to the reader 12 or to a third party processor for determining the location of the passband window 26 as shown in the graph illustrated in fig3 the passband window 26 may be optimally located based on the ambient pressure measured by the reader 39 s ambient pressure sensor 25 for example in an embodiment where the sensor is a wireless pressure sensor implanted in the pulmonary artery of a human being the pressure range of interest is 0 100 mmhg above ambient therefore the reader 39 s processor would be programmed to locate a passband window 26 such that its edges are at frequencies corresponding to the ambient pressure reading and a pressure that is 100 mmhg greater than the ambient pressure reading as shown in fig3 accordingly the reader 12 may tune its antenna 24 as well as its internal circuits and algorithms to focus the passband window 26 near the ambient pressure in an embodiment a wireless sensor 14 may be implanted into a human being located at relatively high altitude for example an altitude having an ambient pressure near 630 mmhg absolute the pressure range of interest may therefore be 630 730 mmhg absolute corresponding to a frequency passband window 26 of 13 831 13 546 mhz the reader 12 may measure the ambient pressure using its ambient pressure sensor 25 the reader 12 may then determine from the ambient pressure measurement the subset of the full scale frequency range that will contain.