What we do
“Radiometrix is a manufacturer of low power ISM band radio modules”
And that sentence means what ?
There are a very large number of misconceptions to be found when looking at the subject of ‘low power’ or ‘ISM’ radio. To begin with, it’s a very broad categorisation indeed, and also there are the (all too human) attempts by suppliers in this area to push ‘their’ solution as the only one.
In this article maybe I will be able to sort out a few of the confusions.
The terms ‘low power radio’, ‘ISM’ (industrial, scientific and medical) and ‘SRD’ (short range device) has come to refer to a wide class of data communication radios with transmitter output powers of less than 1 watt (most are actually 10mW or less), operating at ranges of less than 500m (although some VHF units can reach over 10km) and a wide variety of data rates (below 100bit/sec, to over 1Mbit/sec). They are used in general data communication, remote control, monitoring and alarm applications. The term ‘telemetry radio’ is also sometimes applied to these devices (wrongly as it happens: ‘telemetry’ actually means ‘remote measuring’ which covers only some of these applications. Many include remote activation, or ‘telecontrol’)
Generally, radios in this class operate in ‘unlicensed’ areas of spectrum, where regulatory authorities allow suitably approved and tested radios to be used without the need for specific individual licenses. Some parts of this spectrum is allocated to ‘general purpose’ usage, while other parts of the band may be restricted to (for instance) alarms, or remote meter reading. Unfortunately, despite attempts to harmonise usage within the EU (and elsewhere) the permissible frequencies avaialble for use, and specific approval standards can vary from country to country. Most of the EU, parts of Eastern Europe, Africa, and Australia have fairly similar regulations (look for the “EN300-220-3” standard approval), but America and Canada are totally different (FCC ‘chapter 15, part 247’ ). A lot of care is needed to select radios for a widely-marketed product.
So what sort of radios are available ? Assigning any absolute categories is full of difficulties so instead we will consider them in terms of typical operating range. (We are considering a likely in-building or urban environment range. Much longer ranges are seen across valleys, over sea, or air to ground. In our experience, any range quoted by a module supplier ought to be distrusted, until actual field trials have been conducted)
- Up to 10 meters. Very different types of radio provide this sort of short range coverage. Basic remote control tasks (toys, desktop gadgets, controls for domestic goods) are typically handled by very simple HF (27 and 40MHz) designs, while high data throughput links (digital wireless audio, computer peripherals, point of sale terminals) use complex integrated circuit solutions, frequently using protocol standards such as Bluetooth in the 2.4GHz band. (this type of radio is being called a “personal area network” device latterly)
- Up to 50 meters. Wireless LAN and other high throughput systems use WiFi or similar in the 2.4 or 5.8GHz bands. Complex mesh-network systems (sensor nwtworks, home automation systems) use ZigBee, or one of the similar near-copies. Simpler one to one, or polled network, data systems, and better quality remote control products use conventional wideband radios in the 433 or 868MHz (915MHz in USA) allocations (either simple modules, or single chip radios)
- Up to 200 meters. Security and alarm systems, vehicle data download. With increase in range the 2.4GHz high data rate radios reach their physical limit. Wideband modules are the more sophisticated types (rather than single chip solutions), and simpler narrow band radios come into use for critical industrial and alarm tasks. High data rate links using 2.4GHz require more complex, fixed directional aerials. (Under the very different US FCC regulations, this market segment is addressed by high power 915MHz spread spectrum radios.)
- Up to 500 meters. Serious industrial control and monitoring, large site alarm systems. High performance, complex narrow band radios dominate, usually multichannel to improve adaptability and allow multiple co-sited systems. Data rates rarely exceed 10kbit/sec. Low power VHF equipment is used (the lower path loss at VHF gives greater range for a given power)
- Over 1km. Long range telemetry and command, remote controlled vehicles, high value asset tags. Only VHF band and the higher powered (500mW) UHF radios will provide good enough link reliability. Specific national regulations become more of an issue (not every country will have a suitable allocation, and sometimes licenced operation is necessary). GSM/GPRS modems compete where good network coverage is available
- Over 5km. Marine data links, agricultural control, irrigation. Of all the unlicensed ISM band radios, only VHF units can offer this range, and only with good aerials, properly placed. At these ranges licensed operation (where much higher transmitter powers are allowed, but often at the cost of more stringent radio specifications such as EN300-113) starts to become economic, as does GSM/GPRS (assuming coverage) or even direct satellite based systems (ARGOS for instance, although operating costs are very high)
Over 5km and we’re well outside the “low power radio” area.