Physical Principles of RFID Systems - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 102

Table 4.4 Typical relationship between range and bandwidth in 13.56 MHz systems. An in-
creasing Q factor in the transponder permits a greater range in the transponder system. However,
this is at the expense of the bandwidth and thus also the data transmission speed (baud rate)
between transponder and reader

System Baud rate f Subcarrier f TX Range

ISO 14443 106 kBd 847 kHz 13.56 MHz 0 - 10 cm

ISO 15693 short 26.48 kBd 484 kHz 13.56 MHz 0 - 30 cm

ISO 15693 long 6.62 kBd 484 kHz 13.56 MHz 0 - 70 cm

Long-range system 9.0 kBd 212 kHz 13.56 MHz 0 - 1 m

LF system − 0 - 10 kBd No subcarrier < 125 kHz 0 - 1.5 m

V +

N 1

−

Reader coil

+

R 1

Test transponder
coil

V − V T V

Wave-form generator

∼ d

V R

f 0 = 125 kHz

Figure 4.45 Measurement circuit for the measurement of the magnetic coupling coefficient k .
N1: TL081 or LF 356N, R1: 100 - 500 (reproduced by permission of TEMIC Semiconductor
GmbH, Heilbronn)

Furthermore, the software necessary to calculate a numeric simulation is often unavail-
able — or it may simply be that the time or patience is lacking.
However, the coupling coefficient k for an existing system can be quickly determined
by means of a simple measurement. This requires a test transponder coil with electrical
and mechanical parameters that correspond with those of the 'real' transponder. The
coupling coefficient can be simply calculated from the measured voltages U R at the
reader coil and U T at the transponder coil (in Figure 4.45 these are denoted as V R
and V T ):

L R
L T

U T
U R ·

k = A k · ( 4 . 56 )