求翻译：20世纪50~60年代，民用专业移动通信主要采用由点对点半双工通信的无线电对讲机来完成，通信的双方或多方在约定的频点使用对讲机完成通话。这种通信方式简单，无需基站设备，但通信距离有限。当用户一增多，问题就暴露出来，如频率不够使用，用户之间的相互干扰很多，通话没有任何私密性可言，基本不可能实现选择性呼叫。是什么意思？

50 to 60 years of the 20th century, mainly civilian professional mobile radio communication from the point half-duplex walkie-talkie to complete two or more parties to communicate the agreed use of radio frequency to complete the call. This communication is simple, no base station equipment, but the

In the 1950s and 1960s, civilian professional mobile communication is mainly used by the Point-to-point half-duplex communication over the walkie-talkie to complete, communication between two or more parties agree on the frequency of use of walkie-talkie completed calls. This form of communication b

20th century years, civilian professional mobile communication is mainly made by the ad-hoc half-duplex radio communication to complete communication between two or more parties in agreed frequency using the walkie talkie to complete calls. Such communication simple, without base stations equipment,