Unexpected 2.4 GHz Emissions During EMC Testing (RADIO Supposed to Be Disabled) nRF52840

[enukic]

Hi,

I'm working on a product that uses nRF52840 (The custom board actually has the Ebyte module E73-2G4M08S1C).
nRF5 SDK 17.1.0.

The firmware consists of:
1. Bootloader - Derived from pca10056_usb example bootloader (minimal changes, in sdk_config.h only

2. Main app - Derived from usbd_hid example.

The final firmware image doesn't contain a Softdevice.

The main app firmware uses following peripherals:
- SAADC with TIMER + PPI for ADC sampling
- RTC for app_timer
- GPIOTE for two button inputs
- PWM for RGB LED control
- USBD for USB communication with a PC

Importantly, the application does not use the RADIO at all. Since the product is currently undergoing EMC certification, we want to ensure there are no 2.4 GHz emissions.

To guarantee that the RADIO stays off, we added this line at the very beginning of main.c:

NRF_RADIO->POWER = 0;



However, measurements from the EMC lab show clear emissions in the 2.4 GHz band. I’ve attached the spectrum analyzer results.

What could be causing the RADIO to emit in this configuration? Could the bootloader or another component be unintentionally enabling BLE or otherwise activating the RADIO?

Any guidance on how to fully disable the radio functionality for certification would be greatly appreciated.

Emir

[Asbjørn]

Hello Emir,

Q1: Just to be sure, these emissions disappear if you remove battery or voltage to the board? So you are sure it is coming from your board?

Q2: If you unplug the USB, does it stop then?

You have switched off the radio with your configuration, so there shouldn't be anything from the nRF52840 unless you somewhere else enable it again unintentionally? 

This screen shot doesn't really look like nRF/BLE activity. It looks a bit more like WiFi channels, but it is difficult to say for sure. If you do not enable the radio, there won't be any transmit or activity in the band. 

In the E73-2G4M08S1C, does it come with some BLE features enabled? Is there a built in bootloader in the module or is it completely empty flash?

Best regards

Asbjørn

[enukic]

Asbjørn 
Thank you for your response.
As it turns out the lab made an error, and as the result of this error spectrum analyzer pricked up some environment signals (probably WiFi).

This ticket can be closed.

Thank you
Kind regards
Emir