MadSci Network: Engineering

Re: How does a passive RF sensor work? Is that what 'Easy Pass' tolls use?

Area: Engineering
Posted By: Gus Calabrese aka puppet boy, Design Engineer
Date: Fri Feb 21 11:13:59 1997
Message ID: 856527373.Eg

Passive RF can come in a number of forms.  One of the early methods 
was to excite a module with RF energy and measure the frequencies at 
which the module resonated.  Most recently modules derive their energy 
from RF energy aimed at them and they return a digital signal that 
is either active or based on switching the load the module presents 
to the transmitter.  I do not know what method is used 
with "Easy Pass" tolls.

Gus Calabrese

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