This article covers the following topics:
The frequency carrier, as laid down in the KNX Specifications, is 868.3 MHz. Although the specifications also contemplate the possibility to support more frequencies (433.5 MHz and 915 MHz), the current certified system components are only designed for 868 MHz. band. If a KNX Member wished to develop KNX RF devices with other frequency carrier, first the physical layer to be used by those devices must be certified.
Within the current frequency (F1) for KNX RF, 2 different approaches can be found:
KNX RF Ready
- Single channel: same scan frequency = F1
- Longer preamble
KNX RF Multi
- Multiple channels
- Have a 'RF Ready mode' feature onboard. RF Multi devices recognize RF Ready devices.
- 3 fast scan frequencies = F1 (same as above), F2, F3. These fast channels are used for operations that required fast operation/feedback (i.e. shutters controllers).
- 2 slow scan frequencies = S1, S2. These slow channels are used for operations that do not require instant operation/feedback (i.e. temperature measurement for HVAC purposes). The main advantage is the lower consumption, hence these slow channels are more suitable for Energy Harvesting devices, as well enhances the battery life of battery-dependent devices.
ETS does not currently support KNX RF Multi
As for the communication, it can be bidirectional or unidirectional, with some specific requirements. Devices that are designed to work as unidirectional at runtime (i.e. Energy Harvesting devices), must be able to communication bidirectionally during the configuration procedures.
Communication between RF devices is rated based on the transmission quality, based on information divided over two (Medium Object) properties:
- 'filter table': mapping between Individual Addresses & quality table entries
- 'quality table': min/max/average link quality (in dB)
In KNX RF S-Mode devices, communication between ETS and the KNX RF device during configuration can be carried out as follows:
- Using a direct USB-RF dongle, which allows ETS connect with the RF domain and configure the existing KNX-RF devices.
- Using a TP-RF media coupler, so that ETS can be connected to the KNX-TP installation via a KNX-USB connector (or, alternatively, via a KNX-IP Interface or Router, which is connected to the TP installation).
As for runtime, KNX-TP devices can communicate with KNX RF devices thanks to TP/RF media couplers.