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FourQ View Drop Down
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Joined: 19 June 2009
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FourQ Quote  Post ReplyReply Direct Link To This Post Topic: Ghost tags
    Posted: 26 June 2010 at 4:10pm
I don't know which part of the boards to place this so I figured this would be a good a place as any.

Periodically I'm picking up phantom tags.  Nobody's at the reader and the chances of tags levitating is sufficiently slim for me to rule it out.

I've been racking my brain to come up with an explanation but thus far the only thing that has come to mind is someone's central locking system working on 125KHz.  I'm just wondering if anyone else has had tags showing on their logs in such a manner?

I'm also concerned as I have friends whose bike alarms/immobilisers or car locking systems may work on 125Khz.
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amal View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amal Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2012 at 11:07am
Hey FourQ, sorry for missing this whole security section of the forum... I forgot to "watch" this entire section and missed a ton of posts from people.

Even though it may not be relevant anymore, I've seen these kinds of phantom reads on cheap readers that do not bother with calculating parity and verifying they are actually receiving signals from an actual tag.

Magnetically coupled passive readers generate their own resonant field, then "listen" for power drains and power spikes in that field. Tags communicate by modulating the amplitude of the field "wave", not the frequency of it, so a reader picking up even the slightest interference may mistake those changes in power levels for a tag trying to communicate. The parity calculation is supposed to rule out false data, however it requires that the reader actually perform said calculation and validation before spitting out the data.
Amal ;)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote FourQ Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2012 at 11:16am
I'd forgotten about this post myself.  It turns out it was car alarms/immobilisers causing false reads. This was confirmed by a controlled test with a BMW and the Parallax reader.

The middleware is supposed to resolve parity discrepancies.

Thanks for replying.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amal Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2012 at 11:38am
Cool man :)
Amal ;)

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