Chapter 6. Older Technology
You might think with all the current excitement about wireless communications that the technology has been around for only a short time. Nothing could be further from the truth, which is the topic of this chapter: wireless technologies which have been around awhile. This chapter picks only three of these "older" technologies for discussion: broadcasting, radar, and satellite communication. But even among these three there is a lot of variation in technology and system design. These three were chosen as they represent a good cross section of the various applications of RF technology.
AM radio, which has been around since the early 1920s, is an example of broadcast technology, as are FM radio and television. Broadcast technology is a unique RF application in that it conveys information-wirelessly-from one point to many points, with little concern for a response from the intended receivers. Broadcasting is a one-way technology (which does not keep people from screaming at their televisions). Recently, there has been an assault on the broadcasters by those using a different wireless technology, namely, satellite service providers (also discussed in this chapter).
Radar technology, which has been around since the late 1930s, is an interesting form of RF communication. Unlike other forms of wireless communication, radar does not work by superimposing an information signal onto an RF carrier (through modulation). Instead, the information is contained in slight changes in the RF carrier imposed on it by the environment. As you will soon learn, these small changes can contain a lot of information about an object which the radar is following.
Today, radar is used almost everywhere: on the ground, in the air, and out in space. The availability of low cost RF electronics is enabling the use of radar technology in some surprising new places. The area experiencing the greatest impact from low-cost radar is the automobile industry. Some day in the not-so-distant future, all cars will come equipped with radar technology as a standard feature. (As far as I know, there is no plan to equip automobiles with missiles.)
Even satellite communication has been around since the early 1960s. It was first envisioned in the 1940s, but had to wait for technology to catch up to make it feasible. Satellites can be used for both one-way and two-way communications. If you have ever called someone in Hawaii (from outside the state), the call was routed by a satellite. And if you have ever watched a live sports event in a different time zone, that signal too was routed via satellite.
As you go through this chapter, you will see common themes among these three wireless technologies. You will notice that the Federal Communications Commission (FCC) in the United States and the International Telecommunications Union (ITU) everywhere else are responsible for allocating frequency for each application. You will see how each of these wireless applications can be described simply by a combination of a few of the basic RF building blocks discussed earlier in this book. This chapter also discusses the role that frequency plays in each system. In every case, the system is designed to use the latest technology to take full advantage of each particular system's frequency allocation.
The goal of this chapter is to help you understand, at a very basic level, the workings of wireless systems you are already familiar with. In each instance you are given an opportunity to "follow the signal" as it travels and to see what changes, if any, it undergoes during its journey. Once you understand the fundamental principals of these three technologies, you will have a general understanding of how all wireless systems work. Today's most sophisticated wireless technologies, like Doppler radar and low Earth orbit satellites, are merely refinements and improvements to these three basic systems.