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By Ulrich Rohde and Jerry Whitaker
Reviewed by Paul Danzer, N1II
ARRL Technical Advisor
(from QST, April 2001)
This is the third edition of this text published by McGraw-Hill, and when this major publisher prints a third edition you know a very large number of these books have been sold. As part of their telecommunications series, Communications Receivers--DSP, Software Radios and Design can be considered both a college textbook and a reference book.
It may come as surprise that even with over 700 pages, you probably cannot design a complete receiver based only on the material in this book. What the book does do is provide the understanding and background so you can go to one of the many references given and use the material there to do a modern design.
A generous background in math, including calculus, is required to under-stand many parts of the book. Whether you like it or not, modern receiver design re-quires college-level math to use and under-stand the equations.
Ulrich Rohde's name has appeared in both professional and Amateur Radio publications (including QST and QEX) for many years. He holds several advanced degrees including a Ph D. He was the Rohde in the German company Rohde & Schwartz, known for their advanced communications designs. In addition, he has been a professor at several US colleges and universities. He is also KA2WEU and DJ2LR.
Jerry Whitaker is called an "educator" in the publisher's biography. He is the award-winning editor and author of over a dozen books on communications and electronics, so perhaps educator is a good way to describe him.
Both authors have a record of innovation and technical excellence, and it is reflected in Communications Receivers--DSP, Software Radios and Design. So, with this parentage, we have just two questions: (1) What's in the book? and (2) Should I buy it?
There is a lot to find in Communications Receivers--DSP, Software Radios and Design. There is a little bit of history that probably allows newer engineers to under-stand that good results can be obtained with relatively few parts and an unsophisticated design. The text then branches out into just what you might expect--advanced waveforms, modulation schemes, digital radio design, DSP and the whole group of new design technologies that let us take advantage of integrated circuit parts.
The modulation review in the first chapter runs through what are today's common and not-so-common modulation schemes. Integral equations, block diagrams, spectra drawings, waveform drawings and Argand plots are used to illustrate the advantages and limits to both digital and analog modulation techniques. The results of analog-to-digital conversions and various digital filters are given with many illustrative drawings. Therefore, when you get a little further into the chapter and see a schematic of an early vacuum-tube receiver, using 215As and a UX-120, the use of 1930s symbols catches your attention!
The Radio Receiver Characteristics chapter shows impulse responses and channel characteristics by using a set of terrain drawings. The result of bounces, reflections and vectorial addition of multiple paths are both illustrated and discussed. The chapter serves to define the basic receiver requirements for controls, performance, BER and reception quality.
Chapter 3 lays out the calculations and requirements for noise figure. Unfortunately, it was not always apparent what each symbol meant--but if you really want to go into noise, spurious responses and various types of filtering, this is certainly a chapter to read. The list of references at the end of this and most chapters is extensive. Those at the end of this chapter included both Amateur Radio publications and professional engineering publications, with dates from 1935 to the present.
Antennas are dealt with in a way somewhat different from most antenna texts. Plots include both calculated and measured data, and there is stress on non-resonant very short whips and matching these non-optimal antennas. There is an interesting drawing of the field strength surrounding a cell phone, but the text is a bit sparse here and it doesn't state if the simulation shown assumes a hand was holding telephone or if the phone was near an equally simulated head.
I spent quite a bit of time going through Chapter 5, Amplifiers and Gain Control. I was caught by the representation of an AGC loop as a classical one-path control loop, and the similarity to a standard linear control system. Yes, I had to pull out some old textbooks to understand some of it, but it sure was interesting!
Receiver buffs will find a lot of schematics and comparisons in the Mixer chapter. Conventional, single-chip solid state and microwave mixers are all surveyed. The chapter concludes with almost three and one half pages of references--so you might get the impression that there is a lot more to be said on this topic!
Approximately 126 pages are spent on frequency control and local oscillators. It is obviously comprehensive and I thought it was quite readable. Despite the 126 pages, four pages of references are given.
If I wanted more pages at any point, I would have asked for more on noise blanking. This is a problem that has only occasionally been solved for amateur-type communication. Where the information received is digitally coded, perhaps this is less of a problem then in the "old AM and SSB" days, but heavy noise plays havoc even with error-correcting digital communication loops. However, there are a number of interesting block diagrams and discussions of diversity reception in the same chapter, so I guess you just can't fit everything into one book.
The last chapter of the book is titled Receiver Design Trends. If anyone has the right to try a crystal ball, these two authors have that right. I found it interesting that they seemed to concentrate on spectrum occupancy and bandwidth rather than with questions on components or design techniques. Perhaps there is a message there.
So, should you buy Communications Receivers--DSP, Software Radios and Design? If you are a professional in the field, you may already own an earlier edition and probably want to compare this edition. Many hams, however, belong to a club that maintains a library. There are often a number of editions of The ARRL Handbook for Radio Amateurs, The ARRL Antenna Book and HF Radio Systems and Circuits by Sabin and Schoenike (reviewed here in May 1999--you didn't miss that goody, did you?). Due to its specialization and complexity, most hams will probably opt to have an accessible copy in their public library, club library or the library of a local college. True receiver design buffs will, however, have to make their own decisions!
