Member Since: February 6, 2009

Country: United States

  • I agree that the RFI card you are showing is most likely a 125khz card. A 13.5 Mhz card has only one or two windings.
    Here’s the thing. When you fold the coil to fit into the key, you change it’s inductivity as you increase the number of coil windings (by folding it). Inside the chip is a fixed value capacitor which forms a resonant circuit with the coil. The resonant frequency of this circuit determines the operating frequency of the card. If you folded the coil you have increased it’s inductivity. thereby lowering it’s resonance frequency. You could counteract this by reducing the number of coil windings (or, better, wind a completely new coil). If you want to be completely sure of the operating frequency of it’s base station, wind 3 feet of wire into a coil and attach it to an oscilloscope (or a counter) and watch the waveform.

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