The Radioman's Manual of RF Devices, Principles and Practices
Dealing with the RF aspects of radio communication, this is an indispensable book for anyone involved in land mobile radio, ham radio, marine radio or aviation radio.
TABLE OF CONTENTS The Radioman's Manual of RF Devices, Principles and Practices
Chapter 1: RF Units of Measure
An understanding of the proper units of measure is essential to an understanding and application of the information and technology discussed in this book. Therefore, a thorough examination of special RF units of measure is presented here along with examples of applications.
1.1 The Decibel and Power Relationships
By definition, the decibel is one-tenth of a bel, named after Alexander Graham Bell. The bel is defined as a power ratio of 10:1. Since the response of the human ear is logarithmic, the bel is defined as the logarithm of the power ratio. The bel represents such a large power ratio that the decibel (dB) is commonly used to represent power ratios. Thus, 1 bel=10 decibels, or abbreviated 10dB. One decibel represents the approximate minimum detectable change in sound level for the human ear. The decibel relationship to change in power levels is expressed by the following formula:
where P 1 and P 2 represent the two power levels being compared. Think of the divisor bar as representing the expression compared to. In Equation 1.1 above, P 1 is compared to P 2. If P 1 is smaller than P 2, the decibel figure will be negative.
Figure 1 1: This RF amplifier has an input/output impedance of 50 ohms. The power input to the amplifier is 5 watts and the power output is 50 watts.
In order to avoid a negative solution, the larger level is used as the numerator and the smaller level...
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