Also known as: Bluetooth Classic PHY, BR/EDR, Bluetooth radio
Bluetooth (RF layer) is the short-range radio physical layer that carries Bluetooth personal-area links over the 2.4 GHz ISM band using frequency-hopping spread spectrum and GFSK modulation.1 Standardised by the Bluetooth SIG, it hops rapidly across the band to dodge interference and eavesdroppers; the everyday concept is covered at Bluetooth.
Overview
Bluetooth Classic (BR/EDR) divides the 2.402–2.480 GHz band into 79 channels spaced 1 MHz apart and hops between them 1600 times per second in a pseudo-random sequence shared by the connected devices, or piconet. Each 625 µs slot carries a packet on a new frequency, so narrowband interferers only spoil the occasional hop. Adaptive frequency hopping (AFH) further improves coexistence by skipping channels known to be busy with Wi-Fi. The basic rate uses GFSK at 1 Mbit/s; Enhanced Data Rate (EDR) switches the packet payload to π/4-DQPSK (2 Mbit/s) or 8DPSK (3 Mbit/s).
Technical characteristics
| Property | Value |
|---|---|
| Band | 2.402–2.480 GHz ISM |
| Channels | 79 × 1 MHz (Classic) |
| Hop rate | 1600 hops/s |
| Modulation | GFSK (BR); π/4-DQPSK, 8DPSK (EDR) |
| Symbol rate | 1 Msym/s |
| Bit rate | 1 / 2 / 3 Mbit/s |
| Coexistence | Adaptive frequency hopping |
The spread-spectrum design trades peak throughput for resilience in the shared ISM band. A companion low-power variant, Bluetooth LE, uses a different, simpler channel plan aimed at battery devices.
History
Ericsson began the work in 1994; the Bluetooth SIG published version 1.0 in 1999. EDR arrived with version 2.0 (2004), and Bluetooth 4.0 (2010) introduced the separate Low Energy layer. The name and the runic logo reference the 10th-century Danish king Harald “Bluetooth” Gormsson.
Deployment
Bluetooth Classic dominates wireless audio (headsets, speakers, car kits) and legacy peripherals. Newer sensor, wearable, and IoT devices increasingly favour the LE variant for its lower power draw.
Decoding it with GopherTrunk
GopherTrunk does not decode Bluetooth. Following a frequency-hopping link requires tracking 1600 pseudo-random hops per second across 80 MHz of spectrum with knowledge of the piconet’s hop sequence and clock — a very different problem from GopherTrunk’s fixed-channel land-mobile decoders. To GopherTrunk, Bluetooth is simply another occupant of the noisy 2.4 GHz band that an SDR operator learns to recognise.