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CC1310: 3.3K sidebands seen when CW is turned on at 868.5MHz....Help needed

Part Number: CC1310

I have written a code to switch between continuous CW and modulated wave. Unfortunately during the CW mode (standalone CW and combination code), I am getting sidebands at 3.3 kHz as seen from the RF spectrum analyzer. I am using the same settings as from the code composer studio with the rfCMdTxTest struct.

Should I use radiosetupstruct ? but when I use that I'm not even getting the output

Sometimes when I use run cmd it's ok, but most of the time post cmd leads to these sidebands.

I wish I will get a helpful answer on this.

RF_postCmd(rfHandle, (RF_Op*) &RF_cmdTxTest, RF_PriorityNormal, NULL, 0);

rfc_CMD_TX_TEST_t RF_cmdTxTest =
{
.commandNo = 0x0808,
.status = 0x0000,
.pNextOp = 0, 
.startTime = 0x00000000,
.startTrigger.triggerType = 0x0,
.startTrigger.bEnaCmd = 0x0,
.startTrigger.triggerNo = 0x0,
.startTrigger.pastTrig = 0x0,
.condition.rule = 0x1,
.condition.nSkip = 0x0,
.config.bUseCw = 0x1,
.config.bFsOff = 0x1,
.config.whitenMode = 0x2,
.__dummy0 = 0x00,
.txWord = 0xABCD,
.__dummy1 = 0x00,
.endTrigger.triggerType = 0x1,
.endTrigger.bEnaCmd = 0x0,
.endTrigger.triggerNo = 0x0,
.endTrigger.pastTrig = 0x0,
.syncWord = 0x930B51DE,
.endTime = 0x00000000,
};

Thanks

Subil Krishnan

  • To be able to help you you need to show the code and how you are switching between modes. The command is the same regardless of you using post or run. If you want to change from modulated to un-modulated, you need to exit the modulated TX by cancelling the TX command, reconfigure the CMD_TX_TEST command and then re-send it.

  • Hi Siri, thanks for your reply, the sidebands are there on the code, regardless of my switching. So even if I just power up the unit in CW mode with the above-posted cmdtxtest struct, it produces sidebands. 

    Is there any issue with the struct?

    and will ADC, etc peripherals cause issues to this?

    To my surprise, it doesn't produce sidebands while debugging.

  • Not an RF Expert so I need to re-assign this case to someone in the RF team, but please verify that you see this behavior when you are running the default rfCarrierWave example from the CC1310 4.10 SDK.

    BR

    Siri

  • Could you post a screen shoot of how your spectrum looks like? I want to see how the sidebands looks like?

  • This is how it looks like

  • This looks more like a modulated signal. 

    - If you run the rfCarrierWave example, do you then get a clean CW? If yes, what is the difference between the example and your software setup? 

  • I have tried the example and directly from Smart RF studio, both give a clean wave. The main change in this is I use postcmd(). I couldn't think of anything else

  • postcmd() only set non blocking run. 

    Could you set a breakpoint on 

    RF_runCmd(rfHandle, (RF_Op*)&RF_cmdTxTest, RF_PriorityNormal, NULL, 0);

    or you equivalent and check the setting for the RF_cmdTxTest command before you send the command in case the correct setting has not been set or has been overwritten. 

  • HI

    While we were trying things, we think we found the source of the noise.

    The sidebands are seen when an Output pin on my board is toggled at high frequencies. (Yet to do the test on a floating Output pin which is not connected to any line)

    We have an onboard watchdog chip that needs to be cleared before the timeout by sending a pulse from the MCU. As to prevent the board from resetting we were doing this continuously (gets called most of time in a while loop with a very negligible delay).

    We confirmed its effect by toggling the pin with a delay so that the effective rate of pulse happening will be reduced and this has reduced the sidebands frequency/ amplitude.