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CC2640 Broadcasting at 2401 MHz

Chris Necklas
Prodigy 70 points
Other Parts Discussed in Thread: CC2640

We have two sample beacons using the CC2640 chip that are broadcasting at 2401 MHz when they should only be broadcasting from 2402 to 2480. Looking for reasons why this might be. Thanks for your help.

  • 0
    TI__Guru** 105180 points
    Hello Chris,

    Do you have a spectrum analyzer plot you can attach? Note that the center frequency is 2402MHz, but you will still observe power around the center freq. The allowable emissions is describe in the BT core spec.

    The LE system operates in the 2.4 GHz ISM band at 2400-2483.5 MHz. The LE system uses 40 RF channels. These RF channels have center frequencies 2402 + k * 2 MHz, where k = 0, ..., 39.

    Please refer to "3.2 SPURIOUS EMISSIONS" in the BT4.0 core specification, Vol 6, Part A.

    Best wishes
  • 0
    TI__Mastermind 29650 points
    Chris,

    Broadcasting / Advertisments in BLE is on channels 37/38/39 (2402, 2440, 2480MHz).
    It is broadcasting at 2401MHz when you want 2402MHz or for all channels?

    If it is when trying to broadcast at 2402MHz then it is most likely due to a ~ -40ppm offset on the crystal frequency. Can you share a schematic of your board and details on which 24MHz crystal that is used?
    The CC2640 has by default connected 9pF load capacitance internally. If you also have external load capacitance then this might be the reason for what you are seeing.

    Regards,
    Svend