Network analysis and feedback amplifier design | Date: 12 April 2011, 10:25
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Preface:
This book was originally written as an informal mimeographed text for one of the so-called "Out-of-Hour" courses at Bell Telephone Laboratories. The bulk of the material was prepared in 1938 and 1939 and was given in course form to my colleagues there in the winters of 1939-40 and 1940-41. During the war, however, the text has also been supplied as a reference work to a considerable number of other laboratories engaged in war research. The demand for the text on this basis was unexpectedly heavy and quickly exhausted the original supply of mimeographed copies. It has consequently been decided to make the text more widely available through regular channels of publication. In revising the material for publication, the original theoretical discussion has been supplemented by footnote references to other books and papers appearing both before and after the text was first written. In addition, an effort has been made to simplify the theoretical treatment in Chapter IV, and minor editorial changes have been made at a number of points elsewhere. Otherwise, however, the text is as it was originally written.
The book was first planned as a text exclusively on the design of feedback amplifiers. It shortly became apparent, however, that an ex:ensive preliminary development of electrical network theory would be necessary before the feedback problem could be discussed satisfactorily. With the addition of other logically related chapters, this has made the book primarily a treatise on general network theory. The feedback problem is still conspicuous, but the book also contains material on the design of non-feedback as well as feedback amplifiers, particularly those of wide band type, and on miscellaneous transmission problems arising in wide band systems generally. Much of this is material which has not hitherto appeared in previous texts on network theory. On the other hand, transmission line and filter theory, which are the primary concerns of most earlier network texts, are omitted.
Two further explanatory remarks may be helpful in understanding the book. The first is the fact that, although the feedback amplifiers envisaged in most of the discussion are of the conventional single loop, absolutely stable type, the original plan for the text called for two final chapters on design methods appropriate for multiple loop and conditionally stable circuits. Invincible fatigue set in before these chapters could be written. In anticipation of these chapters, however, the preliminary nalysis in the early portions of the book was carried forward in more general terms than would otherwise have been necessary. In Chapters IV-VI, particularly, this appreciably complicates the discussion, and the reader interested only in conventional feedback amplifiers can afford to omit the more difficult portions of these chapters.
The second general remark concerns the apparently unnecessary refinemerit to which the design methods described in the book are sometimes carried. This is explained by the fact that the amplifiers of particular interest to the class for which the notes were originally prepared were those used as repeaters in long distance telephone systems. Since a long system may include many repeater points, the cumulative effect of even quite small imperfections in individual amplifiers may be serious. Thus, the amplifier design requires more care than might be justified in an ordinary engineering application.
Under the circumstances in which the text was originally prepared, it naturally benefited by suggestions from many sources. I am indebted for such help to too many of my colleagues to enumerate individually. Special mention should, however, be made of Mrs. S. P. Mead for her assistance in the final preparation of the material for publication. It is a particular pleasure also to express my thanks to Dr. Thornton C. Fry, without whose support and encouragement the book could scarcely have been written.
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