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[aprssig] RFID bigger coil

Robert Bruninga bruninga at usna.edu
Thu Feb 25 17:26:58 UTC 2010

Biggest RFID Coil yet.

Today,  I doubled the size again to a 23" square coil and it
works well.  Resonance was not as peaked, but its vertical
detection range was
still about 12" and the outside-the-coil range was about 5"
giving an overall
HotSpot of nearly 33" across.  THe advantage of this larger coil
is that a moving
tag is in the coil longer and therefore can be detected at a
faster speed.
Even throwing a card across the coil Frysbee style would always

Shucks, in two more doublings of the size, it will be big enough
(3' by 7') that might surround a door!  I cannot imagine that it
could possibly work because the field will be so weak... But who


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