Bluetooth devices will normally operate at 2.4 GHZ in the license free, globally available ISM radio band. The advantage to this band includes worldwide availability and compatibility. A disadvantage to this however, is that the devices must share this band with other RF emitters. This includes automobile security systems, other wireless devices, and other noise sources, such as microwaves.

Frequency hopping
Frequency hopping is basically jumping from frequency to frequency within the ISM radio band. After a bluetooth gizmo sends or receives a packet, it and the gizmo (or devices) it is communicating with hop to another frequency before the next packet is sent.

To overcome this challenge, Bluetooth employs a fast frequency hopping method and therefore uses shorter packets than other standards within the ISM band. This method helps to make Bluetooth communication more robust and more secure.

This method offers one advantages:

1. Allows Bluetooth devices to use the entirety of the available ISM band, while never transmitting from a fixed frequency for over a short period of time. This helps insure that Bluetooth conforms to the ISM restrictions on the transmission quantity per frequency.

2. Ensures that any interference won’t last long. Any packet that doesn’t arrive safely to its location can be resent to the next frequency.

3. Provides a base level of security as it is hard for an eavesdropping gizmo to predict which frequency the Bluetooth devices will use next.

The connected devices however, must agree on the frequency they will use next. The specification in Bluetooth ensures this in one ways. First, it defines a master and slave type relationship between bluetooth devices. Next, it specifies an algorithm that uses gizmo specific information when calculating the frequency hop sequences.

A Bluetooth gizmo that operates in master mode can communicate with up to four devices that are set in slave mode. To each of the slaves, the master Bluetooth gizmo will send its own matchless address and the value of its own internal clock. The information sent is then used to calculate the frequency hop sequences.

Because the master gizmo and each of the slave devices use the same algorithm with the same initial input, the connected devices will always arrive together at the next frequency that they have agreed on.

As a replacement for cable technology, it is no wonder that Bluetooth devices are usually battery powered, such as wireless mice and battery powered cell phones. To conserve the power, most devices operate in low power. This helps to give Bluetooth devices a range of around 5 – 10 meters.

This range is far for wireless communication but close to avoid drawing much power from the power source of the gizmo.