I am attempting to capture the radiated wave from a couple passive RFID tags, one which transmits at 125 kHz and the other at 134 kHz. I need to make a rudimentary AM antenna to detect these signals and view the modulation on an oscilloscope. I am currently using a signal generator and near field antenna probe to transmit a carrier to stimulate, bias, etc. the tag which takes the signal, modulates it, and re-transmits it. I need to capture this re-transmitted modulated signal and view it on a scope so I can decode the modulation. Any help would be greatly appreciated.

 

Are you serious about the frequency? It seems way to low to be practical. I say that because an efficient antenna at those frequencies is incredibly long and there is very little bandwidth for data transmission at those frequencies. Very slow CW on a waterfall display is about all you can manage.

 

A plain old ferrite loopstick should work.

I used to pick up LORAN transmissions at 100 kHz when working on circuits at my house. Even though the LORAN transmitters were several hundred miles away, it still was sometimes a struggle to keep the LORAN signal out of my breadboarded circuits. A few inches of wire at the input of an op-amp would pick up enough 100 kHz energy to show up on my scope.

 

There is quite a difference between a LORAN transmitter and a wimpy little RFID tag with passive components and no power supply. I'm actually doubting that a practical RFID tag can be built that will work at those frequencies.

Check out the following article that I came across.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en011766

Might take a while to work through that one though.

 

Here's a link to a Texas Instruments pdf that describes a 134.2 kHz RFID reader that uses a ferrite stick antenna.

http://www.ti.com/lit/an/swra284/swra284.pdf

 

Still no info on the available bandwidth utilized and how the messages are encoded and decoded.

 

Still no info on the available bandwidth utilized and how the messages are encoded and decoded.

Maybe the scope does not need it to show the signal... I guess.

 

There's a ferrite stick antenna in a cheap AM/FM radio I have at home. Would this be able to pick up the transmitted RFID signal? Would I need to remove some of the loops to tune it to the 134 kHz range?

 

Hello,

A ferrite antenna for AM (MW) can be tuned for 550 kHz to 1600 kHz.
http://en.wikipedia.org/wiki/Medium_wave
http://en.wikipedia.org/wiki/AM_broadcasting
A ferrite antenna for AM (LW) can be tuned for 150 kHz to 300 kHz.
http://en.wikipedia.org/wiki/Longwave

Bertus