Tuning Example Showing Increase Of Total Tuning Capacity And Generated Field Strength (Typical Values) - Texas Instruments 2000 Series Reference Manual

Tuning Procedure
The tuning of a new antenna to the RFM is started with no jumpers (shorting bridges) connected. While
monitoring the resonance condition as described above, the jumpers are plugged in or out, thus
connecting and disconnecting the tuning capacitors in such a way that the total tuning capacity will
increase in steps of the smallest capacitance C_ATC1.
Counting-up of the binary weighted tuning capacitors is in principle done in the following way:
1. No jumpers connected.
2. Connect C_ATC1 (J3 pins 1 and 2).
3. Disconnect C_ATC1 and connect C_ATC2.
4. Connect both C_ATC1 and C_ATC2 (and so on).
However, the tuning steps do not offer an absolutely continuously increasing function, due to component
tolerances. It is therefore possible that when the tuning value is increased by one binary step the total
tuning capacity actually decreases (especially from tuning step 31 to 32), which can result in the
generated field strength not steadily increasing (as shown in
the Antenna Tuning Indicator tool (ATI) since the indicated resonance condition is always correct.
It is therefore recommended to perform resonance tuning according to the flow-chart shown in
50
45
40
35
30
25
20
15
10
5
0
1
Figure 4-1. Tuning Example Showing Increase of Total Tuning Capacity and Generated Field Strength
28 Associated Antenna Systems
'false' resonance
point
Tuning capacity
Field strength
4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61
D e cima l va lue of tuning ste p
(Typical Values)
Figure 4-1). This is not the case when using
SCBU022 – November 2002
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Figure 4-2.