Re: [Discuss-gnuradio] RFID receiver

[Harald Welte]

On Tue, Oct 24, 2006 at 09:49:41AM +0200, Erlend Barstad Strand wrote:

> I have changed the focus of my pre-project sligthly, so I will not try
> to make an RFID receiver this semester, I might try next though.

what a pity.
 
> If I do try this next semester, it will be a RFID receiver of the ISO
> 14443-2 standard. The aim of the project will simply be to sniff on the
> communication between a card an a reader. The reason for chosing ISO
> 14443-2 is simply that I have a RFID reader available using this
> standard.....

ISO 14443-2 Type A or B ?

In any case, the problem is the dynamic range.  Even with those
magnetically coupled systems, the field emitted by the reader is at
least 60dB stronger than the load modulation (subcarrier) that you get
back from the transponder/card.

This problem is further complicated by the fact that the reader-carrier
and the lower sideband of the transponder-subcarrier are (depending on
bit rate) 400kHz apart in the spectrum


Therefore you definitely need some very steep filter to separate the
modulated subcarrier signal from the 

The OpenPCD project has developed a device for this job, which can be
used as a gnuradio frontend: http://www.openpcd.org/rfiddump.0.html

It is basically mixing the signal with a signal from a crystal oscillator
in order to get the signal down to 10.7MHz where you can use a stock
250kHz bandwidth ceramic filter for 10.7MHz to attenuate the reader
carrier.

This might be a good starting point...

We're currently working on dedicated (free) hardware for simulating a
14443 (A and B) transponder/smartcard, so we don't have time to put into
the sniffing project at the moment.

-- 
- Harald Welte <address@hidden>                         http://gnumonks.org/
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