Showing papers in "Bell System Technical Journal in 1947"

Probability functions for the modulus and angle of the normal complex variate

Abstract: This paper deals mainly with various ‘distribution functions’ and ‘cumulative distribution functions’ pertaining to the modulus and to the angle of the ‘normal’ complex variate, for the case where the mean value of this variate is zero. Also, for auxiliary uses chiefly, the distribution function pertaining to the reciprocal of the modulus is included. For all of these various probability functions the paper derives convenient general formulas, and for four of the functions it supplies comprehensive sets of curves; furthur, it gives a table of computed values of the cumulative distribution function for the modulus, serving to verify the values computed by a different method in an earlier paper by the same author.1

Polyrod antennas

Abstract: The polyrod, a new form of microwave endfire antenna, is described. This consists of a properly shaped dielectric rod protruding from a metal waveguide. For applications requiring moderate gain, it possesses desirable electrical and mechanical properties. It is useful as a unit antenna in broadside arrays on account of its low crosstalk into adjacent polyrods. This paper describes work done from 1941 to 1944 at the Bell Telephone Laboratories, Holmdel, N. J. Important individual contributions are acknowledged in some of the footnotes. A report of this development has been withheld from earlier publication for reasons of military security.

Properties and uses of thermistors — Thermally sensitive resistors

Abstract: A new circuit element and control device, the thermistor or thermally sensitive resistor, is made of solid semiconducting materials whose resistance decreases about four per cent per centigrade degree. The thermistor presents interesting opportunities to the designer and engineer in many fields of technology for accomplishing tasks more simply, economically and better than with available devices. Part I discusses the conduction mechanism in semiconductors and the criteria for usefulness of circuit elements made from them. The fundamental physical properties of thermistors, their construction, their static and dynamic characteristics and general principles of operation are treated. Part II of this paper deals with the applications of thermistors. These include: sensitive thermometers and temperature control elements, simple temperature compensators, ultrahigh frequency power meters, automatic gain controls for transmission systems such as the Types K2 and L1 carrier telephone systems, voltage regulators, speech volume limiters, compressors and expandors, gas pressure gauges and flowmeters, meters for thermal conductivity determination of liquids, and contactless time delay devices. Thermistors with short time constants have been used as sensitive bolometers and show promise as simple compact audio-frequency oscillators, modulators and amplifiers.

Telephony by pulse code modulation

Abstract: An experiment in transmitting speech by Pulse Code Modulation, or PCM, is described in this paper. Each sample amplitude of a pulse amplitude modulation or PAM signal is transmitted by a code group of ON-OFF pulses. 2n amplitude values can be represented by an n-digit binary number code. For a nominal 4 kc. speech band these n ON-OFF pulses are transmitted 8000 times a second. Experimental equipment for coding the PAM pulses at the transmitter and decoding the PCM pulses at the receiver is described. Experiments with this equipment indicate that a three-unit code appears to be necessary for a minimum grade of circuit, while a six- or seven-unit code will provide good quality.

Targets for microwave radar navigation

Abstract: The effective echoing areas of certain radar targets can be calculated by the methods of geometrical optics. Other more complicated structures have been investigated experimentally. This paper considers a number of targets of practical interest with particular emphasis on trihedral and biconical comer reflectors. The possibility is indicated of using especially designed targets of high efficiency as aids to radar navigation.

Development of silicon crystal rectifiers for microwave radar receivers

Abstract: To Those not familiar with the design of microwave radars the extensive war use of recently developed crystal rectifiers1 in radar receiver frequency converters may be surprising. In the renaissance of this once familiar component of early radio receiving sets there have been developments in materials, processes, and structural design leading to vastly improved converters through greater sensitivity, stability, and ruggedness of the rectifier unit. As a result of these developments a series of crystal rectifiers was engineered for production in large quantities to the exacting electrical specifications demanded by advanced microwave techniques and to the mechanical requirements demanded of combat equipment.

Radar antennas

Abstract: Radar proved to be one of the most important technical achievements of World War II. It has many sources, some as far back as the nineteenth century, yet its rapid wartime growth was the result of military necessity. This development will continue, for radar has increasing applications in a peacetime world.

Some results on cylindrical cavity resonators

Abstract: Certain hitherto unpublished theoretical results on cylindrical cavity resonators are derived. These are: an approximation formula for the total number of resonances in a circular cylinder; conditions to yield the minimum volume circular cylinder for an assigned Q; limitation of the frequency range of a tunable circular cylinder as set by ambiguity; resonant frequencies of the elliptic cylinder; resonant frequencies and Q of a coaxial resonator in its higher modes; and a brief discussion of fins in a circular cylinder. The essential results are condensed in a number of new tables and graphs.

