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LAUNCHXL-CC1310: Custom PCB Based on Reference Design can't do packet RX/TX but continuous mode works

Part Number: LAUNCHXL-CC1310

I worked on a custom PCB that is supposed to be able to receive transmissions, however on SmartRF during testing I can't get it to transmit or receive packets. I have two Launchpad XL's where they can talk to each other and transmit/receive packets fine, but when I remove either launchpad and replace it with my PCB, it can't receive/transmit packets. To be clear, it will transmit packets and says DONE_OK in the output window, however the Launchpad won't receive anything. Vice versa doesn't work either where the Launchpad transmits and the custom PCB receives. 

Interestingly, though, continuous mode works with both the Launchpad and the custom PCB being either the receiver or transmitter, although signal power isn't stellar as the max I see is -20dB gain on either devices being the receiver. The gain is also very inconsistent:

This is with the custom PCB being the receiver, and the Launchpad shows something similar when it's the receiver. Any idea why this could be happening? I initially had the wrong type of 24MHz crystal oscillator connect where it had a ground, VCC, tri-state, and output whereas our design was meant to use a crystal with two grounds and two pins being the connections to the oscillator and I ran it like that before realizing I needed to change the crystal I used. Could that have damaged anything? When that incorrect crystal was in, the custom PCB wouldn't even try to start transmitting or receiving as it would be stuck in an IDLE state.

I will link the github that has our PCB schematic and gerber files if you wanted to look at that: Emrick/hardware/Emrick at main · eduxstad/Emrick · GitHub

Any help would be appreciated here. I'm baffled as to why I can't do packet transmissions but I can do continuous. We also used the antenna design from the Launchpad, and we removed C12 so there isn't a connection currently to the external antenna, just a connection to the onboard antenna, AE1.

  • Most likely frequency offset. Try to adjust the frequency up/ down on either receiver or transmitter and see if that improves things.

  • Hi Zareef,

    Looking at your PCB design I found a couple of issues that affect RF performance related to your ground:

    1. There is no solid ground plane. We recommend having layer 2 on your pcb as a solid ground plane with no other signal or power traces on that plane. For the type of antenna used (monopole), the ground plane is part of the antenna and not having a proper ground plane will affect performance.

    2. The ground plane has to extend up to where the antenna starts. As a reference, below is an image of the top layer and second layer of the LAUNCHXL-CC1310 design and images from your design.

                        Top layer                                                                                         Bottom Layer

                         

    3. There should be a ground plane under the RF path. Please look at the images above. On the reference design there is a solid ground under the RF components and the feed line to the antenna.

    4. It seems like there is a trace crossing under the RF components. Avoid having any traces cross under the RF path.

    I highly recommend reviewing the LAUNCHXL-CC1310 design files and following the reference design as closely as possible. You can find the files here: LAUNCHXL-CC1310 Evaluation board | TI.com

    It would also be a good idea to take a look at CC13xx/CC26xx Hardware Configuration and PCB Design Considerations (Rev. G)