Specifications

5.1. INTRODUCTION
Passive Active
Tag power source External RF field Self-contained(battery)
Memory capacity Less than 128B Over 128kB
Cost Low High
Range Short (up to 3m) Long (up to 100m)
RF field power High Low
Efficiency Low High
Read speed Slow Fast
Multiple tags Poor, slow, unreliable Fast, reliable
Lifespan Long Limited by power supply
Tag size Limited by antenna s ize
Limited by antenna
and power source
Table 5.1: Active vs Passive Tags
and flesh. It is thus ideally suited to animal tracking as tags can be embedded
under the animal’s skin.
High frequency devices offer improved efficiency and performance in open-
air environments. Standards include frequencies of 13.5MHz, 433MHz, 868MHz,
915MHz and 2.4GHz. Higher frequencies (2.4GHz and above) require line-
of-sight links between the tags and the readers. This drawback has limited
these systems’ penetration into the RFID market.
5.1.4 Modulation and Encoding Schemes
Early tags adopted amplitude shift keying (ASK) as it was simple to implement
and resulted in cheaper tags. However, noise-immunity is poor and most
low frequency tags now use frequency- (FSK) or phase shift keying (PSK).
Encoding techniques (such as NRZ or Manchester encoding) are sometimes
used, however, to keep complexity of the tags at a minimum, many low-cost
FSK devices simply transmit the raw bit stream using two frequencies - one
to represent a logic “1” and another to represent a logic “0”. ASK is still
common in high-frequency transponders.[7]
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