Hello everybody !
I have an arduino Mega 2560 and an antenna like this http://pykt.it/yTsK (we don't care about the little module)
My question is :
Can I (and if I can, how) dump a raw RFID signal between a card and its reader/writer ?
I spent a lot of time on Google but I did not find anything 
Thank you very much ! 
(Sorry if I don't write English well, I'm French)
What do you mean by dump the raw signal?
What sor of RFID are we talking about?
With a smart card running at 13MHz there is not much you can do with a 16MHz processor.
With a 125KHz card you will need to be able to take samples at about 1MHz which is again too fast for a low speed processor like the arduino.
Why do you want to do this? There must be a better way of acheaving what you want.
It is a 13MHz smart card so I think I can't do anything 
When I say Dump the raw signal, I want to dump the modulated signal what is sent by the writer, in order to send it with a simple other antenna without any decoding.
On a 13MHz card the card talks back to the reader at 3.25MHz so it is still not possible.
Okay, thank you very much !