RE: How to reduce the range of bluetooth signal?

Einar Thorsrud — Fri, 01 Jun 2018 07:36:12 GMT

Hi,

Any of the nRF5x devices can be used to make a beacon such as you describe. The nRF52810 is perhaps most suitable for a simple beacon.

There are many factors that affect range, so you cannot configure it very precisely. Particularly, the sensitivity of the peer device and the RF environment is typically out of your control. However. What you can do is to adjust the radiated power. The most important factors to consider for range are:

Transmitter power out of the nRF, which can be adjusted in the nRF.
Loss due to antenna matching, housing etc. on the nRF side.
The free space path loss. This is ~40 dB at 1 meter, and you can add ~6 dB per doubling of the distance (e.g. 46 dB at 2 meters).
Receiver sensitivity. This can vary significantly between different peer devices, so the range will vary accordingly.

Example:

Configure the nRF52 output power to -20 dBm (lowest possible is -40 dBm).
Let's then say that the HW in sum has a loss of 10 dB, then the radiated power will be -30 dBm.
Then let's say the peer device has a practical sensitivity of -80 dBm (just to pick a number).
In this case, the peer can receive the signal if the path loss is < 50 dB (80-30), which correspond to a distance of approximately 3 meters.