Is there a way of knowing which tag operates at which particular frequency?
That’s an interesting question—and one that no one has asked me before. I’ll offer my opinion, and I hope that other RFID experts will suggest other, better ideas as well.
Most passive low-frequency (LF) tags operate at 124 KHz or 134 KHz. LF tags are distinguishable by their antenna, as they have a thin copper wire that is coiled many times (see image below). It is difficult to detect, from just looking at the tag, whether it is operating at 124 KHz or 134 KHz. If the manufacturer’s name or a model number is printed on the tag, you will probably be able to search the Internet to find its specifications. Or you might be able to call the manufacturer to determine the frequency and protocol used.
High-frequency (HF) tags operate at 13.56 MHz, and are easily distinguishable by their coiled antenna. HF tags typically have a thicker copper antenna that doesn’t loop as many times as the LF tag’s antenna (see image below).
Passive ultrahigh-frequency (UHF) tags have a wide variety of antenna shapes and sizes, but usually do not have loops (near-field UHF tags do have a loop). UHF tags operate between 860 and 960 MHz. It is impossible to tell the precise frequency of a UHF tag just by looking at it. Again, the best way is to determine if there is a manufacturer or model number on the tag, and then search the Internet for specifications. Some examples of UHF tags are shown below.
Active tags can operate at 433 MHz, 915 MHz, 2.45 GHz, 5 GHz and other frequencies. There is no way of knowing which active tag operates at which frequency without looking up the specific make and model number, or contacting the manufacturer.
—Mark Roberti, Founder and Editor, RFID Journal