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I am designing my first transceiver (first PCB/IC that uses an antenna). I chose SX1261/2 because it is cheap and supports LoRa protocol. While designing the PCB and reading the datasheet of the IC I have some questions. I did make a previous question about the subject. I am making the current question with some more practical questions.

Looking at the reference design:

sx1261 reference design

Considering VR_PA and RFO pins:
-What I understand is that VR_PA connects to RFO to provide it with a variable bias voltage. The C1, C2, L1 components are selected to reduce output ripple of the VR_PA.
What should I do:
I can select the C1, C2 and L1 components other than the optimal recommended the BOM provides, based on my measurements of the oscilloscope at VR_PA pin to reduce its ripple (even more lets say). For example I can use another C capacitor in parallel with the C1, C2 to reduce the ripple even more, or use a larger inductor L1 for the same result.

Considering RFI_N and RFI_P pins:
-What I understand is that RFI_N and RFI_P are differential input pins. Differential inputs are used to reduce noise/improve accuracy. These two inputs should have a 180o shift of the input voltage between them.
What should I do:
I should calculate the matching network to RFI_N (the negative input) first and then calculate the values of the components to bias the RFI_P (the positive input) with the 180o difference from RFI_N. Or should I do the FRI_P first? I am confused on that one.

Considering the balun:
-The datasheet recommends using PE4259. I would like to keep the antenna as simple as possible, as this will be my first design and I would like to analyze just the antennas without using a balun (To make the analysis and design easier). So I would like to design the PCB with both the antennas separate like that (the antenna's shape shown here will not the actual end-design shape):

sx126x antennas without balun

I did read somewhere that designing both antennas like I want to do might end up burning the input antenna while I use the output antenna to transmit data. If this is the case, I will use one PCB only to transmit data and physically remove the copper of the receiver antenna, and I will use another PCB only to receive data, physically removing the copper of the transmit antenna. So I will end up with only 1 antenna per PCB.

Questions:

  1. Are my "What I should do" ideas about the 4 pins I mention correct? Especially the one I ask whether I should match the antenna to the RFI_N or the RFI_P first, and then give the other pin the 180o shift.
  2. Can I design my first PCB antennas without a balun to simplify my design? (And simply remove/strip away the copper of either of the antennas that I wont use?) - assuming I will have enough space to design both my antennas of course-.
  3. Should I order the PCB with both antennas and just remove the antenna that I wont use in each design? (receiver/transmitter)? Or it is ok to leave both antennas on the PCB and just use the receiver/transmitter?
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    \$\begingroup\$ 1. Regarding RFI_N and _P - doesn't matter. Make sure that there is no DC path to ground - No shunt inductors without a DC blocking cap. 2. Your PCB doesn't follow the reference design, you are on your own. 3. I would copy the reference design and use a 50 ohm antenna with a connector 1st. It is easier to connect to a VNA this way. \$\endgroup\$
    – Lior Bilia
    Jun 8, 2023 at 18:41

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