Network Analysis and Feedback Amplifier Design.1 H . W. Bo d e. The material for this book was originally prepared as a text for an informal course at Bell Telephone Laboratories. I t is the outgrow th of a research directed a t the problem of designing degenerative feedback amplifiers to provide substantial feedback w ithout instability. The solution of the feedback problem is, however, dependent upon certain propositions in general network theory which are applicable also to other situations. With the addition of o ther logically related material, this has made the book arise in television, frequency modulation, multi-channel carrier telephone and other modern communication systems.
fh e emphasis on broad-band problems has a num ber of consequences.
01 example, it gives special importance to networks including resistances as \vcll as reactances, since it is frequently only by the use of controlled dissipation th a t netw ork characteristics can be made to vary smoothly er broad ranges. T he em phasis on broad-band applications also requires special attention to the effects of parasitic elements, and several sections of the book are devoted to the developm ent of design methods for networks mcluding prescribed parasites. A final consequence is the importance which is assumed by the lim itations on the characteristics which can be obtained from physical networks. Over very narrow bands only very mild mutations exist, b u t as the band becomes broader the available charac
teristics become more and more restricted.
fhe other principal point of emphasis of the book is on the use of net
160 BELL SYSTEM TECHNICAL JOURNAL
stage networks, and local feedback circuits, especially when they appear as constituents of a broad-band amplifier.
Judging Mica Quality Electrically.2 K . G. C o u tle e . A threatened mica shortage resulting from an unprecedented w artim e dem and for mica capacitors used in electronic com m unication equipm ent by the Armed Forces was forestalled by rigid conservation measures, use of alternate m aterials, and the use of electrically selected mica from types previously considered unsuitable for capacitor use. B y em ploying two electrical tests, developed by Bell Telephone Laboratories, Inc. for the W ar Produc
tion Board, in com bination with visual and physical requirem ents, mica was selected from plentiful stocks of lower visual quality types of mica, effec
tively increasing the supply of capacitor mica b y 60 per cent. This method of electrically judging the q uality of raw mica was given a thorough com
mercial trial and found both practicable and reliable.
A Simple Optical Method for the Synthesis and Evaluation of Television ImagesJ R . E . G rah am and F. W. R e y n o ld s. A com bination of a 35- m illim eter m otion-picture projector and a line screen enables the projection of still or motion pictures closely sim ilar in appearance to those produced by television. T his sim ilarity of appearance is checked theoreticallly by an analysis of the type previously reported b y M ertz an d G ray in a discussion of the theory of scanning. From the analysis it is shown th a t five para
m eters of the optical-sim ulation system m ay be varied to obtain the equiva
len t of variations in television factors such as num ber of scanning lines, size and configuration of scanning apertures, and w idth of frequency band.
Photographs of sim ulated television pictures projected by this method are presented. These pictures include subject m atte r of general interest as well as as selected subjects to illustrate the spurious detail com ponents in
troduced by the television scanning process. These com ponents produce moire p a tte rn s, “ steps” on diagonal lines, an d im pairm ent of vertical resolution. Simulation pictures projected by this m ethod have been com
p ared w ith those produced by a television system and the expected agree
, Proc. I. R. E. and IFares and Electrons, January 1946 (pp. 18W-30W).
ABSTRACTS 161 A Coil-Neutralized, Vacuum-Tube Amplifier at Very TIigh FrequenciesA R. J. K irc h e r. This p ap er describes a two-stage single-side coil-neutralized amplifier employing an experim ental triode operating in the vicinity of 140 megacycles. Circuit features are described and typical operating conditions are indicated. T ypical distortion characteristics a t low-power levels are also included. electrical feedback amplifiers can be applied a t once to servomechanisms and similar devices.
This book, which was originally intended to be a N ational Defense Re
search Committee report, is an introduction to the theory of linear servo
mechanisms, considered as a special application of the general theory of feedback amplifiers. The steady-state theory of the system s is taken as fundamental, and the various problems concerning the stability and per
formance of the system s are discussed in term s of it. In the several chap maintaining the effectiveness of the therm oplastic covering provided on buried toll cables for installation in areas where corrosion is anticipated.
It also describes the m ethod used to obtain the required supplemental electrical drainage for the T ranscontinental Cables across the G reat Salt Desert west of Salt Lake C ity where the low earth resistivity and high concentration of alkali salts preclude the use of rectifiers connected between cable sheath and a made ground generally employed for drainage purposes.
