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4 4 .7
Planning and installation of UHF read points
Due to their comparatively large effective range, RFID UHF systems (frequency band 865 -
928 MHz) have different requirements in terms of planning, commissioning and operation
compared with the HF systems commonly used up to now in automation (frequency band
13.56 MHz). This section describes important rules for preparation and implementation of the
RFID UHF systems.
4.7.1
Technical basics
General
In contrast to inductively coupled HF systems, in UHF technology, there is full propagation of
the radio waves just as in other wireless systems (radio, TV etc). There are both magnetic
and electrical field components present. The following graphic shows the structure of a UHF
system. One characteristic is the design of the transponder that differs greatly from the
structure used in HF systems, e.g. the use of a dipole or helix antenna.
Figure 4-14
RSSI value
The signal strength of the transponder response is known as the RSSI value (Received
Signal Strength Indicator). The RSSI value is a one byte value (0 to 255), the higher the
value the better the signal strength (according to the IEEE 802.11 standard).
The actual RSSI value depends on numerous parameters:
SIMATIC RF600
System Manual, 06/2019, J31069-D0171-U001-A22-7618
Structure of a UHF RFID system
transponder type used,
chip used in the transponder,
connected antenna,
transmit power,
4.7 Planning and installation of UHF read points
RF600 system planning
69
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