How Does Bluetooth Work? 蓝牙是如何工作的？
Bluetooth technology uses a wavelength to transmit information; however, it only works over short distances. You may have noticed that if you are wearing wireless headphones and walk too far away from your smartphone, the signal either gets disrupted or is cut off altogether.
蓝牙技术使用波长来传输信息；但是，它只能在短距离内工作。您可能已经注意到，如果您戴着无线耳机并且离智能手机太远，信号要么断断续续，要么被彻底中断。
Bluetooth waves aren’t meant to travel very far. In fact, most Bluetooth devices have a maximum connectivity range of around 30 feet. That distance can be cut even shorter if there are obstacles between the two devices connected via Bluetooth.
蓝牙波并不意味着传播很远。事实上，大多数蓝牙设备的最大连接范围约为30英尺。如果通过蓝牙连接的两个设备之间存在障碍物，则该连接距离也会变得更短。
The Bluetooth standard has changed many times over the years, from Bluetooth 1.1 in 2002, Bluetooth 2.0 EDR (Enhanced Data Rates), the Bluetooth 3.0 HS (High Speed and Ultra-Wideband), to today’s Bluetooth 5.3 with direction and asset-tracking services.
多年来，蓝牙标准发生了多次变化，从2002年的蓝牙1.1、蓝牙2.0 EDR（增强数据速率）、蓝牙3.0 HS（高速和超宽带）到今天具有方向性和资产跟踪服务功能的蓝牙5.3版。
What’s interesting about Bluetooth connectivity is that it operates on varying frequencies. Bluetooth connectivity is safe and secure from hacking because the frequencies change hundreds of times per second. This is known as frequency hopping spread spectrum.
蓝牙连接的有趣之处在于它可以在不同的频率上实现运作。蓝牙连接具备安全性，不会受到黑客攻击，因为频率每秒变化数百次，这被称之为跳频（FHSS）。
关于蓝牙晶振选型：
蓝牙晶振常用频率：16MHz、24MHz、32MHz、40MHz等
蓝牙晶振常用封装：SMD1612、SMD2016、SMD3225等
特殊要求：抗超声波、牵引值（TS）、低功耗等
产SMD2016无源贴片晶振规格参数如下：
关于RF射频芯片的倍频及锁相环
Low crystal frequency ( 16 to 40 MHz and ±10 ppm frequency deviation)feeding a phase locked loop integrated into the RFIC. An internal PLL that pulls the frequency up.
晶振频率（16~40MHz/频偏±10ppm）送至 RFIC锁相环。内部PLL，将频率拉高。
Types of products that have Bluetooth capability: 具有蓝牙功能的产品类型：
- Smartphones智能手机
- Speakers扬声器
- Headphones/earbuds耳机/耳塞
- Computers/tablets/laptops电脑/平板电脑/笔记本电脑
- Smart watches智能手表
- Camera systems摄像系统
- Lighting systems照明系统
- Security systems安全系统
- Other consumer electronics其他消费类电子产品
拓展阅读：
What is frequency-hopping spread spectrum (FHSS)? 什么是跳频 （FHSS）？
Frequency-hopping spread spectrum (FHSS) transmission is the repeated switching of the carrier frequency during radio transmission to reduce interference and avoid interception.
跳频（FHSS）传输是在无线电传输过程中反复切换载波频率，以减少干扰并避免拦截。
