[aprssig] RFID bigger coil

Wes Johnston, AI4PX wes at ai4px.com
Thu Feb 25 12:35:47 CST 2010

Why not rectangular, say 4" x 30" to cover the threshold of a door?


On Thu, Feb 25, 2010 at 12:26, Robert Bruninga <bruninga at usna.edu> wrote:

> Biggest RFID Coil yet.
> Today,  I doubled the size again to a 23" square coil and it
> also
> 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
> detect.
> 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
> knows..
> Bob, WB4APR
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God help those who do not help themselves.
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