Chapter 12: Terrestrial Radio Communication Systems

---

Terrestrial radio as a transmission medium is attractive when the terrain does not permit laying of cables. To cover hilly areas, areas separated by lakes, rivers, etc., terrestrial radio is used for local loops and trunks. For providing telecommunication facilities to remote/rural areas, again radio is the best option. To avoid digging up the roads, even in urban areas, radio systems are being used. Radio has another advantage—it provides the capability of mobility to the users. For broadcasting applications, radio is the best choice because radio waves travel long distances. In this chapter, we will study some representative terrestrial radio systems—broadcasting systems, wireless local loops, cordless telecommunication systems, and trunked radio systems.

12.1 ADVANTAGES OF TERRESTRIAL RADIO SYSTEMS

As compared to the guided media such as twisted pair, coaxial cable, and optical fiber, terrestrial radio has many advantages:

• Installation of radio systems is easier compared to cable because digging can be avoided. The radio equipment has to be installed only at the two endpoints.

• Maintenance of the radio systems is also much easier as compared to cable systems. If the cable becomes faulty, it is difficult to locate the fault and more difficult to rectify the fault.

• Radio provides the most attractive feature—mobility of the user. Even if the user is moving at a fast pace in a car or even in an airplane, communication is possible.

• Radio waves can propagate over large distances. The coverage area depends on the frequency band. HF waves can travel hundreds of kilometers, VHF and UHF systems can cover up to 40 kilometers, and microwave systems can cover a few kilometers. With the use of repeaters, the distance can be increased.

Terrestrial radio as the transmission medium has the following advantages: easy installation, easy maintenance, and ability to cover large distances. Another main attraction of radio is that it provides mobility to users.

However, while designing a radio system, the following need to be taken into consideration:

• Radio wave propagation is affected by many factors—the natural terrain (hills, mountains, valleys, lakes, seashores, etc.), artificial terrain (multistoried buildings), and weather conditions (rainfall, snow, fog).

• Radio waves are subject to interference with other radio systems operating in the same vicinity. Radio waves are also affected by power generation equipment, aircraft engine noise, etc.

• Radio waves are attenuated as they travel in the atmosphere. This loss of signal strength is known as path loss. To overcome the effect of path loss, the radio receiver should have high sensitivity—it should be capable of receiving weak signals and amplifying the signal for later decoding.

In designing radio systems, the following aspects need to be taken into consideration: propagation characteristics, which vary for different frequencies, based on the terrain; interference with other radio systems, and path loss.

Note 

The path loss in a radio system is the cumulative loss due to the attenuation of the signal while traveling in the free space and the attenuation in the various subsystems such as the filters, cable connecting the radio equipment to the antenna, etc.

---