Modulation and decompression device, commonly known as modem, is mainly based on modulation and demodulation techniques. The following is a detailed explanation of the principle of modems:

1、 Basic Definition

A modem is an abbreviation for a modulator or a demodulator, commonly known as a modem or "cat" in Chinese. It is an electronic device that can achieve the modulation and demodulation functions required for communication. It can translate the digital signals of a computer into analog signals that can be transmitted along a regular telephone line, and these analog signals can be received by another modem on the other end of the line and translated into a language that the computer can understand.


2、 Working principle

1. Modulation process

Definition: At the transmitter, convert digital signals used internally by the computer into analog signals that can be transmitted over telephone lines.
Implementation method:

Amplitude Modulation (AM): Representing a digital signal by changing the amplitude of a carrier signal.

Frequency Modulation (FM): Representing a digital signal by changing the frequency of a carrier signal.

Phase Modulation (PM): Representing a digital signal by changing the phase of the carrier signal.

Result: The modulated analog signal is transmitted through high-frequency radio waves, telephone lines, or other transmission media.

2. The demodulation process

Definition: At the receiving end, convert the received analog signal back to a digital signal so that it can be processed and decoded by the target device (such as a computer or telephone).
Implementation method: The demodulation process is opposite to the modulation process, using a method corresponding to the modulation to restore the analog signal to a digital signal.
Result: The demodulated digital signal is sent to the computer interface for reception and processing.


3、 Classification of modems

According to the connection method, it can be divided into internal and external types. The built-in modem has a small size and can be inserted into the slot on the motherboard during use; External modems have a large volume and can be connected to the communication interface of a computer when in use, making them portable.

According to transmission capacity, there are low-speed and high-speed options. Common modem speeds include 14.4Kbps, 28.8Kbps, 33.6Kbps, 56Kbps, etc.

4、 The working mode of the modem

Modems usually have three working modes: on hook mode, call mode, and online mode. When the phone line is not connected, it is in idle mode; Both parties communicate via phone, which is a form of communication; The modem is connected and data transmission is done online.

5、 Practical application

Modems are often used in personal computers to exchange data and programs with other computers, as well as to access online information service programs. When connected to the Internet, modems play an important role in converting computer digital signals into analog signals that can be transmitted over telephone lines, as well as converting received analog signals back to digital signals.

6、 Technological development

With the continuous development of communication technology, modems are also evolving. For example, Qualcomm's Snapdragon X70 is a modem that integrates 5G and AI processors, representing the latest advances in modem technology.

In summary, the principle of a modem is based on modulation and demodulation technology, which enables the conversion between digital and analog signals, thus enabling communication between computers and other devices.