I’m using the term loosely, and in the broadest possible way: human, the board, and other devices.
The board is designed to radiate radio waves- albeit at a very low power.
However, every doubling in distance from you and the antenna reduces the field strength by half, and the power by a quarter.
More accurately, I believe this is correct for the far field. Antenna propagation is complicated, with some unusual things happening close to an antenna. According to the near and far field calculator at everythingrf.com, the far field starts at ~5cm for a 915MHz signal and a 10cm antenna. So if you’re concerned, keep it further than 5cm while transmitting, 10cm to halve the intensity (quarter the power), etc.
Other Device Safety
It’s hard to develop perfect software! Even if we don’t intend to transmit, we might accidentally tell it to send a message.
These boards are made to work in different parts of the world, which have different frequency ranges for use by WiFi, BlueTooth, LoRaWAN and other non-licensed transmitters. (Not requiring the operator to have a license- they are still required to be certified.)
As such it’s always good practice to make sure any frequency ranges are configured for the jurisdiction you’re in!
i.e. how to keep the "magic smoke" in the chip!
- it can be damaged by static electricity
- it’s a 3.3V (or 3V3) device; don’t plug it into 5V circuits
- except the USB socket– there’s a regulator that onboard that will convert the USB 5V supply to 3V3.
- U.FL connectors are not super strong
- suggest carefully clipping on the pigtail for the antenna and leaving it attached. Can unscrew the helical antenna for storage
- RF waves REFLECT when there’s not an antenna
- think of a string tied to a solid wall, to which you apply a wave… does it stop, or bounce back at you
- end of the PCB/conductor is like that wall
- reflected power back into the transmitter can cause it to heat up and/or damage it