OBID i-scan
®
Montage / Installation
ID ISC.MAT-B
FEIG ELECTRONIC GmbH
Page 16 of 19
M70101-0e-ID-B.doc
The antenna is sufficiently tuned when the impedance is R = 50
Ω
±3
Ω
and X = 50
Ω
±3
Ω
. After
tuning is complete all system components (RF Reader, any Power Splitter, Multiplexer) should be
connected, see Fig. 13. Connect an SWR meter to the HF Reader output and check the tuning
again.
Fig. 13: Block schematic of HF-Reader with antenna
Retuning the antenna
9. Change the capacitance C
2
in small steps using jumper strip J3 until a minimum is reached on
the SWR meter.
10. Change C
1/1
and C
1/2
in small steps on J1, J2 until a minimum is reached on the SWR meter.
11. Repeat both steps until the SWR is
≤
1.3
Note the following when tuning the antenna:
•
The curve for resistance R has two points where the 50
Ω
line is intersected.
•
For very small values of R (R < 10
Ω
) the capacitance C
2
must be increased or decreased in
large steps.
•
The curve for impedance X also has two points where the 0
Ω
line is intersected.
•
For every change of the capacitances note whether the working point runs in the correct
direction.
•
Increasing the capacitance C
2
shifts the curve (see Fig. 12) for resistance R to the left, and both
intersections with the 50
Ω
line move towards a lower frequency.
•
Increasing capacitances C
1/1
and C
1/2
shifts the curve (see Fig. 12) for the impedance towards
lower values.
•
Changes in the distance from metals, magnetic materials or to the floor detune the antenna
after the fact and must be compensated for after installing the antenna.
