short range device (SRD)
SRD (Short Range Device) technology is a short-range radio for distances of a few meters. SRD technology is used, among other things, in wireless mice, remote controls for televisions or audio systems, in central locking systems for vehicles, monitoring modules for automotive components, in telemetry for wireless sensors, in telecontrol technology and in alarm systems.
The Short Range Device is a radio technology that can be used by the general public without registration or licensing. Because SRD devices operate at relatively low transmit power( EIRP), these devices also have the designation Low Power Devices( LPD).
SRD technology uses several license-free frequency bands, primarily the ISM bands. The usable frequency bands and the permissible transmission power have been defined by the RegTP. These are the frequency bands at 433 MHz, 868 MHz, 902 MHz, 2.4 GHz and 5.7 GHz. In addition, further frequency bands are to be released in the frequency range between 40 GHz and 50 GHz. In the frequency range between 433.075 MHz and 434.775 MHz alone, 69 channels are available in a frequency grid of 25 kHz. With a transmitting power of 10 mW and a prescribed frequency modulation, distances of up to 3 km can be bridged under good topographical conditions.
SRD systems normally operate unidirectionally, they have no return channel over which the executed control function could be confirmed. Function execution can only beverified by visual inspection.
However, there are also applications where visual control is not possible, such as alarm systems or telemetry applications. This is where error correction methods can come in.