Tuning Procedure - Texas Instruments 2000 Series Reference Manual

High Performance RA-RFM RI-RFM-008B

4.3 Tuning Procedure

The following notes refer to antenna resonance tuning in general:
Note:
If an antenna has to be installed in an environment where metal is
present, the tuning of the antenna must be done in this environment,
since the presence of metal changes the inductance of the antenna. In
addition, the Q factor of the antenna decreases, thereby decreasing
the field strength. The extent of the inductance and quality factor
reduction depends on the kind of metal, the distance of the antenna
from it and its size.
When the oscillator signal pulse width, or the supply voltage VSP of
an RA-RFM with a pre-tuned ferrite core antenna (for example: RI
ANT S02) is changed by a factor of more than 50%, the ferrite core
antenna has to be re-tuned to the new conditions due to the
inductance changing slightly at different field strengths.
Each antenna is tuned individually to the RA-RFM and this results in a
unique tuning jumper arrangement for this combination of antenna and
RA-RFM.
If a different antenna or RA-RFM is connected, the new combination
must be tuned to resonance again.
1. Switch RA-RFM power supply off.
2. Calculate the required resonance capacitance (see calculation method below).
3. Set the tuning range jumper on the Antenna Tuning Board which is closest to
the calculated value according to Table 15.
4. Connect the Antenna Tuning Board via twin-ax cable to the RA-RFM via the
ANT1 connector.
5. Connect antenna tuning monitor (oscilloscope or voltmeter).
6. Switch RA-RFM power supply on.
7. Tune the antenna to maximum by adjusting the series coil on the Antenna
Tuning Board.
8. If this is not successful, retune the antenna to maximum by changing the tuning
capacity one level up or down and then repeating step 7.
9. If this is still unsuccessful, check the calculations and repeat the process from
step 1.
The antenna resonance tuning is now complete.
34
February 2002