Antenna Requirements - Texas Instruments 2000 Series Reference Manual

High Performance RA-RFM RI-RFM-008B

4.1 Antenna Requirements

Parameter
L_ANT Antenna inductance range within which the antenna can be tuned to
resonance
Q_ANT Recommended Q factor of antenna coil for correct operation
In order to achieve high voltages at the antenna resonance circuit and thus high
field strength at the antenna for the charge-up (transmit) function, the antenna coil
must be high Q. The recommended Q factor for proper operation is listed in Table
14, Antenna Requirements. The Q factor of the antenna may vary depending on
the type, the construction and the size of the antenna. Furthermore, this factor
depends on the wire type and wire cross-sectional area used for winding of the
antenna.
RF braided wire, consisting of a number of small single insulated wires is
recommended for winding of an antenna since it gives the highest Q factor and
thus the highest charge-up field strength, for example single wire diameter of 0.1
mm (4 mil) and 120 single insulated wires.
Note:
If a high Q is not required (for example for large in-ground antennas),
standard braided wire can be used.
In order to ensure that the transmitter and receiver function correctly, the antenna
must be tuned to the resonance frequency of 134.2 kHz. For a detailed description
of the antenna resonance tuning procedure, refer to the next section, Antenna
Resonance Tuning.To ensure that the antenna can be tuned to resonance with the
Antenna Tuning Board, the antenna inductance can only vary within the limits
given in Table 14.
Table 14: Antenna Requirements
Conditions
Note:
Although a ferrite core antenna may have a high Q factor under test
conditions with low magnetic field strengths, the Q factor decreases
when a high magnetic field strength is applied to the ferrite core.
WARNING:
CARE MUST BE TAKEN WHEN HANDLING THE RA-RFM.
HIGH VOLTAGE ACROSS THE ANTENNA TERMINALS AND
ALL ANTENNA RESONATOR PARTS COULD BE HARMFUL
TO YOUR HEALTH.
DAMAGED THE ANTENNA SHOULD NOT BE CONNECTED
TO THE RA-RFM.
IF THE ANTENNA INSULATION IS
32
February 2002
min. typ. max. Unit
µH
8 27 80
40 450 -