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LAUNCHXL-CC1310: How to set TX power in CC1310

Mike Persson
Prodigy 80 points
Part Number: LAUNCHXL-CC1310
Other Parts Discussed in Thread: CC1310

Hi!

I have tried to set TX power using the EasyLink_setRfPwr(int8_t i8txPowerdBm), in CC1310 LAUNCHXL, and it returns EasyLink_Status_Success for an input <= 12 dBm, which is expected! But the RSSI does not change when I change the power. Also, when I use EasyLink_getRfPwr(), it returns the value I just set.

I send messages between two CC1310 just 10 cm apart so the default RSSI at this distance is -15 dBm. The weird thing is that when I set power to 12 dBm, I get the same RSSI.

So, is this how it should be acting or is there something I have missed?

  • 0
    TI__Guru**** 317180 points
    The RSSI on CC1310 saturate on about -15 dBm in. This means that if you have higher input power than -15 dBm CC1310 will still show the RSSI as -15 dBm. To see the effects I would at least place the RX and TX side 2 m apart.
  • 0 in reply to TER
    Prodigy 80 points
    Okay thanks! However, there is like no difference between txPower = 1 dBm and txPower = 12 dBm, when between 2 and 10 meters apart either (not free space). Maybe even larger distances are required to notice difference?
  • 0 in reply to Mike Persson
    TI__Guru**** 317180 points
    Ok, which RSSI do you see when you are 2 m apart?
  • 0 in reply to TER
    Prodigy 80 points

    Depending on the angle of the launchpad I get, 30 dBm at best and 60 dBm in the worst case.

    Here's a description of the test:  Node 1 (txPower = 1 dBm) sends a packet. Node 2 (txPower = 12 dBm) receives the packet and saves the RSSI in a new packet, which it sends back to Node 1. Node 1 displays both RSSI values.

    A strange thing is that, when the RSSI differs between the two transmissions, RSSI(Node1 -> Node2) is often stronger than RSSI(Node2 -> Node1), even though Node2 has the highest TX power. Does the higher TX power setting affect the receive operation as well?

  • 0 in reply to Mike Persson
    TI__Guru**** 317180 points
    Do you get the same if you use the EasyLinkRx and EasyLinkTx right out of the box (the only modification is the TX power setting?
  • 0 in reply to TER
    Prodigy 80 points
    Yea at a distance of 2 m I get the ~same average RSSI, -36 dBm. So, would you say it's working properly?
  • 0 in reply to Mike Persson
    TI__Guru**** 317180 points
    Not sure what you mean. Do you measure -36 dBm independent of the txPower setting?
  • 0 in reply to TER
    Prodigy 80 points
    Sorry for being unclear. I got -36 dBm with txPower = 12 dBm, both in the RX/TX example projects and in my own project. I then tested txPower = 1 dBm for Node 1 and kept txPower = 12 dBm for Node 2 in my project, like I have tried before. This time, when Node2 -> Node1 got -36 dBm, Node1 -> Node2 got -44 dBm, which seems like the proper behaviour.

    Probably I did something wrong in the previous tests, or the propagation was very different for the two nodes. However, it looks like it's working fine now. Thank you :)