Gen 2 (915 MHz) has read ranges measured in meters, while HF (13.56 MHz) range is measured in cm. Check out "How to Build a Low-Cost, Extended Range RFID Skimmer" for how to increase read range for HF devices; they got about 35 cm. But to answer your question, I just use a vanilla circular antenna which is pretty standard for Gen 2 applications.
Michael > Hello All, > I'm trying to do more or less the same thing as Kevin but with two other > readers (a RFIdeas Playback and an OpenPCD) and other kind of cards (HID > IClass 2K and Mifare Classic 1K: both working at 13.56MHz). > I got an interesting signal just putting my loop antenna attached both > to the card and the reader: even if it is a bit weak, I can recognize > the tag reply. > (USRP 1, BaseRX with the usrp_rx_cfile.py -f 13560833 -r B -d 16) > One of the problems I have is that I have to stay as much close as I can > to the card to be able to read its response (from more than 3 inches I > get an unreadable signal...), so I would like to ask Michael which kind > of antenna (and any external things) you used to be able to read the > signal from few feet away. Any suggestions will be very well appreciated. > Thank you very much, > Marco > > Michael Buettner wrote: > > Are you using the ThingMagic in monostatic mode (one antenna that does RX > > and > > TX)? If so, you probably won't be able to see the tag reply. Further down > > the > > receive path the ThingMagic has circuitry that removes the strong TX signal > > leaving only the tag reply, but I assume you are tapped in before that. You > > MIGHT have better luck if you use the reader in bistatic mode and tap in at > > the > > receive antenna, particularly if you don't use the full 1W output power. > > Another > > option would be to just put the USRP antenna near the tag, and receive both > > reader and tag commands there. I have had pretty good luck with that, and > > can > > decode tag responses from a few feet away. > > > > > > michael
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