DOI:10.1049/ji-3-2.1946.0002

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper deals with the theory and design of the non-linear Wheat-stone bridge circuits used in voltage stabilizers. It is restricted to the use of the bridge as a source of voltage proportional to the change in the supply voltage and to non-linear elements obeying the lawV=kIn, wherenandkare constants. Four circuits are considered, and formulae are deduced for the general case of a resistive load across the output terminals. The effect of changes in the various parameters is discussed. Formulae are also given for the load required for maximum power output from the bridge for a given change in input voltage. The paper concludes with a review of the advantages and disadvantages of the various circuits.

DOI:10.1049/ji-3-2.1946.0005

出版商:IEE    

年代:1946

数据来源: IET

摘要:

On the basis of an exponential build-up of oscillations in its grid circuit, the super-regenerative phenomenon is analysed and a general expression for the output at modulation frequency is obtained. This expression is examined term by term and reveals the mechanism of (a) high amplification, (b) self-a.v.c. action, (c) excessive distortion of the modulation frequency at modulation depths in excess of 50%. All these properties are quite characteristic of the super-regenerative detector in practical operation.Histograms illustrate the distortion effect in terms of modulation depth. Various oscillograms verify the mathematical results, particularly in regard to the law of build-up of oscillations as a function of the amplitude of the applied signal.The dependence of radio-frequency selectivity and modulation-frequency gain upon the quenching frequency is shown in the analysis and verified by measurements. It is shown that an optimum quenching frequency exists for maximum gain at the modulation frequency. If this optimum frequency is slightly exceeded, the noise background may be removed without severe reduction of gain.The ability of the super-regenerative detector to discriminate agamst impulsive radio-frequency interference (e.g. motor-vehicle igmtion interference) is analysed briefly. The reception of frequency-modulated signals is also discussed briefly.

DOI:10.1049/ji-3-2.1946.0006

出版商:IEE    

年代:1946

数据来源: IET

摘要:

Consideration is given to the various electrical quantities associated with the equivalent network of a quartz crystal which might be used to assess the “activity” that the crystal will exhibit in an oscillator circuit. It is concluded that the most generally serviceable criterion is afforded by measuring the anti-resonant impedance of the parallel combination of mounted crystal and a standardized value of capacitance typical of that encountered in current oscillator designs. This is especially true for the high-frequency thickness-shear-mode plates which at present constitute the bulk of the output of the industry, since these plates are practically always used in circuits in which this anti-resonant impedance determines directly the amplitude of oscillation.The relations between the various possible criteria of activity are investigated.The following pieces of equipment are described:—1. A flexible laboratory instrument capable of measuring the series-resonant or anti-resonant impedance of any crystal response in the frequency range 50 kc/s–20 Mc/s.2. A simpler laboratory instrument capable of measuring the anti-resonant impedance of any response in a restricted frequency band around selected spot frequencies.3. An instrument designed for factory or other routine testing, in which the parallel dynamic resistance of the dominant crystal response is measured by a substitution method in an oscillator circuit. This instrument is suitable for frequencies above 3 Mc/s.4. An instrument similar to No. 3 but slightly more complex, for the frequency range 80 kc/s–3 Mc/s.

DOI:10.1049/ji-3-2.1946.0007

出版商:IEE    

年代:1946

数据来源: IET

摘要:

Random fluctuations in the amplitude of an electric current were originally discovered in two different circumstances: (a) the fluctuation in the current through a thermionic valve, which is known as “shot noise,” and (b) the voltage fluctuation at the terminals of a resistor, which is known as “Johnson noise.” The theory of these two types of fluctuation is presented in outline form; and it is shown how these two aspects of the fundamentally discrete nature of the flow of electric current, when it is a stream of electrons, can be unified into a single theory of current fluctuations due to random motions of the electrons. The theory is applied also to the controversial case of a space-charge-limited thermionic valve. Subsidiary factors, such as partition of current in a screen-grid valve and the behaviour of secondary-emission amplifiers, are of great technical importance, and methods of estimating the magnitude of their effects are described. The equivalent temperature of the radiation resistance of an aerial is also considered.

DOI:10.1049/ji-3-2.1946.0008

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper presents a fundamental theory of noise which the authors believe to be physically perspicuous and from which all the well-established formulae used in practice can be deduced by direct mathematical argument. Since these formulae almost all relate to mean-square noise in linear circuits, the theory will not be applied here to other problems, although its ideas are valuable in attacking more complicated problems.The subject is discussed under the following headings: (1) Introduction; (2) the basic postulate and the fundamental equations; (3) the “mean theorem” and the “mean-square theroem” (4) the calculation of mean-square noise; (5) thermal noise; (6) application to valve and circuit noise; (7) space-charge effects; and (8) transit-time effects.

DOI:10.1049/ji-3-2.1946.0009

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper deals with the theory and experimental development of resonator systems suitable for measurement of the permittivity and power factor of solid dielectric materials in the wavelength range below 50 cm (600 Mc/s). The relative suitability of three forms of resonator, namely a short-circuited length of coaxial transmission line operating in the principal mode, and hollow cylindrical cavity-resonators operating respectively in the E010and H01nmodes, is discussed. The theory governing the resonant behaviour of these systems when wholly and partially filled with “lossy” dielectric is developed, leading to relations connecting the permittivity and power factor of the latter with the resonant wavelength and Q-factor respectively.

DOI:10.1049/ji-3-2.1946.0010

出版商:IEE    

年代:1946

数据来源: IET