I've been asked to look at developing a simple proximity
detector.  I kinda have in mind using a PIC to pulse a series resonant LC
once per minute or so.  The LC would radiate a damped 49 MHz sine wave
based on its self resonance.  The PIC would just drive this LC with a
step that changes state once per minute or so.
        I need to detect this damped sine wave up to 10 feet away.  I'm
thinking of another LC (probably using circuit board traces for L)
driving a single chip RF amp set up as a Schmitt trigger so it only
detects stuff over a certain level.  This would drive a diode detector
which would then probably drive an analog in on a PIC.  Software would
check the timing of the damped RF pulses to identify the particular unit
transmitting.
        Anyone have experience in this area?  I am somewhat concerned
about the whole thing being jammed by a cordless phone but don't want to
build a superhet receiver to try to get more selectivity.  Perhaps a
ceramic or SAW filter after the LC?  Even then, with shared spectrum I'm
likely to find interference.
        Comments?

Thanks!

Harold