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CC1354P10: Unable to receive messages when Tx packet marginally changes from centre frequency

Ed CURRIE
Prodigy 40 points
Part Number: CC1354P10
Other Parts Discussed in Thread: CC1101

Hi,

Working with CC1354P10  at 868,30MHz, data rate 38.4kbps, 50Khz deviation , FSK  and having receive issues whereby receiver cannot track marginal offsets in  Transmitter centre frequency.

eg.

When Tx message ( packet constructed using signal generator) is sent exactly at centre frequency of 868.30MHz the CC1354P10 receives ok but if i change Tx frequency at signal generator by +/-25khz it no longer receives the message.

I have set rxBw at 270khz.

However if i initially power up the Rx at +/-25khz from centre or even +/-50khz from centre ( i.e 868.25, 868.35MHz) it works ok now but will not work if i change signal generator back to  centre freq  (868.30MHz) unless i do a power on reset again

It seems like after power up the frequency tracking range is very narrow band ......any ideas what issue could be or register settings to check ??

Thanks,

Ed Currie

  • 0
    TI__Mastermind 33170 points

    Hi Ed,

    If you change the frequency offset on the signal generator whilst you are transmitting, then the internal oscillator will need to re-calibrate the change in the frequency offset by leaving the Tx mode. The initial frequency offset is based on the signal generator offset when the Tx transmission starts. If you do a power on reset or leave Tx - standby then re-join Tx, the new frequency offset will automatically be compensated for.

    I'll double check what the frequency offset is for the 38 kbps PHY you are using. We measure this in the PER v LEVEL v freq. offset tests. It is advantageous to keep the Rx bandwidth as tight as possible in order to gain extra sensitivity performance. 

    Regards,

       Richard

  • 0 in reply to RGW
    Prodigy 40 points

    Hi Richard,

     

    Thanks for the quick reply and couple of follow up questions

     

    1. Is the frequency offset for the 38kbps PHY a fixed or configurable value ( eg could I widen this so that in my Rx sensitivity tests it automatically tracks Signal generator changes when I dynamically offset this by +/-50khz at signal generator end ?....  When I simultaneously run the Rx sensitivity test using CC1354P10 and one of our legacy products based on CC1101 it is only CC1354P10 Rx test that doesn't track the frequency adjustments at Signal Generator ( That said I'm not sure how the code for legacy product was developed)?

     

    1. & Touching on your Rx bandwidth setting comment ... can you suggest an optimum Rx bandwidth setting for my setup , 38.4kps, 50khz deviation, 10ppm xtals in the Rx & Tx 1354 devices.

     

    Thanks,

    Ed.

  • 0 in reply to Ed CURRIE
    TI__Mastermind 18065 points

    Hi Ed,

    To comment on your second question, the following App Note is relevant for our CC13xx devices for explaining the process of selecting the optimum RX bandwidth setting:

    SWRA122 (CC11xx Sensitivity Versus Frequency Offset and Crystal Accuracy): https://www.ti.com/lit/swra122

    You can also refer to Section 4 of SWRA682 (Finding Settings for new PHYs for the CC13xx Family): https://www.ti.com/lit/swra682

    Regards,

    Zack

  • 0 in reply to ZC
    Prodigy 40 points

    Hi Zach,

    Thanks for sharing this App Note info.

    Regards,

    Ed.