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CC1352P: FCC certification test, power spectral density failed in 125Kbps

EvanWuCN
Intellectual 325 points
Part Number: CC1352P

Hi,

We are processing the FCC certification test for our CC1352P module, which is 20dB output power on the 2.4GHz band, and we observed a fail on the Power Spectral Density test with 125Kbps, while other datarates passed.

Here are the data plots for your reference.

Low channel PSD:

Mid channel PSD:

High channel PSD:

We observed the same result on the TI launchpad: LAUCHXL-CC1352P-2. From the plots, we can see two spikes that are not seen with other datarates.

Are there any solutions? Looking forward to your reply.

Thanks and Best Regards,

Evan

  • 0
    TI__Guru**** 317180 points

    I have to check internally what we have looked into here. I will get back to you when I get more information.

  • 0 in reply to TER
    TI__Guru**** 317180 points

    How have you measured the PSD in detail? 

  • 0 in reply to TER
    Intellectual 325 points

    1. I used below setting on Smart RF Studio 7.

    2. I connected the module to the Spectrum Analyzer through an SMA connector and got blow plot.

    3. Please note that the resolution bandwidth is 3 kHz, so from the plot, we can see the peak PSD is 8.018 dBm/3KHz, which is exceeding the limit (8 dBm/3KHz).

  • 0 in reply to EvanWuCN
    TI__Guru**** 317180 points

    I haven't been able to find the exact details on how this should be measured other than it should be measured according to FCC KDB 558074 that outlines the measurement procedure. 

    But I found this: https://apps.fcc.gov/eas/comments/GetPublishedDocument.html?id=237&tn=158724

    This indicate  that the PSD could be measured with a different RBW than 3 kHz. 

  • 0 in reply to TER
    Intellectual 325 points

    Thank you for sharing the measurement procedure. It seems there are different ways of conducting the measurement.

    I am not an expert on certification tests, but the way I am using for the measurement is what the certification lab is using too. And they told me, with the PA enabled, the result failed.

    So what I am concerned about is that with 125Kbps data rate, would it be able to pass FCC certification with PA enabled or it wouldn't so we can not use 125Kbps data rate when PA is enabled.

  • 0 in reply to EvanWuCN
    TI__Guru**** 317180 points

    Which measurement procedure is the lab following? How to do all measurements are described in various FCC documents and it would be useful to find out which one they are using. 

  • 0 in reply to TER
    Intellectual 325 points

    Here's the procedure they are following.

    The measured power spectral density was calculated by the reading of the spectrum analyzer and
    calibration. Following is the test procedure for PSD test:
    a) Set analyzer center frequency to channel center frequency.
    b) Set the span to 1.5 times DTS
    c) Set the RBW to 3 kHz
    d) Set the VBW to 10 kHz
    e) Detector = peak.
    f) Sweep time = auto couple.
    g) Trace mode = max hold.
    h) Allow trace to fully stabilize.
    i) Use the peak marker function to determine the maximum amplitude level within the RBW.

  • 0 in reply to EvanWuCN
    TI__Guru**** 317180 points

    I have to double check with the team in Dallas. Due to the power outage there at the moment I won't be able to follow this up before next week. 

  • 0 in reply to TER
    TI__Guru**** 317180 points

    This looks correct according to the information I have received. I believe one option is to argue with the lab about the intent of the standard (refer to the link I posted in an earlier post) or use some backoff to pass the PSD requirements.