DOI:10.1049/pi-3.1949.0001

出版商:IEE    

年代:1949

数据来源: IET

摘要:

An account is given of work carried out at the Telecommunications Research Establishment on the design and use of Yagi aerial arrays during the period 1938–42. An attempt is made to give sufficient information in tabular form for an aerial of given characteristics to be designed approximately. Final adjustment by experiment will be required unless a previous design is copied exactly.The advantages and limitations of multiple Yagi arrays are considered and a simple theoretical explanation of the mode of operation of a Yagi aerial is given. The types of polar diagram obtained when the design parameters are changed are deduced from vector diagrams. Only aerials of length greater than one wavelength are considered. These normally consist of three or more directors in addition to an exciter and a reflector.

DOI:10.1049/pi-3.1949.0002

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper describes measurements, at a frequency of 1 000 c/s, of the capacitance changes in air capacitors due to moisture in the atmosphere. It is shown that these changes may be considerably in excess of those due to the alterations in the permittivity of the air. Over the range of relative humidity 30–65% the total change in capacitance can be about 3 parts in 10 000 at room temperatures. The full advantage of the otherwise high stability of a precision air capacitor is lost when this effect is ignored.

DOI:10.1049/pi-3.1949.0003

出版商:IEE    

年代:1949

数据来源: IET

摘要:

A test set has been developed which enables the degree of impedance irregularity of a high-frequency coaxial cable to be measured in terms of the return loss of echo pulses reflected from the irregularities when short pulses of carrier frequency are fed into the cable. The tester described employs pulses 0.3 microsec long, of a carrier frequency of 20 Mc/s, and can measure echo return losses of up to 90 db.

DOI:10.1049/pi-3.1949.0004

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper describes a type of directional coupler called a reflectometer used for connecting test equipment to a radio-frequency transmission line. A single loop of wire with a resistor in one arm is mounted at a fixed point and is loosely coupled to both the electric and the magnetic fields of waves in the line. The relative phase of the two fields for a travelling wave depends upon the direction of propagation, and the couplings with these fields are arranged to cancel for one direction of propagation and add for the other. Thus the coupling will detect, or launch, waves travelling in one direction only.This type of coupler was used originally in America to measure the reflected waves in a 400-Mc/s coaxial feeder: hence the name “reflectometer.”1, 2In the present paper the general theory is given, and a design suitable for waveguides at a wavelength of 10 cm is described. Applications to the monitoring of standing waves and transmitted power in a radar transmitter system and to the testing of radar receiver sensitivities are considered, and the methods which make use of a reflectometer are shown to have considerable advantages over others.

DOI:10.1049/pi-3.1949.0006

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The subject of radio field-strength measurement is of direct interest in connection with all applications of radio wave technique. Furthermore, since radiocommunication, broadcasting and, to a lesser extent, navigational aids concern many countries other than that in which the service originates, it is important to ensure that there is international agreement on the methods of measurement used and on the results obtained with the equipment available. The British National Committee for Scientific Radio has been active in this field in connection with the General Assemblies of the Union Radio Scientifique Internationale since 1934, when a comprehensive review of the then existing methods of measuring radio field strengths was presented. Two years later, the National Physical Laboratory conducted a comparison between the various field-strength measuring sets then available in Great Britain for wavelengths between 7 and 1 500 m (40 Mc/s and 200 kc/s). The results of this comparison showed that while in the wavelength band 6 to 10 m (50 to 30 Mc/s) the measurements on different sets agreed to within ±20% of the mean value, greater divergences were obtained at longer wavelengths; and in the range 100 to 500 m (3 to 0.6 Mc/s) the departures from the mean value of field strength ranged from −30% to +60%. An examination by the U.S. Bureau of Standards of a number of commercial equipments for field-strength measurement at wavelengths within the range 200 to 500 m (frequencies 1 500 to 600 kc/s), showed that special precautions were necessary to ensure the attainment of an absolute accuracy within 20%. Apart from the introduction of the use of a shot-noise diode in place of thermal-agitation noise in the first tuned circuit, for adjusting the amplifier in a measuring set to a standard gain, there is no evidence from the published literature that any appreciable advance on the position described above has been made in the past ten years.What has been done, however, is to improve the technique of field-strength measurement at wavelengths below 10 m (frequencies above 30 Mc/s), and to extend the measuring technique to the shortest wavelengths now in common use for radio applications. These advances have taken place broadly along two main lines; (i) the separation of the calibrating unit from the field-strength measuring set, and its replacement by a method of producing a known field by radiation; and (ii) the replacement of current or voltage measurements which are used at frequencies below about 600 Mc/s, by a measurement of power at frequencies exceeding this value.With regard to the first, equipment has been developed at the National Physical Laboratory whereby radio field strengths at all wavelengths from about 30 m (10 Mc/s) to about 50 cm (600 Mc/s) can be produced and measured; and the methods are equally applicable to the measurement of continuous-wave and pulse-modulated radiation. The second line of development indicates that for wavelengths below about 50 cm (frequencies above about 600 Mc/s), it is more practicable to measure the power received in an aerial or waveguide system, of which the gain and directional receiving properties are known, than to adopt the more usual methods common at lower frequencies.At the present time, most of the types of equipment referred to above have been developed on an experimental basis for the use of research laboratories, and there is little commercially produced equipment available even for use at the lowest radio frequencies. While it is considered that field-strength measurement should nowadays be possible to a reliability of the order of 1 or 2 db (say 10 to 25%), the absence of adequate intercomparisons of the techniques on both a national and international basis naturally leads to some lack of confidence on the part of the user who may have important consequences dependent upon the results of such field-strength measurements.

DOI:10.1049/pi-3.1949.0007

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The meaning of the term “standard” in the field of electrical measurement is considered, and distinctions are drawn between definitive, derived, transfer and working standards. The recent change of units gives a reduction of the number of definitive standards. The various standards employed for radio frequency work afford good examples of the general ideas. The status and accuracy of the standards of capacitance, inductance and frequency are briefly reviewed.

DOI:10.1049/pi-3.1949.0008

出版商:IEE    

年代:1949

数据来源: IET

DOI:10.1049/pi-3.1949.0009

出版商:IEE    

年代:1949

数据来源: IET

摘要:

This paper is concerned with the problem of maintaining a low standing wave, over a wide frequency band, on the feeders of an aerial system. The problem involves a study of typical aerial impedance variations with frequency and of the possible devices which can be used to compensate these variations. The paper is illustrated by experimental impedance measurements on balanced twin feeders in the 500–600 Mc/s band. The results quoted give the authors considerable confidence in their methods of impedance measurement and compensation.

DOI:10.1049/pi-3.1949.0011

出版商:IEE    

年代:1949

数据来源: IET

DOI:10.1049/pi-3.1949.0012

出版商:IEE    

年代:1949

数据来源: IET