Compliance Assessment of a RWCL-0516 Doppler Radar Motion Detector

I’ve been helping a customer out with some EMC pre-compliance testing of their new domestic product which included a range of 3rd party modules.

One of these modules was an “RCWL-0516” 3GHz radar for motion detection. These modules are widely available but technical information is mostly reverse engineered by enthusiasts and hobbyists. The best collection of information seems to exist on this GitHub page.

RCWL-0516 - board image from github.com-jdesbonnet

The customer was very keen to use these devices but making some measurements and looking into the regulatory side meant that it got a Big Fat No from me.

 

EMC Radiated Emissions

Radiated emissions in the 1-6GHz band were in excess of the Average limit line by over 17dB.

RCWL-0516 - radiated emissions Class B domestic

This is normally OK for a radio system, as exceeding these limits is often required to achieve the desired range and operation. However this only works if there is a counter-part radio standard to refer to…

 

Analysis of the Regulatory Status of this device

  • No CE / UKCA marking applied to these devices – should not be sold in the EU / UK
  • No CE / UKCA marking Declaration of Conformity supplied by manufacturer – should not be sold in the EU / UK
  • No reference to technical standards used to assess the device to the Radio Equipment Directive
  • At present there are no radio standards published by ETSI for the use of this 3.1GHz band for this kind of application in the EU or UK.
  • This document from CEPT on the use of Short Range Devices gives more details about what radio bands can be used
  • 3.1GHz is not a Harmonised Frequency band. Instead, it is licensed, and operation is only permitted in some countries. The key to the table is at the bottom.

RCWL-0516 - CEPT radio band table

  • Even when taking this table into account, this band is only for UWB Location Tracking Systems.

RCWL-0516 - CEPT radio band table part 2

  • Following the documents further down the chain, the ECC/REC/(11)09 mentioned above refers to two documents:
    • TR 102 495-5 for use of Ultra Wide Band for location tracking operating in 3.4 to 4.8GHz. This device is not UWB and not operating entirely in this band.
    • ECC REPORT 120 requirements for UWB Detect-and-Avoid for operation in this band. This device has not such capabilities.
  • The only way that this radar device can be considered legal to operate is if it meets the Class B (domestic) emissions limits in the 1-6GHz band.
  • Currently this is not the case. With this example product, emissions will need to be reduced by 17dB or more to comply.
  • The oscillator used relies on parasitic components between PCB elements. Tolerance of components, PCB manufacturing tolerance, values over temperature means that frequency stable operation is not practicable.
  • From a regulatory standpoint, these devices should not be touched with a barge pole
  • Other motion detector products exist – I’ve not linked to any as I don’t want to unfairly endorse anything I’ve not investigated further or tested myself.

 

Summary

Anyway, I hope this clears up some of the questions about this device.

I can’t recommend using these devices at all. If you are going to use one of these then keep an eye out for interference with other systems. Don’t even bother if you want to make something that you can sell at the end of the process.

Cheap 3rd party modules like this are usually cheap for a reason.

Thanks to Charlie Blackham for pointing me in the right direction with the radio standards.