---
title: "Spread spectrum frequency hopping in Bluetooth"
subject: "Instrumentation II"
chapter: 5
key: "semester_5/instrumentation_ii:freq-hopping-bt"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/freq-hopping-bt
site: BCT Engineering
---

# Spread spectrum frequency hopping in Bluetooth

Instrumentation II · Chapter 5: Data Acquisition And Transmission

- Asked in: 2073 Shrawan, 1+2 marks; 2072 Chaitra, 2 marks (asked 2 times)
- Video: [How Bluetooth Uses 79 Channels to Avoid Interference.  (Frequency Hopping Spread Spectrum Explained)](https://www.youtube.com/watch?v=7eoEKPK3rVY) — Technologies Discussion
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/freq-hopping-bt
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-5

## Question

What is spread spectrum frequency hopping in Bluetooth? Write the application of Bluetooth.

## Short answer

Bluetooth uses frequency hopping spread spectrum across 79 channels, changing 1600 times per second based on the master’s address and clock, with adaptive hopping to avoid interference. Applications include wireless audio, data transfer, peripherals, sensor networks, and medical devices.

## Answer

#### Frequency hopping spread spectrum (FHSS) in Bluetooth
**Spread spectrum** spreads a narrow-band signal over a much wider band to resist interference and interception. In **frequency hopping**, the carrier frequency changes rapidly in a pseudo-random sequence known to both transmitter and receiver.

In Bluetooth:
- The 2.4 GHz ISM band (2402-2480 MHz) is divided into **79 channels of 1 MHz**.
- The radio hops **1600 times per second** (a new channel every 625 us slot).
- The hop sequence is derived from the master's device address and clock, so all slaves of a piconet follow the same pattern.
- Adaptive frequency hopping (AFH) avoids channels with interference (for example Wi-Fi).
- Benefits: resistance to interference and fading, security, and coexistence of many piconets.

#### Applications of Bluetooth
1. Wireless headsets and speakers; hands-free car kits.
2. Data transfer between mobile phones, laptops and PCs; file sharing.
3. Wireless keyboards, mice, game controllers and printers.
4. Wireless sensor networks and data loggers.
5. Medical and fitness devices, smart-home devices, beacons and location services (BLE).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What happens in frequency hopping spread spectrum?
   A. The carrier stays fixed while power is varied
   B. The signal is sent on all 79 channels at once
   C. The receiver guesses the sequence
   D. The carrier changes frequency rapidly in a pseudo-random sequence known to both ends
   Answer: D. Both transmitter and receiver follow the same pseudo-random hop pattern. (Key point: Frequency hopping)

2. What are the Bluetooth hopping figures?
   A. 79 channels of 1 MHz, 1600 hops/s (625 us slots)
   B. 79 channels of 2 MHz, 800 hops/s
   C. 32 channels of 1 MHz, 1600 hops/s
   D. 79 channels of 1 MHz, 625 hops/s
   Answer: A. A new channel is used every 625 us, giving 1600 hops per second. (Key point: Bluetooth hopping figures)

3. What determines the hop sequence in a piconet?
   A. Each slave's own clock
   B. The master's device address and clock
   C. The Wi-Fi access point
   D. A random sequence chosen by each slave
   Answer: B. Because it comes from the master, all slaves follow the same pattern. (Key point: Hop sequence)

4. Which is an application of Bluetooth?
   A. Long-haul submarine cables
   B. Satellite uplink to GEO
   C. Wireless headsets and hands-free car kits
   D. Mains power distribution
   Answer: C. Bluetooth is a short-range radio used for headsets, file transfer and peripherals. (Key point: Applications)

## Related in other subjects

- [Spread spectrum: FHSS and DSSS](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aspread-spectrum-fhss-dsss) — Data Communication, chapter 6, asked 4×
- [Spread spectrum and FHSS](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aspread-spectrum-fhss) — Wireless Communication, chapter 4
- [Spread spectrum multiple access variants](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Assma-variants-applications) — Wireless Communication, chapter 7
- [OFDM principle and spread spectrum types](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aofdm-spread-spectrum-types) — Wireless Communication, chapter 4