OBID
®
Antenna Manual
ID RW24
FEIG ELECTRONIC GmbH
Seite 5 von 15
h80391-1e-ID.doc
2. Basic factors
2.1. Equivalent circuit diagram
In general, each of the antennas listed in this manual may be illustrated by the equivalent circuit dia-
grams as shown in diagram 2.1-1.
R
Ohm
L
C
W
R
ESB
L
ESB
a)
b)
In this case, the equivalent circuit diagram a) for the actual frequency of 125 kHz may be converted
to the more simple equivalent circuit diagram b). By carrying out this conversion, the parallel capaci-
tor, which is part of a) and describes the external and internal capacitance, leads to an increase in
the resistive and inductive component in b).
As an example, this may lead to the fact that an antenna which is working at an actual frequency of
125 kHz has a higher resistance than at lower frequencies or direct current. Thus, measuring the
internal resistance of the antenna with a multi-meter is only partially useful, since the multi-meter
generally performs direct-current measurement.
The same applies to the equivalent circuit diagram inductance L
ESB
. This value, too is increased by
the parallel capacity C
W
. However, this apparent inductance increase does not lead to a greater
reading range of the reader, since the inductance L, which is effective for communication, is not in-
fluenced. This inductance increase has a rather parasitic effect.
2.2. Admissible antenna parameters for reader model ID RW24
The IDRW 24 is suitable for antennas with an inductance L
ESB
of 600 µH up to 1200 µH. For the
maximum reading range, you have to choose the highest possible inductance for antennas with the
same dimensions. However, 1200µH should not be exceeded. A value of 1100 µH has proven con-
venient.
As far as the resistance R
ESB
is concerned, values between 5
Ω
and 30
Ω
are admissible. However,
the optimal working range lies between 10
Ω
and 20
Ω
. In case that the resistance of the antenna is
less than 5
Ω
or more than 30
Ω
, the output driver of the ID RW24 is working off-specification, which
may lead to a drastical reduction of the reading range.