Such installations would result in negative potentials between cable and earth of sufficient m agnitude to create conditions conducive to cathodic corrosion of the lead sheath in the presence of an alkali salt electrolyte.
To provide electrical drainage w ithout incurring these excessive negative Potentials a method was developed utilizing the normal potential difference between zinc and lead as the source of drainage current. Tw enty-four Pound zinc bars of commercially available zinc, 99 per cent pure, were in
stalled directly in the ground a short distance from the cables a t 12-mile
i i ' 0?;.1- R- E ’ December, 1945.Published by D. Van Nostrand Company, Inc., New York, N. Y., 1940.
Corrosion, June 1945.
162 BELL SYSTEM TECHNICAL JOURNAL
intervals, m aking connection betw een the zinc anodes and the cable sheaths by buried wire. T he cable-to-earth potentials were appreciably affected throughout the entire 120 route miles across the G reat Salt D esert by this anodes offers an economical and satisfactory m eans for protecting buried cables against corrosion.
Transmission Networks for Frequency Modulation and Television.1 H a r
o ld S. O sb o rn e . Looking forw ard to a great post w ar expansion in the a rts of frequency m odulation and television this paper discusses plans of the Bell System for providing transm ission netw orks required for the inter
connection of broadcast stations. A review of cable and open-wire car
rier system s shows how developm ents for purely message telephone business have a t the same tim e p u t the Bell System in a position of being able a t the present tim e to m eet such netw ork transm ission requirem ents for frequency m odulation as the broadcasters m ay select as desirable. Coaxial develop
m ents are reviewed briefly, including the application of these developments to television transm ission. F u tu re developm ents, together with the coaxial construction plans now under way, are expected to provide by ab o u t 1950 a fairly com prehensive nationw ide netw ork of facilities capable of providing for such transm ission requirem ents as m ay be desired by the television developm ent offers the u ltim ate possibility of aid to the severely deafened in learning to speak correctly and to use the telephone by seeing ra th er than hearing the voice of the d istan t speaker. T he p a ttern s will also be of considerable interest in the fields of speech science and music.
7 Elec. Engg., November 1945.
8 Science, November 9, 1945; Bell Tel. Sys. Monograph B-1368.
ABSTRACTS OF TECHNICAL ARTICLES 163 General Formulas for “T ”- and “ II” - Network Equivalents,9 M y k il B.
R eed. This paper presents the developm ent of two sets of general formulas which determine a set of “ T ” or “ II” impedances equivalent to any linear, lumped-constant, four-term inal network.
Concerning IIalien’s Integral Equation for Cylindrical A nlennasN S. A.
S ch elk u n o ff. The main purpose of this paper is to explain the substantial quantitative discrepancy between H allen’s formula for the impedance of cylindrical antennas, and ours. Ila lle n ’s first approxim ation involves a tacit assumption th a t the an ten n a is short compared with the wavelength.
Since the subsequent approxim ations depend on the first, they are degraded by this initial assum ption.
The approxim ations involved in his integral equation itself are justified;
and, if properly handled, the equation yields results in much b e tte r agree comcal antennas as a supplem ent to a previous paper containing the outline of the method and the main results. In the course of the present discussion the theory of principal waves on cylindrical conductors is extended to include the case in which the diam eter is not small compared with the wavelength.
Research Revolutionizes Materials.1- J. R. T ow n send. A technological lesson to be drawn from defeated Germany is th a t whereas Germans had been noted for their fundam ental contributions to science, they were unable to compete with the U nited N ations in the field of applied science and particularly in high-speed production methods. Their defeat was due more to the overwhelming num ber than to the individual superiority of the arm s brought against then. The miracle of American production is based on a design related to obtaining the most from the process used, m aterials of uniform quality, and high-speed production m ethods using high-power autom atic m achinery. G erm any’s failure was due to standardizing too early and too inflexibly and this m eant th a t they could not compete with the steady improvements in the a rt. The usual procedure is the development of methods of test followed by collection of d ata and the formulation of specific requirem ents controlling the useful quality of the m aterial. M odem
A.S.T.M. Bulletin, December, 1945.