Reflex oscillators

Abstract: The reflex oscillator is a form of long-transit-time tube which has distinct advantages as a low power source at high frequencies. It may be light in weight, need have no magnetic focusing field, and can be made to operate at comparatively low voltages. A single closed resonator is used, so that tuning is very simple. Because the whole resonator is at the same dc voltage high frequency by-pass difficulties are obviated.

Tables of phase associated with a semi-infinite unit slope of attenuation

Abstract: This paper presents tables of the phase associated with a semi-infinite unit slope of attenuation The phase is given in degrees to 001 degree with an accuracy of ± 001 degree and in radians to 00001 radian with an accuracy of ± 000015 radian The method of constructing the tables and a brief analysis of the errors are given An appendix, which gives a detailed explanation with specific examples of the use of the tables in determining the phase associated with a given attenuation characteristic or the reactance associated with a given resistance characteristic by means of the straight line approximation method given in Bode's “Network Analysis and Feedback Amplifier Design,” is included for the benefit of those who are not already acquainted with this method The Appendix also presents an example of a non-minimum phase network1 in which the minimum phase determined from the attenuation characteristic fails to predict the true phase of the network

First and second order equations for piezoelectric crystals expressed in tensor form

Abstract: Aeolotropic substances have been used for a wide variety of elastic piezoelectric, dielectric, pyroelectric, temperature expansive, piezo-optic and electro-optic effects. While most of these effects may be found treated in various publications1 there does not appear to be any integrated treatment of them by the tensor method which greatly simplifies the method of writing and manipulating the relations between fundamental quantities, Other short hand methods such as the matrix method2 can also be used for all the linear effects, but for second order effects involving tensors higher than rank four, tensor methods are essential. Accordingly, it is the purpose of this paper to present such a derivation. The notation used is that agreed upon by a committee of piezoelectric experts under the auspices of the Institute of Radio Engineers.

The biased ideal rectifier

Abstract: Methods of solution and specific results are given for the spectrum of the response of devices which have sharply defined transitions between conducting and non-conducting regions in their characteristics. The input wave consists of one or more sinusoidal components and the operating point is adjusted by bias, which may either be independently applied or produced by the rectified output itself.

End plate and side wall currents in circular cylinder cavity resonator

Abstract: Formulas are given for the calculation of the current streamlines and intensity in the walls of a circular cylindrical cavity resonator. Tables are given which permit the calculation to be carried out for many of the lower order modes.

Precision measurement of impedance mismatches in waveguide

Abstract: A method is described for determining accurately the magnitude of the reflection coefficient caused by an impedance mismatch in waveguide by measuring the ratio between incident and reflected voltages. Reflection coefficients of any value less than 0.05 (0.86 db standing wave ratio) can be measured to an accuracy of ± 2.5%.

The radar receiver

Abstract: The spectacutar development of radar during World War II remains an outstanding achievement in the history of communications and the allied electronic sciences With military necessity furnishing the required driving force and through the full interchange of technical knowledge among all interested workers in this field, it has been possible to extend our visual senses far beyond the horizons considered quite inelastic only a few years ago The potentialities of radar in the peacetime world and the future application of radar design principles and techniques to the communications and allied fields justify a review of some further details of this wartime development

Spectrum analysis of pulse modulated waves

Abstract: The problem here is to find the frequency spectrum produced by the simultaneous application of a number of frequencies to various forms of amplitude limiters or switches. The method of solution presented here is to first resolve the output wave into a series of rectangular waves or pulses and then to combine the spectrum of the individual pulses by vectorial means to find the spectrum of the output. The rectangular wave shape was chosen here as the basic unit in order to make the method easy to apply to pulse modulators.

High-vacuum oxide-cathode pulse modulator tubes

Abstract: In Practically all pulsed oscillators such as those used in radar, some means must be provided to apply the pulse voltage to the oscillator circuit. In many early radars, a high-vacuum modulator was used for this purpose. The pulse was generated at low power level and then amplified by means of one or more stages employing high vacuum tubes. The final stage was required to block, or cut off the d-c supply voltage with no pulse applied, and to permit as much as possible of the d-c voltage to appear on the oscillator during the pulse. Since most radar oscillators operate at pulse voltages of from 5 to 20 kv and require currents of several amperes during the pulse, the requirements of the modulator tubes are quite severe. Standard transmitting1 tubes were used at first, the higher power tubes having the necessary voltage rating and having in general a fair amount of cathode emission. Tubes were operated in parallel to provide the required amount of current. Practically all of these tubes were of the thoriated tungsten filament type. For example an early army radar, the SCR268,2 employed 8 tubes in parallel having a total filament power of 1040 watts to provide a pulse current of about 10 amperes. The use of such equipment in portable or airborne service would be obviously impractical because of the large power consumption, bulk, and weight. In an attempt to provide tubes more suited to this type of service, those described in this paper were developed.