radio frequencies, and we are only going to touch on the highlights that affect wireless telephony. An amplifier has to deliver enough power over time. Consider the task of transmit- ting eight continuous radio signals of 6 W each. Normal intuition tells us that the to- tal power output would be 48 W, eight times 6 W, and this is usually the case. A radio power amplifier called on to transmit these eight signals has to be able to deliver a con- tinuous average power of 48 W without overheating. Sustained average power is a ba- sic and important component of amplifier specification. The amplifier also has to deliver the required amplitude, not just the average volt- age, but also the peak voltage. Let's consider a simple case of two uncorrelated 1-W signals transmitted from the one antenna and powered by one amplifier. The total average power is 2 W. Into a typical antenna load, a 1-W signal might have a peak of 10 V. Once in a while, the two 10-V peaks of the two signals line up so that the am- plifier is called upon to deliver 20 V. This is shown in Fig. 4.3. While a 20-V amplifier could handle a 4-W signal into the same antenna load, it takes a 20-V amplifier to send two 1-W signals. In this case we say that the amplifier requires a peak power Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. The Base Station Key Radio Concepts V (t) Figure 4.3 Peak versus average power. of 4 W and an average power of 2 W. We also say that we have a peak-to-average ratio of two. 4 As the number of signals k increases, the average power requirement increases in proportion to k, but the peak power requirement increases in proportion to k2. Ten 1-W signals require an average power of 10 W and a peak power of 100 W. Building a 100-W amplifier just to send 10 W seems like overkill. Another solution is to build 10 smaller amplifiers and use a radio combiner to add