMA port on the four units I have on hand.

We worked with u-blox directly for this design and they gave us a scary amount of feedback on our first submission. They may have missed this but I suspect the design is correct and the documentation is behind.

from qwiic_gps-rtk2.

How are you measuring the voltage in the field?

Unfortunately, I don't have a Sparkfun board to test this with, but I have a simplertk2b, which appears to use the same antenna bias supply as the Sparkfun board and the F9P integration manual's reference design (Fig. 40). Primary difference is that the simplertk2b uses a (too?) small 10 Ω short circuit current limiting resistor (R11). With that it can deliver 3.08 V to the SMA port with an ANN-MB connected. I measured this voltage between the bias inductor's pad on the RF trace and the SMA connector's ground. See the below image for details and a few more voltages.

Using a 33 Ω current limiting resistor (the Qwiic_GPS-RTK2's R14), the bias voltage at the SMA connector should be approximately 2.74 V.

I'm seeing 3.3V at the SMA port on the four units I have on hand.

Is that with an antenna (preferably u-blox ANN-MB) connected or just the open circuit voltage? In my case, the latter is exactly the F9P's VCC measured at the VCC decoupling cap.

We worked with u-blox directly for this design and they gave us a scary amount of feedback on our first submission. They may have missed this but I suspect the design is correct and the documentation is behind.

I'm currently designing a breakout board for the ZED-F9T, because the RCB-F9T does not meet my requirements. I was looking at your design for some inspiration in addition to the F9T integration manual. Thank you for letting me know that u-blox gave you feedback on your design. I guess I will contact them regarding my concerns.

from qwiic_gps-rtk2.

@nseidle: I've added a schematic to my initial post, hoping to make my point a little clearer.

I want to use a 50 mA survey antenna, so for my F9T design I'll likely rely on a separate LDO with internal foldback current limiting for the antenna bias supply to obviate the need for a current limiting resistor or the BJT circuits suggested by the integration manual (Fig. 39):

from qwiic_gps-rtk2.