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#1 2013-04-27 08:01:53

asper
Contributor
Registered: 2008-08-24
Posts: 1,409

How to build a NON-125kHz or 13.56MHz antenna

Hi guys, here is my question;

if I have a tag that is working at a custom frequency (probably 3 or 6 MHz) but I am pretty sure that the communication protocol is the same as another 125kHz product, will I be able to use an already implemented 125kHz command (ex. "lf read") changing only the coupling antenna or should I have to write a new code in PM3 ?

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#2 2013-04-27 15:14:25

vivat
Contributor
Registered: 2010-10-26
Posts: 332

Re: How to build a NON-125kHz or 13.56MHz antenna

For LF carriers you can change the divisor using function(armsrc)
FpgaSendCommand(FPGA_CMD_SET_DIVISOR, XXX);
where XXX is divisor number.
You can use following formula to calculate carrier frequency
12Mhz/(divisor+1)
For example you want to set it to 125 khz:
12Mhz/(95+1)
This is similar to
FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95);
Another LF example:
FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 88); //134.8Khz
You can set it up to 600 khz.

For HF you probadly can change carrier frequency by modifying FPGA code i.e. dividing ck_1356meg signal in the way like generating a subcarrier from external reader's clock.
13.56/2=6.78
13.56/4=3.39

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#3 2013-04-27 16:05:01

asper
Contributor
Registered: 2008-08-24
Posts: 1,409

Re: How to build a NON-125kHz or 13.56MHz antenna

Thank you for your quick answer vivat! Do you think Is it possible to implement this kind of hf function for 4150 lf protocol tags?

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#4 2013-04-28 09:54:36

vivat
Contributor
Registered: 2010-10-26
Posts: 332

Re: How to build a NON-125kHz or 13.56MHz antenna

Can you give more details?

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#5 2013-04-28 10:12:47

asper
Contributor
Registered: 2008-08-24
Posts: 1,409

Re: How to build a NON-125kHz or 13.56MHz antenna

I have a tag that probably is 3 or 6 MHz made by EM Microelectronics but I am pretty sure that it uses a communication format simil if not identical to lf EM41x0 tags so I would like to read it using PM3 already implemented commands and my HF antenna... will it be possible ?

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#6 2013-04-29 13:49:54

vivat
Contributor
Registered: 2010-10-26
Posts: 332

Re: How to build a NON-125kHz or 13.56MHz antenna

No, I don't think so because as you said in your post, the carrier frequency is 3 or 6 MHz. Proxmark can generate 13.56 mhz carrier, try to divide it by 2( or 4). IMHO Without touching the code and making better antenna it is impossible.

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