Josh Koffman wrote:
> There definately is such a thing. I don't know anything about it, but
> look for information on how the automatic transponders for toll roads
> work. My guess is a higher power energizing beam, and a directional
> antenna.

The ones here houston use a battery powered transmitter that responds to
the toll booth signal.  From what I've read recently about RFID tags
(the low frequency ones), there is no way anyone will read them from
200mtrs at 60kmh.  Just to read them from 1-2mtrs requires a huge loop
antenna with over 1000 volts applied to the terminals in order to induce
enough juice into the RFID tag so that it can power up, and that's good
for only 2mtrs.  I wonder just how big of a loop and how much voltage
would be required to power it up at 200mtrs.

michael

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