User Manual

April 1999 Associated Antenna Systems
29
When low field strength for larger antennas is necessary (Vpeak <60 V), the
antenna resonator can additionally be damped by connecting an onboard damping
resistor, which may be done by closing jumper JP3 (see Figure 3). This jumper is
open by default.
CAUTION: Only a certain maximum antenna resonance
voltage is allowed for this option. Please refer to Chapter
2.1, Recommended Operating Conditions, for details.
Note: The transformer of the transmitter power stage is operated at a
high magnetic flux. Due to the high level of magnetic flux change, the
transformer may emit an audible tone. This may also occur with
antennas that have ferrite cores (e.g. TIRIS Standard Stick Antenna
RI-ANT-S02). This tone does not indicate a malfunction.
4.2 Antenna Resonance Tuning
In order to achieve a high charge-up field strength, the antenna resonator
frequency must be tuned to the transmitter frequency of 134.2 kHz. This is done by
changing the capacitance of the antenna resonator.
To compensate for the tolerances of the antenna coil and the capacitors, six binary
weighted tuning capacitors (C_ATC1 to C_ATC6) have been included. Their values
are weighted in steps of 1, 2, 4, 8, 16 and 32, where C_ATC1 has the smallest
value corresponding to the factor 1, C_ATC2 has double the capacity of C_ATC1,
so that C_ATC2 corresponds to the factor 2 and so on. Each of the 6 tuning pins
has an adjacent ground pin for antenna tuning, using shorting bridges (jumpers).
Monitoring of the correct antenna resonance tuning can be performed using the
Antenna Tuning Indicator (ATI) tool RI-ACC-ATI2.
This device allows the transmitter to be operated in pulsed mode, independently of
the Control Module. It indicates by LEDs whether the tuning capacity should be
increased or decreased (marked on the ATI as IN for increase and OUT for
decrease) and when the antenna is tuned to resonance, in which case the green
LED is on or flashing together with the IN or OUT LED. The device is plugged into
the RFM connector J2 during the tuning procedure, power being supplied from this
module.