On Sun, Sep 07, 2008 at 10:16:04AM -0400, Philip M. Lanese wrote: > ChoJin, > > Commercial 13.56 MHz RFID systems don't normally use a receiver in the > traditional sense to recover the tag data. > > RFID manufacturers catering to the retail industry consider Tag Readers to be > a > necessary give-away that allows them to sell millions of tags, so cost is > always > driven towards the cheap end. > > The tag operates in the magnetic field close to the reader transmitter antenna > and switches its antenna in and out of "resonance" at 13.56 MHz with the > logic 1 > / logic 0 data stream output by the tag after an internal capacitor is charged > by the 13.56 RF energy and powers the internal logic circuits on, thereby > causing the reader antenna to hopefully have lower / higher Return Loss > corresponding to the tag digital data stream. > > Think of using an o'scope to measure the voltage across a resistor that is in > series with the primary winding of a transformer while you open and short the > secondary winding. > > Commercial systems measure the rectified output of a return loss measurement > circuit in series with the reader antenna to sense the data stream from the > tag. > Most of the work is put into the design of the reader antenna, which is very > small in terms of wavelength, to increase the difference in the amplitude of > the > millivolt level of the R/L output produced by the very small tag antenna > being > "in" and "out" of resonance. > > Phil, K3IB
Here's a link to the "Open RFID reader": http://www.openpcd.org/ See also http://www.openpcd.org/rfiddump.0.html It's been used with GNU Radio... Eric _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
