Hi Everyone,

I'm working to build an RFID reader for animal tags, and I have a quick question related to this project.

The ISO11784/11785 standard leaves a good deal of room in tag design. However, it seems like almost universally small animal tags are full-duplex and ASK. My question is how do I separate the modulated signal from the carrier signal? There's plenty of information on simply demodulating an ASK signal, but not accounting for the carrier signal as well.

Thanks in advanced for the help.

Austin

 

I don't think you understand how ASK works.

 

Can you elaborate?..I think I might have an idea of what you're referring to.

In reading over the wiki on the ISO standards they say that ASK is used for full-duplex and FSK is used for half-duplex. I don't think this would make sense, since there isn't a reasonable way to demodulate when the amplitude shifted signal is overlaying the carrier frequency. It would make more sense if ASK were used for half-duplex and FSK for full duplex.

 

hi ski,
The high carrier frequency is amplitude modulated with a lower frequency, usually the data, in order to create an ASK modulated signal.

A simple diode and R/C circuit can be used to rectify the modulated carrier in order to recover the original modulating data signal, the carrier frequency amplitude on the demodulated signal is very small and can be easily removed with a low pass filter.

Full duplex means that the remote TX/RX and local TX/RX can transmit and receive data from each other at the same time, simultaneously.

Half duplex means only the remote or local transmitter can be sending at any on time, not simultaneously .

E

 

Full duplex means that device (whatever the device might be) can transmit and receive at the same time. Usually this means that the device (whatever the device might be) has two circuits: one circuit to transmit, one circuit to receive. The type/nature of the signal DOES NOT MATTER.

From looking at wiki: If you have some kind of signal (wave), you have 1. If you have no signal (no wave), you have ZERO. That is ASK at it simplest. So if you have carrier, you have 1; if you don't have carrier, you have ZERO. If you remove carrier, then all you have is ZERO. So if you transmit 1101 and you receive with your demodulator 0000, then you failed.

 

Ok. Thanks for the replies. That makes a lot more sense. I was under the impression that any amplitude modification happened at the carrier frequency, which would most likely make demodulation near impossible.