It was said that a policeman in Australia had developed the first two-way radio used in vehicles in the early 1920s [1-3, 17]. However, it is still a matter of much controversy to regard who was the first to invent such radio. As users are getting more demanding and technologies are being developed, Private Mobile Radio continues to evolve from just voice to also include data communications; from conventional to trunked radio systems; from analogue to digital systems; to also employ cellular 4G/5G network technologies and etc. Nevertheless, the various developments of the Private Mobile Radio (except the use of cellular 4G/5G technologies) will not be discussed in this introductory article. This paper is only based on the most basic conventional Private Mobile Radio as it is better and easier to illustrate the principles and operation of the system. By the way, if you are a student, the author hope that this paper would arouse your interest in such systems, perhaps you may later consider pursuing a career in the field of radio communications. It is advancing very rapidly, providing good job opportunities, offering reasonable remuneration, and is also a real challenge to young people.
A mobile phone or cellular phone is nowadays indispensable to one’s everyday life. In Hong Kong, most people have a mobile phone or sometimes even more than one. Though 5G is a technical jargon, it has been becoming a common term for most ordinary people. Basically, a mobile phone user can make calls to other telephones or cellular phones. Fundamentally, they provide, in conjunction with the mobile telephone network and other systems etc., a “one-to-one” call. Both parties can speak and listen at the same time. Of course, it is also feasible to set up a conference call for three parties or more.