Concept
LF, HF, UHF
Three slices of the radio spectrum, three completely different kinds of RFID.
RFID isn't one technology. It's three families that happen to share a name, split by the frequency they use:
| Band | Frequency | Read range | You know it as |
|---|---|---|---|
| LF | 125 / 134.2 kHz | a few cm | office prox badges, pet microchips |
| HF | 13.56 MHz | a few cm (up to ~1 m) | NFC, payment cards, transit, hotel keys |
| UHF | 860–960 MHz | metres | retail tags, race bibs, warehouses |
Slide through the spectrum and watch what changes:
#Why the band matters so much
- Antenna size. Antennas want to be a decent fraction of a wavelength — or, at low frequencies where that's impossible, a coil with many turns.
- Range. LF and HF tags couple to the reader through a magnetic field that falls off very fast. UHF tags catch an actual radio wave from metres away.
- Speed. Higher frequency, more cycles per second, more room for data.
- Water and metal. LF shrugs them off (that's why pet chips are LF). UHF struggles near both.
#Same job, three antennas
Pull the plastic off a tag from each band and the frequency is written all over the antenna:
A reader for one band can't talk to tags in another — your phone can't read a 125 kHz badge no matter what app you install.