164 ABSTRACTS OF TECHNICAL ARTICLES
in d u stry is based upon such specifications because m aterials m ust be so con
trolled since the action of the m achine is unvarying. M odern statistical m ethods can be applied to provide the tolerances and allowances necessary to achieve a uniform product. T he work of the American Society for T esting M aterials broadly covers the field of research in m aterials, methods of test, and quality control. T he benefits of this work extend to v ast im
provem ent in process m ethods, more uniform and higher-quality material an d result in economic gains of extensive character. Three examples were cited illustrating extensive projects of great use to the w ar effort. These were the developm ent of requirem ents for sheet brass, which was applied specifically to production of cartridge cases, high-quality die-casting speci
fications resulting in the production of m any p a rts used in communication an d aviation equipm ent, and the developm ent of a m ethod of test for in
specting mica by an electrical ra th e r than a visual test. T his last resulted in a large economic saving of this scarce m aterial.
Infantry Combat Communications.13 R a lp h E. W ille y . Communica
tions w ithin an infantry division during com bat involve n o t only the efficient installation, operation and m aintenance of all m eans of communication norm ally provided an d adopted for specific functions b u t also the use of standard equipm ent in im provised m ethods ad ap a ted to the needs of the p articu lar situation. T he paper covers a brief description of th e major item s of signal equipm ent issued to an infantry division together with their norm al use. In addition, there is discussed the solution to m any field problem s based on the com bat experience of the w riter in Belgium, Holland and Germ any.
Interesting inform ation is given on the signal supply problem and combat losses over a six-month period of com bat. Im provised field radio-link in
stallations and rem ote controls for the protection of operating personnel are discussed briefly. Photographs included w ith the paper show pictorially the m ajority of the item s of equipm ent described.
13 Elcc. Engg., January, 1946. _ '
Contributors to this Issue
E liz a b e th J. A rm stro n g , M.A. in Geology, Bryn M aw r College, 1934;
Ph.D., 1939. L ecturer in Geology, B arnard College, 1938-41; Research Assistant, C olum biatU niversity 1941-42; N ational Research Council Fel
low, 1942-43; Bell Telephone Laboratories, 1943-. R ecently M iss A rm strong has been working on X -ra y studies of crystal strain and imperfections.
X-ray irradiation and twinning.
J. L. C la rk e , B.Sc. in Electrical Engineering, U niversity of London, 1909. Bell Telephone Com pany of Canada, 1910—; Transm ission Engineer,
velopment and Research D epartm ent, American Telephone and Telegraph Company, 1929-34; Bell Telephone Laboratories, 1934-. D uring his em gineering D epartm ent, W estern Electric Company, 1913-25; Bell Telephone Laboratories, 1925-. Form erly as Transmission Research Engineer and now as Transmission S tandards Engineer, M r. Johnson has long been en
gaged in work closely connected with all types of transmission network prob
lems. He is the au th o r of the book “ Transm ission Circuits for Telephonic
166 BELL SYSTEM TECHNICAL JOURNAL
to wood preservation. D uring the w ar period he was active in the protec
tion of electrical equipm ents against m oisture and fungi a tta c k when used in the tropics.
William W. Mum ford, B.A., W illam ette U niversity, 1930. Bell Tele
phone Laboratories, 1930-. M r. M um ford has been engaged in work that is chiefly concerned w ith ultra-short-w ave and microwave radio communica
tion.
\
A. L. Sa m u e l, A.B., College of E m poria (K ansas), 1923; S.B. and S.M.
in Electrical Engineering, M assachusetts In stitu te of Technology, 1926.
A dditional g rad u ate work a t M. I. T . and a t Columbia U niversity. In
stru cto r in E lectrical Engineering, M . I. T ., 192j6—28. M r. Samuel joined the Technical Staff of the Bell Telephone Laboratories in 1928, where he h as been engaged in electronic research and developm ent. Since 1931,
his principal interest has been in the developm ent of vacuum tubes for use a t ultra-high frequencies.
William C. Tin u s, B.S. in Electrical Engineering, T exas A. & M . College, 1928. Bell Telephone Laboratories, 1928-. F or ten years M r. T inus was engaged in the developm ent of radio com m unication ap p aratu s, principally for mobile use. In 1938 he organized and directed the first ra d a r develop
m ent work in the Laboratories. As Radio D evelopm ent Engineer he is now responsible for a num ber of ra d ar an d related electronic development projects for the A rm y and N avy.