Interrogator

Interrogator

An RFID reader device." data-category="General">interrogator is the device in an RFID system that initiates communication by transmitting RF energy and commands, then receives and decodes responses from transponders (tags). In everyday usage, "interrogator" and "RFID reader" are synonymous. The term comes from radar terminology, where an interrogator sends a challenge signal and awaits a reply.

Reader Form Factors

How an Interrogator Works

1. Transmit -- the reader generates a continuous-wave RF carrier at the designated frequency (e.g., 902-928 MHz in the US) and modulates it with commands defined by the EPC Gen2 protocol.
2. Singulation -- the reader uses anti-collision algorithms (the Q-algorithm) to isolate individual tags from the population.
3. Receive -- the reader's sensitive receiver detects the tag's backscatter modulation (FM0 or Miller encoding).
4. Decode and filter -- baseband processing extracts the EPC and optional sensor or user memory data.
5. Report -- tag reads are sent to host software via LLRP, MQTT, or proprietary APIs.

Regulatory Constraints

Reader transmit power is limited by regional regulations. In the US, FCC Part 15 allows up to 1 W conducted power (36 dBm EIRP) with FHSS across 50+ channels. In Europe, ETSI limits power to 2 W ERP at 865-868 MHz with Listen Before Talk channel access. These differences affect both read range and reader deployment density.

See also: Portal Reader | LLRP | Readers