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I'm trying to create a simple NFC/RFID software simulator and am having a hard time understanding the math fully. I know that NFC tags respond by load modulating the 13.56 MHz wave that the reader is sending it. I'm pretty sure NFC tags use a subcarrier wave with a frequency of ~847 kHz. Where I'm getting confused is how to model the result of the load modulation.

Can I simply take the 13.56 MHz wave and do a point-wise multiplication with the 847 kHz wave? Using the Manchester Encoder, this nets me a signal that looks like this: Image

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After measuring a NFC tag with a USRP and making a couple of simulations in octave and python, it seems like I was incorrect regarding the point-wise multiplication. As it stands, I believe the best simulation is to do an addition of the carrier wave (13.56 MHz) and the subcarrier wave (847 kHz), with the subcarrier wave's amplitude set at 0.1x the amplitude of the carrier wave.

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