Bluetooth radio tests gives 2.0GHz + channel*channelwidth

[Sverre]

When performing pre-qualifying Bluetooth radiotest of our hardware (utilizing the nRF52840-chip) at NEMCO, we experienced very strange behavior. The frequencies detected in the test-chamber was not in the range 2400MHz - 2480MHz as we would expected, but rather in the range 2000MHz - 2080Mz. Is there anyone who can explain this behavior or have any hints on how to utilize the correct frequencies.

Here is the code we used to prepare the nRF5240 for this constant carrier TX test:

static void nrfTxConstantCarrier( uint8_t outputTxPower, uint8_t bitrate, uint8_t channel)
{
nrfRadioDisable();
NRF_RADIO->SHORTS = RADIO_SHORTS_READY_START_Msk;
NRF_RADIO->TXPOWER = (outputTxPower << RADIO_TXPOWER_TXPOWER_Pos);
NRF_RADIO->MODE = (bitrate << RADIO_MODE_MODE_Pos);
NRF_RADIO->FREQUENCY = channel;
#ifdef NRF51
NRF_RADIO->TEST = (RADIO_TEST_CONST_CARRIER_Enabled << RADIO_TEST_CONST_CARRIER_Pos) \
| (RADIO_TEST_PLL_LOCK_Enabled << RADIO_TEST_PLL_LOCK_Pos);
#endif
NRF_RADIO->TASKS_TXEN = 1;
}

And here are some pictures from the test:

[Håkon Alseth]

Hi,

 

It looks like the external clock source is not turned on before running the carrier test, which means that the radio is sourced by the internal 64M RC oscillator.

Could you ensure that the external HFCLK is running?

NRF_CLOCK->TASKS_HFCLKSTART = 1;

while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);

Kind regards,

Håkon