The Industrial, Scientific and Medical (ISM) radio bands are not only used for digital communications, but are also open to a myriad of technical equipment that emit energy into them.

ISM diathermy is an example that is used for deep heat treatment of injured muscles and ligaments. ISM machines are also used in industry for quick woodglue drying in boat building, plastic welding and forming in the automotive industry, even biscuit manufacturers use them.

In short, although the radio technologies used in ISM bands are robust and well thought out, they have to compete with applications that frequently put huge amount of energy into the band, creating interference.

Here the IEEE reports:

... the signal activity and power levels are measured in the European Industrial, Scientific, and Medical band 863-870 MHz in the city of Aalborg, Denmark. The target is to determine if there is any interference, which may impact deployment of Internet of Things devices. The focus is on the Low Power Wide Area technologies LoRa and SigFox. The measurements show that there is a 22-33 % probability of interfering signals above -105 dBm within the mandatory LoRa and SigFox 868.0-868.6 MHz band in a shopping area and a business park in downtown Aalborg, ...


We were contacted by a customer and asked to provide a solution to a problem they were having with RF interference in certain installation locations. They wanted to be able to identify and locate sources of interference that were interrupting their RF communications. Price was one of their main constraints and ease of use was important so that the solution could be used by staff  with minimal training. 

The solution consisted of two parts:

  • A radio hardware front end with firmware that was able to capture the RF spectrum data and pass it through a USB interface that linked it to a laptop.
  • A Qt application running in the laptop, that could drive the hardware and made sense of the signals received, running frequency and time domain analysis to identify the interference source.