Avionics Navigation Systems, 2nd Edition

4 Terrestrial Radio-Navigation Systems

4.1 INTRODUCTION

This chapter discusses the basic principles of terrestrial radio navigation systems, the radio propagation and noise characteristics and the major system performance parameters. The systems described in detail include all the important point source systems, such as direction finders, VOR, DME, and Tacan; and the hyperbolic systems, such as Loran-C, Decca, and Omega. All of these systems have been used worldwide and have provided accurate and reliable positioning and navigation in one or two dimensions for many years. In 1996 hundreds of thousands of civil and military aircraft throughout the world were equipped with these systems, and many of these will be used for years to come. Satellite radio nevigation systems (e.g., GPS) are discussed in Chapter 5 and military integrated radio communication–navigation systems are described in Chapter 6.

4.2 GENERAL PRINCIPLES

4.2.1 Radio Transmission and Reception

Figure 4.1 shows an elementary radio system. If a wire (antenna) is placed in space and excited with an alternating current of such frequency as to make the length of the wire equal to half a wavelength, almost all the applied ac power that is not dissipated in the wire will be radiated into space. A similar wire, some distance away and parallel to the first wire, will intercept some of the radiated power, and an appropriate detector connected to this receiving wire can indicate the magnitude, frequency, phase or time of arrival ...