FDX and HDX are two communication methods used in low-frequency RFID animal identification. In this context, FDX usually means FDX-B, the standardized full-duplex format used alongside HDX under ISO 11784/11785.
Both can identify livestock and other animals, but they communicate with the reader differently. That difference affects reader compatibility, noise tolerance, and read performance.
What Is FDX-B?
FDX-B stands for Full Duplex B. It is the FDX format used in the ISO animal identification system.
An FDX-B reader generates a 134.2 kHz magnetic field that powers the passive transponder. The tag sends its data back while that field remains active, so the tag receives energy and returns its identification signal during the same part of the read cycle.
“Full duplex” can sound as if the reader and tag are having a conventional two-way conversation. In animal RFID, it specifically describes the tag transmitting while the reader continues supplying the activation field.
FDX-B uses load modulation with amplitude-shift keying (ASK). The transponder changes the electrical load on its coil, producing variations in the reader’s field that the receiver can detect. The tag changes the electrical load on its antenna coil, creating changes that the reader can detect in its field. The complete FDX-B telegram is 128 bits, including the animal identification information and the additional bits required for transmission and error checking. The 128-bit figure describes the transmitted frame, not the amount of writable user memory in the tag.
The ISO standards divide two related jobs. ISO 11784:2024 defines the structure of the animal identification code, while ISO 11785:2026 defines how the transponder is activated and how its information is transferred to the reader.
How Is FDX-B Different From FDX-A?
FDX-A refers to older, non-ISO full-duplex animal-identification formats, typically operating around 125 kHz. Unlike FDX-B, it is not the standardized full-duplex protocol specified by ISO 11785. FDX-A is mainly encountered in legacy animal-identification systems and is not compatible with ISO FDX-B merely because both are low-frequency technologies.
FDX vs HDX: Key Differences
FDX-B and HDX can carry the standardized animal identification code, but the way that code reaches the reader is different.
| Jellemző | FDX-B | HDX |
| Communication timing | Tag responds while the reader field remains active | Tag responds after the reader field is switched off |
| Tag power during response | Continues receiving energy from the reader field | Uses energy stored during the activation period |
| Response method | Amplitude-based load modulation | Frequency-shift keying (FSK) |
| Telegram length | 128 bits | 112 bits |
| Electrical noise behavior | More sensitive to some amplitude noise | Generally stronger immunity to amplitude noise |
| Reader requirement | Reader must support FDX-B | Reader must support HDX |
The noise difference can matter in livestock installations. Motors, electrical equipment, and large metal structures can create a difficult electromagnetic environment around a race, crush, or automated handling system.
HDX has an advantage in many of these installations because the reader stops transmitting before it receives the tag response. Its FSK signal is also less vulnerable to amplitude noise. Livestock equipment suppliers therefore often use HDX where longer or more consistent reads are required in electrically noisy cattle-handling areas.
However, that advantage does not make HDX universally better. FDX-B remains widely used in standardized animal identification, including electronic ear tags and injectable transponders. The ICAR registry contains current compliant devices using both FDX-B and HDX.
FDX vs HDX Read Range
HDX can provide a longer or more consistent read range than FDX-B in some comparable LF systems, particularly in environments where receiver noise or the reader’s own carrier limits FDX-B reception. There is no fixed distance that separates the two technologies.
Read range depends heavily on the transponder antenna and the reader antenna. Tag orientation also changes the magnetic coupling between them. Reader power and background electrical noise further affect how far away the tag can be detected.
A large cattle ear tag therefore cannot be compared directly with a small injectable transponder simply because both use FDX-B or HDX. A larger tag coil can capture more energy from the reader field and generally supports a greater practical read distance.
HDX gains another advantage during reception because the reader’s strong activation carrier is no longer present when the tag responds. The receiver can listen for the weaker tag signal without separating it from its own continuous carrier.
Can the Same Animal RFID Reader Read FDX and HDX Tags?
Yes. A reader can support both FDX-B and HDX, but it must be designed for both protocols.
Operating at 134.2 kHz alone does not guarantee compatibility. The reader has to handle two different communication cycles. It can detect FDX-B while its activation field is running, then switch the field off at the required intervals so it can listen for an HDX response.
This dual-protocol support is especially useful where animals carrying different ISO-compatible tags pass through the same identification system. The reader can retrieve the standardized ID from either tag type without requiring separate scanning equipment.
Gyakran ismételt kérdések
Q1: Is FDX the Same as FDX-B?
In livestock and animal RFID, FDX is commonly used as shorthand for FDX-B.
FDX-B is the precise term for the full-duplex format used under ISO 11784/11785. FDX-A is a separate older 125 kHz technology.
Q2: Are FDX-B and HDX Both 134.2 kHz?
Both are part of the ISO animal identification system built around a 134.2 kHz reader activation field.
Their tag responses are different. FDX-B returns data while that field remains active, while HDX waits for the reader field to switch off and then returns its FSK signal.
Q3: Can a 134.2 kHz RFID Reader Always Read Both FDX-B and HDX?
No. A 134.2 kHz reader may support FDX-B, HDX, or both.
The frequency tells you where the system operates. Protocol support tells you which transponders the reader can actually decode. Always check the reader specification for explicit FDX-B and HDX support.
Q4: Can FDX-B and HDX Tags Be Used in the Same Herd?
Yes. Animals with FDX-B and HDX tags can be managed in the same herd if the readers used at scanning points support both protocols.
The animal management software also needs to accept the identification data coming from the reader, but the standardized animal ID structure allows both tag technologies to participate in the same identification system.
Q5: What Is the Difference Between 100 Mbps FDX and HDX?
In a 100 Mbps Ethernet connection, FDX and HDX describe network duplex mode and have nothing to do with animal RFID.
100 Mbps FDX allows the Ethernet interface to transmit at up to 100 Mbps and receive at up to 100 Mbps at the same time. 100 Mbps HDX still has a 100 Mbps link rate, but sending and receiving share the medium and cannot happen simultaneously.
Full duplex is standard on modern switched Ethernet networks. Half duplex is mainly associated with older shared-media equipment such as hubs.
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