OBID i-
scan
®
Installation
ID ISC.MAT-A
FEIG ELECTRONIC GmbH
Page 20 of 28
M21200-0de-ID-B.doc
E N
G
L I S H
8. Installation and wiring
8.1.Determining the resonance capacitances
The tuning circuit with antenna conductor can be represented as below:
Fig. 7 Equivalent circuit diagram of the antenna
To calculate the capacitances you must first measure the inductance of the antenna conductor.
This depends mainly on the cable length, antenna shape and the antenna conductor itself
(diameter, shape). The inductance of the antenna cable should be measured in an environment
similar to where the antenna will be operated (distance from metal and floor).
The antenna Q is set using resistor R
R
before tuning, using jumpers set to 0, 1, 2 or 3
Ω
. The
series resistors R
1
= 1
Ω
and R
2
= 2
Ω
can be jumpered using J1 and J2.
The antenna Q has an affect on the antenna current, the bandwidth and the sensitivity of the
antenna to changes in the environment. It depends on the desired read range and national RF
regulations. The standard setting is 2
Ω
.
When a quadratic antenna is used, the approximate inductance can be determined from the
following table (approximate values).
C
1
R
R
L
p
C
2,1
C
2,2
Tuning circuit
Antenna conductor
J1
J2
1
Ω
2
Ω
