TABLE OF CONTENTS There are two basic types of signals, analog and digital. Until recently, most radio systems exclusively transmitted analog signals. Over the past 10 years, many systems have started transmitting digital signals over the radio channel.
An analog signal is a signal that can vary continuously between a maximum and minimum value. An analog signal can assume an infinite number of values between the two extremes.
Figure 1.3 shows a sample analog signal created by sound pressure waves. In this example, as the sound pressure from a person's voice is detected by a microphone, it is converted to its equivalent electrical signal. Also, the analog audio signal continuously varies in amplitude (height, loudness, or energy) as time progresses.
Digital signals consist of a series of ones and zeros, most often represented in telecommunications signals by two different voltages. For example a +5 Volt level could represent a logical 1 (one) and 0 Volt level could represent a logical 0 (zero). The ones and zeros are called bits. Several bits (usually eight) are grouped into a byte and each byte is defined to have a specific meaning, such as a specific letter on a keyboard. Digital signals are used to represent specific levels on an analog signal. While a digital signal cannot represent every point on an analog wave, they can come close enough to be almost indistinguishable. Digital signals are much easier to process by computer systems and they are able to resist...
