SRD Short Range Devices
- essential information and details of SRD Short Range Devices, what they are, the regulatory aspects and how a Short Range Device may be used.
SRD, Short Range Device is a term that is applied to a radio or wireless device that is designed to operate over a short range. This also implies that the power levels are low and hence the likelihood of interference to other devices is low. This enables SRDs, Short range Devices to be operated under relaxed regimes of regulation, which are often termed "licence free."
In general, the term SRD or Short range device refers to a variety of short range transmitter receiver systems that have power output levels of less than a watt, with most falling below 10 milliwatts. As a result their range is limited, most operating at ranges well below 1 km. Data rates can vary considerably, ranging from a rates in the region of 100 bps to as high as 1 Mbps and more. These levels of functionality are ideal for many applications where short ranges are needed along with proprietary radio technology.
SRD, Short Range device applications
Short Range Devices may be used in a large variety of applications where low power transmission of data is needed over short distances. In many instances the use of an existing standard such as Wi-Fi or Zigbee may not be appropriate as it may require a large overhead in terms of formatting the data for the particular standard. In these cases a standard alone solution may be more appropriate. Accordingly specialized SRD, Short Range Devices may be more appropriate.
There are many applications for which short range devices are used. These include applications like those listed below:
- Garage door and gate controls
- Alarms and movement detectors
- Industrial control
- Industrial monitoring
- Anti-theft devices
- Low rate data transmission
- RF identification (RFID)
The regulations for Short Range Devices, SRDs vary according to the country in question.
One of the main areas where care has to be taken when using SRDs is to ensure that the frequencies used match those of the particular region in question. A wide variety of frequencies an bands are available, although some are only available in particular countries as shown below:
|Band (MHz)||Region and Comments|
In these bands the regulatory authorities allow suitably approved and tested radios to be used without the need for individual user licenses.
International SRD standards
As it is inevitable that SRDs will be used in many countries around the world, it is essential that international standards are adopted for these devices. A variety of standards have been developed for different types of SRD.
|EN 300 220 ||ETSI ||This standard covers SRD equipment operating in the frequency range 25 MHz to 1000 MHz.|
|EN 300 330 ||ETSI ||This ETSI standard covers SRD radio equipment operating in the frequency range 9 kHz to 25 MHz (and inductive loop systems operating up to 30 MHz).|
|EN 300 440 ||ETSI ||This covers SRD radio equipment operating in the frequency range 1 GHz to 40 GHz.|
|Chapter 15 part 247||FCC ||This SRD definition is primarily used for devices for North America.|
 These standards are each in two parts designated EN 300 xxx-1 or EN 300 xxx-2. Part 1 covers technical requirements, including those for specific applications. Part 2 is the Harmonized Standard, which identifies the necessary parameters to comply with article 3.2 of the R&TTE Directive
 ETSI is the European Telecommunications Standards Institute.
 FCC is the Federal Communications Commission.
Although there have been many attempts to harmonise standards across the globe there are still many variations. Most of Europe, Africa and Australia use systems based on the ETSI standards, whereas USA and Canada have those based on the FCC standards.
SRD EMC considerations
One area that is particularly important where unlicensed transmitting devices are concerned is that of EMC. It is necessary to ensure that these SRDs do not radiate unwanted transmissions that may cause interference to other users.
As a result of this requirement, ETSI has produced standards that specify the Electromagnetic Compatibility or EMC requirements. For short range devices, SRDs, the relevant ETSI EMC standards are:
- EN 301 489-1 (Common technical requirements for radio equipment)
- EN 301 489-3 (Specific conditions for SRDs)
Short range Devices, SRDs are used for many wireless or radio applications where only limited ranges are needed. Often small data transmission devices conforming to the relevant specification provide low cost but effective solutions enabling data to be transferred over a radio link. While standards such as 802.11, 802.15 and other specifications are ideal for many applications, SRD short range devices may be used for many other specific applications where data needs to be transported over short distances. The short range devices, SRDs using proprietary radio designs do not have the overheads of the protocol stack and high degrees of conformance testing required for standards such as Zigbee, Bluetooth, etc. Accordingly SRD developments may be the ideal path for many applications.
By Ian Poole
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