Also known as: NFC RF, NFC air interface, NFC physical layer
NFC (RF layer) is the short-range physical interface behind contactless cards and tap-to-pay, operating at 13.56 MHz through inductive coupling rather than a radiating wave.1 A reader’s coil and a tag’s coil act like a loosely coupled transformer in the antenna’s near field: the reader supplies energy and a clock, and the tag replies by modulating the load it presents. This page covers the radio interface; for the everyday concept see near-field communication.
Overview
NFC is high-frequency (HF) RFID with an added peer-to-peer mode. The reader drives an unmodulated (or ASK-modulated) 13.56 MHz carrier through its coil. A nearby passive tag rectifies that field to power its chip, and to answer it switches an extra load on its own coil on and off. That switching reflects back as tiny amplitude changes on the reader’s carrier — often carried on a subcarrier offset (typically 847 kHz) — which the reader detects. Because coupling falls off very steeply with distance, range is only a few centimetres; short range is a security feature, making a tap deliberate and hard to intercept from afar. The reader sends data by amplitude-shift keying the field.
Technical characteristics
| Property | Value |
|---|---|
| Frequency | 13.56 MHz (HF ISM) |
| Coupling | Magnetic (inductive) near field |
| Range | ~1–4 cm |
| Reader → tag | ASK (100% or 10%) |
| Tag → reader | Load modulation on ~847 kHz subcarrier |
| Data rate | 106 / 212 / 424 kbit/s (typical) |
| Base standards | ISO/IEC 14443, 15693, 18092 |
Modes include card emulation (a phone acting as a contactless card), reader/writer (a phone scanning a tag), and peer-to-peer. The relevant standards — ISO/IEC 14443 for proximity cards and 18092 for NFCIP — define framing and bit rates on top of this radio.
History
NFC grew out of HF RFID work by Sony (FeliCa) and NXP (Mifare), formalised around 2003–2004 and promoted by the NFC Forum. Its breakout came with smartphone wallets and transit systems in the 2010s.
Deployment
NFC is everywhere contactless: payment cards and phone wallets, transit fare cards, access badges, and product tags. It complements longer-range radios in a phone, handling the intentional “touch here” interactions rather than networked data.
Decoding it with GopherTrunk
GopherTrunk does not decode NFC. Its 13.56 MHz inductive, near-field interface is a fundamentally different regime from the far-field VHF/UHF signals GopherTrunk targets, and it is not radiated in the usual sense — you cannot receive it at range with an ordinary antenna. NFC analysis uses dedicated readers or purpose-built HF probes, well outside GopherTrunk’s land-mobile and aeronautical scope.
Sources
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Near-field communication — Wikipedia, on the NFC air interface, 13.56 MHz inductive coupling, load modulation, and the ISO/IEC standards; see also ISO/IEC 14443 for the proximity-card layer. ↩