CC2652RB: Power level for Modem Test command differs from application behavior

Chris Hunt

Part Number: CC2652RB

We have sent devices (based on SimplePeripheral) away for regulatory certification testing, and they are reporting that our conducted samples output 25 dBm less when using HCI_EXT_ModemTestTxCmd as compared to the power output of standard BLE advertising. We use the DEFAULT_TX_POWER of 0 dBm, and don't ever change it, for advertising or for the test mode. Any reason why there would be such a large discrepancy?

over 5 years ago

0 Marie H over 5 years ago

TI__Guru* 83011 points

Hi Chris,

What version of the SimpleLink CC13x2/CC26x2 SDK are you using?

I agree this sounds very strange. As you say, 0 dBm is the default value both for advertisements and for the HCI_EXT_ModemTestTxCmd.

In general you can check out our app note on certification here:

0 Chris Hunt over 5 years ago in reply to Marie H

Intellectual 945 points

We are using version 3.20 of the SDK. I am aware that is not the current version, but it is the version that is on the boards in the test labs 3000 miles away. We were told by TI that we could progress with testing using that version of the SDK without issue. So if this SDK-specific as it seems you are suggesting, then I am asking specifically about our current setup in 3.20. We are not interested in getting the test samples back, updating them, and sending them back to the lab unless that is a guaranteed-to-work last resort based on an actual published known issue with 3.20 that a later version specifically fixes.

0 Elin W over 5 years ago in reply to Chris Hunt

TI__Genius 14845 points

Hi Chris,

Do you have a LaunchPad? If so, you can test the new image on that before re-programming all your custom boards.

Thanks,
Elin

0 Chris Hunt over 5 years ago in reply to Elin W

Intellectual 945 points

The issue isn't having a board to reprogram, it's the turnaround time of having to swap out the boards that are at the test lab once the problem is identified. And I don't know if you've ever tried to take a project made for a custom board and run it on a Launchpad, but that's far from trivial. Anyway, it turns out the difference may have had more to do with the way they attached the cable for conducted testing. So if you can confirm that both the test mode and application should default to 0 dBm, then I don't think there's anything else to do here.

0 Elin W over 5 years ago in reply to Chris Hunt

TI__Genius 14845 points

Hi Chris,

Sincerest apologies for the delay.

After some digging, it seems like using HCI_EXT_SetMaxDtmTxPowerCmd might help with your issue. Is this something you are using in your code?

Thanks,
Elin

0 Chris Hunt over 5 years ago in reply to Elin W

Intellectual 945 points

We are not. The comments in hci.h say that command only applies to DTM, and when DTM is exited, the transmitter output power setting is restored to the default value of 0 dBm, which matches Marie's reply above. Are you saying that those are both incorrect and the Modem Test commands use the max output power of 5 dBm like DTM even when not in DTM?

0 Elin W over 5 years ago in reply to Chris Hunt

TI__Genius 14845 points

Hi Chris,

Thanks for sharing. Have you made any progress with your issue?

Thanks,
Elin

0 Chris Hunt over 5 years ago in reply to Elin W

Intellectual 945 points

"The comments in hci.h say that command only applies to DTM, and when DTM is exited, the transmitter output power setting is restored to the default value of 0 dBm, which matches Marie's reply above. Are you saying that those are both incorrect and the Modem Test commands use the max output power of 5 dBm like DTM even when not in DTM?"

0 Chris Hunt over 5 years ago in reply to Marie H

Intellectual 945 points

Please stop marking this as "TI Thinks Resolved." It is not. Two different TI employees have given conflicting answers, and I have asked twice now for clarification as to which is correct, the first being over a MONTH ago.

0 Evan W over 5 years ago in reply to Chris Hunt

TI__Mastermind 40650 points

Hi Chris,

Apologies for the delay here.

Chris Hunt said:
So if you can confirm that both the test mode and application should default to 0 dBm, then I don't think there's anything else to do here.

Per our documentation, HCI_EXT_ModemTestTxCmd() will transmit at the maximum power, for the RB, this would be 5dBm. After the test is complete and HCI_EXT_EndModemTestCmd is called, a controller reset will be called and the application will resume the default TX power for your application (whatever you've set it to via the set TX power cmd. Default for the application is 0 dBm.

Please let me know if this answers your main question that i seem to be gathering from this thread. Otherwise, we are happy to answer any more questions with priority.