In the 1970s, China gave birth to a long-renowned radio station, which is called "small Bayi" 15-watt shortwave radio。The station carried out the transmission of information mainly by cryptography, that is, by sending Morse code by hand keys。

　　Sending code is essentially tapping with fingers, rhythmically sending pulse signals that pass and stop, and then changing into text information through a variety of combinations。A small code can carry a thousand words and command a thousand troops。

　　Hand-typing Morse code is a very old way of radio communication，Communication efficiency is also low，But because it's simple and easy to encrypt，It's easy to notice when you make a mistake，Shortwave radio also relies on ionospheric reflection to travel long distances (without relying on other means of relay)，You can communicate for hundreds of thousands of kilometers，But the frequency band is narrow，Low communication capacity)，So until now, it is still a very important means of communication for the armed forces of all countries。Our army, the US army, the Russian army, the French army, the ROK army, the Japanese Self-Defense Force and the Vietnamese Army all have reservations。It is worth mentioning that the communications Corps of our Army still regularly trains some of its personnel to be proficient in the operation of transmitters and Morse code, because in extreme circumstances, such as when the enemy destroys the communication facility first, the telegraph can be a critical means of communication。Therefore, in a complex electromagnetic environment, the telegraph may become the last means of communication because of its simplicity, reliability and low energy dependence。