The Myths of LF vs. HF

Let's address these claims one at a time, after taking a look at a short video showing a demonstration involving eight passive LF RFID tags attached to a toy train passing 32 RFID antennas (www.youtube.com/watch?v=jWEh58IUXoY). For those skeptics who will now claim this is a perfect lab environment, let's view another video in which the products are on display at a trade show (www.youtube.com/watch?v=Wx27TkjEOUU&feature=related).

Read Speed. Each time the train does a loop, there is an occurrence of eight times 32 reads, and we have run this setup for days on end without missing a read—the U.S. Food and Drug Administration (FDA) demands such a high performance level in certain applications—so I would assume that is proof enough for readers. Although the speed is not documented, I challenge any HF company to match these speeds. Yes, HF has a higher bit-rate transmission rate from the tag. Why? Well, HF tags tend to have higher amounts of memory, and faster bit-rate transmissions are necessary. However most current automation projects employ a tag's unique identification (UID) number, and those tags featured in the video are of a mere 8 bytes. While LF tags generally (though not always) tend to have smaller amounts of memory, it's not about the data-bit transmission rate, but rather the reader's decoding (demodulation) speed and the communication process from the reader to a host. A third video (www.youtube.com/watch?v=0lhL2QB3a-U) shows the train completing a loop in just 7 seconds (256 reads), which equates to a read every 27 milliseconds.

Proximity of Readers and RF Interference. HF readers placed close to each other (5 inches apart) will interfere with one another, and a diminished or zero read range will result. There is no diminishment of performance in these LF systems, however. (Note: Not all LF systems are the same, and the intellectual property of those represented in the videos make the difference.)

Cross Talk. HF readers placed in such proximity to each other will result in cross talk—the reading of a second or third tag instead of the tag directly positioned to the interrogator. There is no cross talk with these LF systems.

Metal. While the video does not show metal, these products can be mounted on metal, and in highly metallic environments, without performance degradation. In fact, metal can help to strengthen read-range performance, due to the properties of RF reflection.

Read Ranges. LF actually exceeds HF in read-range performance. Just ask the folks in Charlotte, N.C., about their tests of HF vs. LF and read-range performance for the new NASCAR museum being put together. The LF system performed at 4 inches, versus 2 inches for the identical interrogator and tag size. There are LF tag and reader combinations that will read in excess of 1 meter (3.3 feet). Naturally, this takes an extremely large reader antenna (4 feet by 2 feet), and a tag nearly the size of a sheet of paper. I know of no HF systems that can perform as such, though there may very well be one or two I don't know about.