Radiocommunications Agency  EMC Awareness

Telecommunications

Description

Products are available that 'twinkle' when attached or placed in close proximity to a mobile phone. These products contain one or more Light Emitting Diodes (LED's) that illuminate when the mobile is transmitting. Measurements have shown that these devices have the potential to cause interference to the cellular networks and other users of the radio spectrum. In addition, the mobile phones themselves could experience loss of communications range and the phone battery may need to be charged more frequently.

Any change in configuration of radio transmitting equipment from that which was originally subject to compliance testing is likely to take it out of specification. This is important on two counts. Firstly, the equipment when used is likely to cause interference and not perform to its true potential. Secondly, where equipment no longer performs to the requisite technical requirements, as is clearly the case when a twinkling antenna is fitted to a cellular telephone handset, the apparatus no longer qualifies for licensing.

Commentary

The basic problem here is that the LEDs, powered as they are by the transmitted RF energy, are nonlinear diode devices and so cause intermodulation and harmonic generation from the transmitted frequency. Thus the radiated energy contains frequencies that were not present without the LEDs and which could fall on channels used by other radio services.

References and links

RA Licensing Procedures Manual for Public Wireless Networks Unit, http://www.radio.gov.uk/topics/pmc/document/pwnumanual2/pwnuman2.htm#b1

Links to Mitigation Techniques

	Installation	Design & Development	Resources
Intermodulation