摘要:

The paper describes a new method of determining electron trajectories in an electrostatic field. Information derived from a model electrode system in an electrolytic tank is passed automatically and continuously to a differential analyser, where the equations of motion of the electron are integrated and its trajectory is traced on an output table.Electric-field components in the tank are sampled by means of pairs of probes dipping into the electrolyte, and the voltage between the two probes of each pair is balanced automatically on a potentiometer and is thus converted into a shaft rotation which can be fed into the differential analyser. The output shafts from the differential analyser determine the mean position of the probes in such a way that it moves along the trajectory which is being plotted.Results obtained with apparatus based on these principles are described, and a detailed analysis of the factors affecting the overall accuracy is included in the paper. The conclusion is reached that the method is a promising one, but that a digital computor would give much more satisfactory results than the differential analyser which was used.

DOI:10.1049/pi-3.1952.0046

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The paper provides a short introduction to a new system of communication. An attempt is made to show how the system was evolved as a logical development from earlier systems, and to suggest how it may find useful practical application.A short review of the growth of technique and theory of communication demonstrates the continued search for new systems of high efficiency and leads inevitably to the conception that the ultimate theoretical efficiency of utilization of frequency bandwidth has now been established by Shannon. The view is taken, however, that practical systems still need to be developed in order to approach more nearly to ideal performance.A discussion of features of pulse-code modulation (p.c.m.)—the most efficient system in current use—shows how suspected deficiencies have led to suggestions for a new system of communication. Examination of this system, tentatively called the “ambiguous index system,” demonstrates that the suspected deficiencies were not, in fact, very real and that the purely theoretical performance of p.c.m. has not been improved upon. However, certain practical advantages are revealed, and it is suggested that one variation of the new system, which is very nearly equivalent to the theoretical 2-digit multiple-level p.c.m. system, could be of great value when insufficient frequency bandwidth is available for binary coding by as many as 6 digits.It is shown that the new system permits a new and satisfactory classification of the system commonly known as “pulsed f.m.” which represents a special case of the ambiguous index system, which, in turn, is very closely related to signal coding systems. Hence, the very high theoretical performance of pulsed f.m. is not in any sense anomalous.A modification of the pulsed f.m. system probably represents an almost ideal system of transmission for the case where the bandwidth available for transmission is only about twice that which would be required for single-sideband working.

DOI:10.1049/pi-3.1952.0050

出版商:IEE    

年代:1952

数据来源: IET

摘要:

Because of the great increase of speed of modern aircraft, there has arisen a need for the elimination of the drag of external aerials. A common form of the suppressed type of aerial is the slot cut in the metallic skin of the aircraft, the slot behaving in a manner which is complementary to that of the conventional dipole. Measurements of the polar diagrams of slots installed on both full-scale and model aircraft show that the types of polar diagram frequently required on aircraft can be obtained by use of slot aerials, for which there is some agreement between the measured polar diagrams and those estimated theoretically using ray and diffraction theories. Exact diagrams apparently have to be determined experimentally, because aircraft normally do not have simple shapes which are amenable to calculation. The installation of slots has provided no great difficulty at metre or shorter wavelengths, but their application at longer wavelengths will depend upon what can be achieved by matching devices, and upon the limit to which the aircraft structure can be suitably modified.

DOI:10.1049/pi-3.1952.0051

出版商:IEE    

年代:1952

数据来源: IET

摘要:

External wire aerials, which are usually employed at frequencies below 20 Mc/s for radio aids on aircraft, are not preferred on high-speed aircraft because of their drag and general mechanical unsuitability. It becomes necessary to include the aerials within the aircraft skin, when they are usually referred to as suppressed aerials.In the paper, information on well-known external wire aerials, such as fixed inclined wires (long and short), inverted-L wires, trailing wires and shunt-wire-fed wings, is compared with that obtained with various suppressed aerials. Some of the suppressed aerials have performances which compare favourably with the external wire types and in certain respects have apparently better electrical characteristics. In particular, aerials which are folded or near-end fed, or those which involve an insulated stabilizer unit, have a wide bandwidth and are reasonably efficient. The impedance characteristics of some of the suppressed aerials are such as to make their use suitable where it is required to cover frequencies lower than the h.f. band.For h.f. suppressed aerials, where the wavelength is comparable to the aircraft dimension, the view is held that an efficient suppressed aerial will require the excitation of either the whole aircraft or a large part of it. Various methods of excitation are discussed and experimental evidence is given. Since the stabilizer is usually the only vertical component, its use is contemplated for vertical polarization; similarly, the wings and horizontal units of the aircraft are considered for horizontal polarization.Measurements of the electrical characteristics of aircraft aerials present considerable difficulties. They are not often satisfactory on a grounded aircraft, and flights are very uneconomical for preliminary experiments. In order to overcome these difficulties, the method of scaling aerials on scale-model aircraft is widely used to determine the performance of both external and suppressed aerials. Some of the suppressed types of aerial which have shown satisfactory characteristics obtained with the scale models have been installed in aircraft, and successful long-range flights using these aerials in the 2–20 Mc/s communication band have been made.

DOI:10.1049/pi-3.1952.0052

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0056

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0057

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0058

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0059

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0060

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0061

出版商:IEE    

年代:1952

数据来源: IET