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  1. #1
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    nfc antenna

    Hi, I read in data from a card wirelessly using an RFID coil but when I introduce a magnetic field near the antenna coil, the data is corrupted. How would a filter be performed digitally to get rid of the low frequency magnetic field? The magnetic has to exist in close proximity to the RFID coil.

    Thanks

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  2. #2
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    nfc antenna design

    Hello,
    are you able to distinguish, if the intereference is at reader or at the card side? I think both could be. The reader antenna circuits I know, mainly Philips, have capacitive coupling and should not be succeptible for low frequency interferences. Or could it be, that the "low frequency" field has harmonics up to 13.56 MHz?

    Can you specify the LF field in terms of waveform and field strength?

    A RFID reader, could be NFC, Mifare, ISO14443, whatever is already a selective receiver and would not necessarily have much headroom for optimization. You should consider that it has to detect small load modulation in presence of strong reader field.

    At the card side, the coil is usually DC coupled to the IC. It utilizes a resonance circuit but does not particularly filter LF components. If interfering field induces sufficient voltage in the card coil, it could disturb both communication directions, I think. The bad thing would be that you can't cange this situation without modfying the card.

    Regards,
    Frank



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  3. #3
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    nfc antenna near field

    Hi Frank, the reader and card are fine when working on their own. The problem is due my introduction of a magnetic field near them as it is part of a single entity, i.e. I have to integrate the reader with the device generating the magnetic field, as such, when I bring the card near to be read by the NFC reader, the magnetic field interferes. The data that I read in from the card is different with and without the magnetic field.

    Therefore, I have to find some way of filtering the LF magnetic field without any hardware addition, and do some digital filtering. I would appreciate some advice or options! Thanks.

    Kelvin



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  4. #4
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    nfc anten

    Yes, I basically understand this from your first posting.

    I said, if the field would interfer card circuit operation, it may be hard to overcome. As you apparently have difficulties to indentify the interference mechanism in detail, I asked about LF field parameters to judge from my knowledge of RFID operation, if the card is likely to be succeptible under this conditions.

    I also said, that I doubt if usual card readers could be improved much regarding interference suppression, knowing that the antenna circuit would normally filter LF interference. That may different with some reader designs. It is necessary anyway to know the utilized reader IC and the reader antenna design.

    P.S: Filtering the LF field itself sounds promising and should be done also to understand the interference mechanism in detail.



  5. #5
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    13.56mhz antenna harmonic suppression

    Hi Frank

    Sorry for replying too fast without fully comprehending your reply. The NFC reader I am using is PN531, from your experience, it should be picking the LF, rather it is more due to the LF being coupled to the card when brought near, thereby, causing the interference. I will try measuring the magnetic field if possible. Thanks.



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