Modulation scheme for nRF52840 radio transmission

[TigerD]

Hi,

I have nRF52840 DK boards.

This is rather an informational question for my benefits.

In post:  https://devzone.nordicsemi.com/f/nordic-q-a/9315/nrf52-802-15-4

   "With BLE and with nrf5x chips the modulation scheme used is Gaussian frequency shift keying (GFSK)"

My understanding is modulation GFSK is implemented in nRF52 chips as hardware layer. It is not optional. But why in the radio test examples,

      cmd_tx_carrier_start(nrf_cli_t const * p_cli, size_t argc, char ** argv) {

            ...

           m_test_config.type                          = UNMODULATED_TX;

            ...

      }

It includes a test configuration with UNMODULATED_TX?

Did I miss anything?

Thank you,

David Zhou

[Marjeris Romero]

Hi David,

Bluetooth LE uses GFSK as the modulation scheme. nRF52811, nRF52833, nRF52840 and nRF5340 also support 2.4 GHz IEEE 802.15.4, which uses O-QPSK modulation scheme at 250kpbs.

Support for a given modulation scheme is added in the PHY later, but which modulation scheme to use is optional.

Our radio test example focus on testing the radio PHY so it gives you command line interface commands for setting output power, modulation scheme, modulated or unmodulated carrier, rf channel and other parameters. For radio certification you will usually need to be able to set up a constant unmodulated TX carrier at a fixed frequency.

In the radio test example you can choose between:

start_tx_carrier		Start the TX carrier.
start_tx_modulated_carrier	<packet_num>	Start the modulated TX carrier (continuous TX mode is used if no argument is provided).

The unmodulated carrier is used mostly for testing, as you can't convey information without a modulation scheme.

Best regards,

Marjeris

[TigerD]

Thank you, Marjeris.

David