TABLE OF CONTENTS Communications receivers, with which we are primarily concerned in this book, have much in common with receivers for other applications, such as direction finders, radio altimeters, radar, and related systems. As mentioned in Chapter 1, the superheterodyne configuration is used for almost all applications and, therefore, the remainder of the book assumes such a design. Nevertheless, many of the receiver characteristics described in this chapter apply to other configurations as well.
The test receiver is one such application. In the recent past, conventional communications systems focused essentially on point-to-point transmissions. Now, however, a whole new range of configurations can be found. A good example is the use of a test receiver for performance measurements and maintenance work at a cellular telephone site, which in the extremes are located either in rural or densely-populated urban areas.
The dynamics of a cellular-type radio system introduce varied requirements and constraints upon the overall system. Effects introduced in such an environment include Doppler and severe multipath. Possible reflection elements for the RF radiation include fixed buildings, motor vehicles, and airplanes overhead-all of which disturb the path from the transmitter to the receiver. Fixed propagation has, thus, become a rare commodity. One of the reasons for moving to digital-based radios is to deal with these environmental uncertainties. Another is the increased channel capacity afforded by digital radio implementations.
The test receiver is an outgrowth-a necessity, if you will-of these trends. To serve its purpose, the test receiver must exceed the performance of the...
