An RFID tag has an antenna to receive a configuration signal, and a
circuit with a controller that can configure the RFID circuit responsive
to the configuration signal. Configuring is such that the tag
backscatters by impressing data either on the carrier frequency, or on a
subcarrier in addition to the carrier signal, depending on the
configuration signal. In the event of a subcarrier, the tag controller
may optionally further determine a frequency of the subcarrier from the
configuration signal. The tag may then be configured to backscatter
differently, upon receiving a different configuration signal. A
complementary reader transmits the configuration signal, thus imparting
an operating parameter. The reader has an interface to receive an input
indicative of a present geography, and a lookup table for determining an
operating parameter based on the present geography. In one embodiment,
the operating parameter is determined from regulations at that geographic
location.