I want to build a magstripe spoofer as a weekend project. I've seen others online do it using a steel shim wrapped in wire. This is only one coil. What can't understand is if cards have multiple tracks, how can one coil emulate all three tracks being swiped through. I thought I would need at least three thin steel strips each connected to a separate coil to spoof the 3 tracks found on a magstripe.
Are they somehow spoofing all three tracks through the one coil, or are they only building single track spoofers?
EDIT: Example of one http://hackaday.com/2008/08/04/magnetic-stripe-card-spoofer/