A walkie talkie is similar to the smartphones we often use, it is a communication tool, but it is different from a mobile phone. What exactly is the working principle that makes walkie talkies different from mobile phones? How does a walkie talkie work?

1、 Working principle of walkie talkie - Introduction

Two way radio, invented by John Kermode in Westinghouse laboratory in the 1920s, is a two-way mobile communication tool that does not require any network support. It can be mainly divided into three categories: analog walkie talkies, digital walkie talkies, and IP walkie talkies, and has now been widely used.

2、 Working principle and classification of walkie talkies

There are various types of walkie talkies, which can be classified into handheld, vehicle mounted, fixed, and relay based on their usage; According to different communication modes, it can be divided into simplex communication walkie talkies and duplex communication walkie talkies; According to different technical designs, it can be divided into analog walkie talkies and digital walkie talkies; According to different equipment levels, it can be divided into amateur walkie talkies and professional walkie talkies; According to different communication services, it can be divided into public walkie talkies, data transmission walkie talkies, police walkie talkies, marine walkie talkies, aviation walkie talkies, etc.

3、 The working principle of each part of the walkie talkie

A walkie talkie mainly consists of four parts: transmission, reception, modulation, and signaling processing. The working principles of each part are as follows:

Transmitting part: After a person emits sound, a radio frequency carrier signal is generated through a phase-locked loop and a voltage controlled oscillator. Firstly, the signal is amplified by a buffer amplifier, an excitation amplifier, and a power amplifier; Secondly, after passing through a low-pass filter, harmonic components are eliminated; Finally, it is transmitted through the antenna.

Receiving part: The receiving part directly receives the amplified signal emitted by the transmitting part. Firstly, the signal is mixed with the first local oscillator signal from the phase-locked loop frequency synthesizer at the first mixer to generate the first intermediate frequency signal; Secondly, filtering is completed through a crystal filter; Again, mix with the second local oscillator signal at the intermediate frequency processing chip to generate a second intermediate frequency signal; Finally, the useless signal is filtered out by a ceramic filter, and after amplification and frequency discrimination, an audio signal is generated. The audio signal is further amplified, bandpass filtered, de emphasized, volume controlled, power amplifier and other circuits to drive the speaker to produce sound.

Modulation section: The modulation section mainly completes the function of converting language into electrical signals through microphones.

Signal processing: A portion of the low-frequency signal obtained after frequency discrimination is amplified and bandpass filtered before entering the CPU for comparison with preset values to control the output of the audio amplifier and speaker. When the preset value is the same, turn on the speaker, otherwise turn off the speaker.