What Is Low Power (Short Range) Radio?

gun cutawayThe terms ‘low power device’ (LPD) and ‘short range device’ (SRD) tend to be used interchangeably to describe limited power equipment that is operated without the need for an end-user license. What range is classed as ‘short’ has not been defined, though many telemetry installations operate using low power devices over kilometres rather than metres.

CEPT/ERC Recommendation 70-03 relating to the use of Short Range Devices uses the following definition:

The term short range device is intended to cover the radio transmitters which provide either unidirectional or bidirectional communication and which have low capability of causing interference to other radio equipment. SRD’s use integral, dedicated or external antennas and all modes of modulation can be permitted subject to relevant standards.
Due to the many different services provided by these devices, no description can be exhaustive. However, the following
categories are amongst those covered:

  • Telecommand and telecontrol
  • Telemetry and remote metering
  • Alarms
  • Speech & video
  • RFID
  • Building automation
  • Medical implants
  • Automotive and other radio sensing

Maximum power ranges up to 500 mW at VHF/UHF: with certain microwave/Doppler devices it is higher. Higher limits are allowed for RF identification tags in the 865 - 868 MHz band but are subject to restrictions on installation. Power limits are set for specific applications in specific frequency bands. Different rules have traditionally applied in different countries, but within CEPT Administrations (including all those in the EU) the process of spectral harmonisation is progressing. Currently the harmonised frequencies include 433MHz (general, including radio-activated car keys), 863-865MHz (audio), 868-870 MHz (general, including alarms) 870-915 MHz and 2.4-2.483GHz (WLAN’s, video scanning, etc.).