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How Important Is the Data-Modulation System That a Particular Tag Uses, in Terms of Reader Compatibility?

Posted By RFID Journal, 02.14.2013
I am employing custom-made stationary RFID readers in a field experiment, but I'd also like to be able to utilize a handheld unit in certain circumstances. The tags I am using are 125 kHz ASK tags. I wish to know if a handheld described as reading all FDX-A and FDX-B tags would be able to interrogate my ASK tags. Thank you.

—Name withheld

Modulation is very important. To answer your question about whether a handheld designed to read both types of FDX (full duplex) tags—which utilize amplitude shift keying (ASK), a method of communicating stored data by changing the amplitude of the waves sent back to the reader—I reached out to James E. Heurich, the president of RFID, Inc., one of the few companies still producing low-frequency (LF) RFID systems. Here is James's response:

"Modulation is one of the key characteristics in making a system proprietary. Obviously, a tag using ASK cannot be read by a reader looking to demodulate in Manchester, Bi-Phase, or phase shift keying (PSK). It is only the first line of defense, so to speak, when encoding and decoding proprietary tags. But just because you have an ASK-encoded tag and an ASK reader doesn't mean they will work together. There are a myriad of further methods to make a tag proprietary, such as the number of bits used per byte, the divide-by rate, a custom CRC algorithm, and secret header bits which alert the reader that a valid bit string follows. When you describe FDX-A and FDX-B, it normally means the animal industry around ISO 11784/5 at 134.2 kHz, which is usually interchangeable between vendors. At 125 kHz, you tend to find hardware in the ASK FDX-A/B realm that is both proprietary and open; it depends upon the vendor. If I knew who the vendors in question were, I could advise whether or not the tags could be read by the reader. For now, unfortunately, there's only one way to find out: test."

—Mark Roberti, Founder and Editor,
RFID Journal

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