BLE Link Drops When Body Blocks Line-of-Sight Between nRF52840 Devices

[Andrea Verdecchia]

I’m writing this post because I’m experiencing a problem with data transmission between two devices—a sensor and a USB dongle connected to a PC—each equipped with a Minew BLE module based on the nRF52840. I’ve noticed that as long as I’m indoors, data transmission appears problem-free, but when I move into an open area, the link drops as soon as my body comes between the two devices. Specifically, if I stand facing the USB dongle and place the sensor behind my back, the data stream stops immediately, even when the devices are only about two meters apart.

I know that the human body is a significant obstacle for 2.4 GHz waves, but I didn’t expect attenuation to be this severe. Indoors the issue doesn’t occur, presumably because there are plenty of surfaces that can reflect the signal. I’d like to ask whether communication between two devices can really be disrupted so easily by the human body, or whether I should dig deeper to determine if it’s a board-level design problem (e.g., interference in the transmission caused by unintended emissions from the circuit).

[Amanda Hsieh]

Hi, 

Yes, communication between two devices using nRF52840-based modules can be easily disrupted by the human body, particularly at the 2.4 GHz frequency. Human tissue significantly attenuates 2.4 GHz signals, a limitation well-documented in Taking a deeper dive into Bluetooth 5. It noted that "the only major obstacle usually being the human body (although that is a considerable obstacle at 2.4 GHz)," which is why most Bluetooth applications are limited to around 10 meters in range.

Indoors, reflections off walls and objects can help maintain signal integrity even when obstacles are present. However, outdoors, where reflective surfaces are minimal, the signal is more likely to be blocked when the human body is between the devices.

Your observation that the link fails immediately when your body obstructs the path, even at close range, aligns with typical 2.4 GHz propagation behavior. This is a known physical limitation of the frequency band, but it is not necessarily an issue with your board or design. If performance is acceptable indoors but unreliable outdoors under these conditions, the likely cause is the absence of multipath reflection, not faulty hardware.

Regards,
Amanda H.