TABLE OF CONTENTS This chapter covers some of the basic electromagnetic and transmission concepts that are required for the design, engineering, and implementation of satellite transmission systems. Other topics are covered in the chapters that follow. This chapter only presents a basic introduction to these topics and focuses pragmatically only on commercial satellite applications. Many of the topics addressed here would require an entire textbook to cover the discipline in a more complete manner.
The concept of decibel (dB) is fundamental to a discussion of transmission. One has
where P2 /P1 represents the ratio of power values.
(Bel is a relatively large unit, [1] hence the smaller unit, the decibel is used; 10 decibels = 1 bel.) Typically,
where P out is the power after an amplification stage or at the far end of a transmission link, and P in represents the input or initial power. P1 ( P in)is usually the reference power. As it can be plainly seen from the definition, the decibel does not in itself indicate power but is a ratio or comparison between two power values. When the ratio is positive, one uses the term gain. If P2 ( P out) is less than P1 ( P in), the ratio is less than 1.0, and the resultant value in decibels is negative. For example, if P2 is one-tenth of P1, then dB = 10 log (0.1/1) = -10...
