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CC1310: FSK modulation, 500kbps with 250kHz deviation is not showing good spectrum

user4956992
Prodigy 30 points
Part Number: CC1310


Hello.

I am experimenting 500kbps 2FSK modulation using 250kHz deviation on 920.0MHz, (from SmartRF)

But by looking at the spectrum, it is showing a different from what I am expecting.

The picture shown below is 2FSK, 500kbps, 250kHz deviation but the bandwidth is too narrow.

By checking the modulation, 0x1F40 is used. (modType 0, deviation 3E8)

This spectrum shape is the same as 125kHz deviation by some reason.

I believe that CC1310 works on FSK 500kbps

  • Is my understanding correct?

Note that I can set 200kHz for deviation and it make sense. Please see the spectrum below.

Thank you.

  • 0
    TI__Mastermind 36395 points

    user4956992,

    I have downloaded the latest version of SmartRF Studio 2.8.0 and performed a couple of modulation tests like you have done and here are my results.

    Sorry about the image, but its taken with a phone.

    • White trace is 500kbps, 250kHz deviation, 2FSK using RBW/VBW of 30kHz.
    • Blue trace is 500kbps, 125kHz deviation, 2FSK using RBW/VBW of 30kHz.

      I see modulation width very close to what I would expect and not exactly what you are seeing.

    Here is my matlab simulation for both

    • This one compares with the white trace is 500kbps, 250kHz deviation, 2FSK using RBW/VBW of 30kHz.

    • This one compares with the blue trace is 500kbps, 125kHz deviation, 2FSK using RBW/VBW of 30kHz

    I think you might be using an earlier version of SmartRF Studio and it might have a bug, can you please upgrade to the new version that was released on December 20th, 2017. (version 2.8.0)

    Regards,
    /TA

  • 0 in reply to TA12012
    Prodigy 30 points

    Dear TA12012.

    Thank you for your prompt reply.

    I understand that the modulation works and I have tested and confirmed.

    Reason for unexpected spectrum was my fault and CC1310 works as we expected for deviation 250khz for br500kbps.

    For my testing, I modified register setup based on 625bps long rainge mode, but some of setting for FEC and others were remained as it was.

    So, what I have done was that:

    Updated to the latest Smart RF (v2.8.0) as you suggested.

    2FSK modulation parameter created based on 50kbps 2GFSK from Typical Setting. (simply by changing modulation from command view, then change bitrate, deviation, RX filter BW from RF parameters view.)

    Then I've got the same result as you shown here.

    Thank you very much for your help.

    Best regards.