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ISM 433/868
433 MHz-Band
The 433 MHz-ISM-band covers the frequency range from 433.05 up to 434.79 MHz. It has already been used for a long time to realise customer-specific communication solutions for short and middle distances. With a transmit power up to 10 dBm one can achieve a coverange of several 100 m (open air conditions). In principal the modulation is not predefined. For simple applications AM is chosen, for more ambitious applications FM will be preferred. The only postulation for 433 MHz equipment is the CE sign.
There are no additional limitations concerning the allocation of the availible bandwidth or time resources. So on the one hand you are allowed to perform a continuous transmission, on the other hand you have to deal with high noise levels caused by other 433 MHz-equipment. A safe data transfer can only be achieved over small distances or using powerful channel coding techniques. The usage of the 433 MHz-band demands a profound analysis of possible noise sources and of the requirements given by the application. If these requirements are met, the 433 MHz-ISM-band provides a cheap and easy way to establish a transmission.
868 MHz Band
The regulations for the 868 MHz band are more restrictive than those for the 433 MHz band. So there are less problems with interference. The band is divided into several sub-bands, which are reserved for particular occupancies:
| sub-band | usage | channel grid | duty cycle |
|---|---|---|---|
| 1 | common | broadband | < 1% |
| 2 | alarm | 25 hHz | < 0.1% |
| 3 | common | broadband | < 0.1% |
| 4 | alarm | 25 kHz | < 0.1% |
| 5 | free | ||
| 6 | common | 25 kHz / broadband | < 10% |
| 7 | alarm | 25 kHz | < 10% - 100% |
| 8 | common | broadband | < 10% - 100% |
Dependent on the sub-band the transmission power is limited to 10 dBm … 27 dBm. The permitted time allocation (duty cycle) also varies with the sub-band. So interferences with other 868 MHz equipment are reduced and thus a better transmission quality can be achieved.
CE Sign
The putting into circulation of equipment, which uses an ISM band, requires a declaration of the conformity with all applicable regulations. The conformity is signalised by the CE sign.
In collaboration with an EMC-lab, iaf provides consulting concerning the CE certification and the required measurements. We offer support in analysing the technical problems, if the limitations are not met. Furthermore we revise your design using modern engineering methods.