User Manual

High Performance RFM RI-RFM-007B April 1999
38
3. Supply voltage of the RFM power stage.
The higher the supply voltage of the RFM transmitter power stage (VSP voltage),
the higher the field strength which is generated by the RFM assuming that all other
parameters remain unchanged. However, the generated field strength does not
increase linearly with VSP supply voltage. In addition, ferrite core antennas show
saturation effects (saturation means here that the ferrite core cannot generate
more magnetic field strength, even with a higher input current).
4. The oscillator signal pulse width.
The bigger the selected transmitter oscillator signal pulse width, the higher the
magnetic field strength which is generated by the RFM, since more power is fed
into the antenna resonator by the transmitter power stage assuming that all other
parameters remain unchanged.
The generated field strength can be measured in several ways. It may be
measured using a calibrated field strength meter or by measuring the antenna
resonance voltage using an oscilloscope and then calculating the field strength.
In summary: the generated field strength of an antenna can be adjusted with the
supply voltage VSP of the RFM transmitter power stage and by selecting the
corresponding oscillator signal pulse width.
In cases where low field strengths should be generated with large antennas (RI-
ANT-G01 and RI-ANT-G03), the antenna resonator can be additionally damped by
closing jumper JP3.
Using this optional damping function allows the field strength to be again fine-tuned
to meet FCC/PTT regulations with selection of the oscillator signal pulse width in a
wide range of both larger and smaller values.
CAUTION: This damping option can only be used together
with the TIRIS standard antennas RI-ANT-G01 and RI-ANT-
G03. Only a certain maximum antenna resonance voltage is
allowed for this option. Please refer to Section 2.1,
Recommended Operating Conditions, for details.
Note: For correct adjustment of field strength according to FCC/PTT
values, especially for customized antennas, a calibrated field strength
meter must be used. Field strength measurements must be taken on a
free field test site according to VDE 0871 or equivalent regulation.