摘要:

Measurements of phase and amplitude have been carried out on signals on 37Mc/s received from a transmitter at Gibraltar. The receiving sites were at Slough and Castlemartin, which are each about 1740km from Gibraltar, and were equipped with pairs of aerials whose spacing could be varied from λ to 10λ. The results were not consistent with the idea that the forward-scattered signal was due to the combination of many randomly-phased radio waves. Frequently one signal appeared to be dominant, as might be expected if reflections from meteor trails formed an important part of the resultant signal. The calculation of an azimuth power distribution on the basis of phase measurements with different aerial spacings then becomes of uncertain validity. Some results obtained in this way are presented, but reliance is placed mainly on work with a small, fixed aerial spacing. This shows a marked diurnal variation of mean bearing; at Slough for most of the year it is on average 7°W of the Gibraltar bearing by night but 0°W by day. A comparison with observations at Castlemartin in Wales suggests that the scattering process is due almost entirely to meteor reflections by night but that during the day there is also present a component due to turbulent scattering which contributes rather more than half the total energy.

DOI:10.1049/pi-b-2.1961.0043

出版商:IEE    

年代:1961

数据来源: IET

摘要:

A study has been made of delayed signals reaching Slough from a transmitter at Gibraltar on 37Mc/s in the winter of 1956–57. The mean bearing of the first signal to arrive after that due to ionospheric forward-scatter was found to vary between 250° and 290° during the day; the spread of energy in bearing is also considered. It is shown that the radiation from the transmitter aerial must be stronger to the west than to the south. Results for the second delayed signal are also given. Round-the-world echoes were occasionally observed, but these did not arrive from the direction of the great circle containing Gibraltar and Slough.

DOI:10.1049/pi-b-2.1961.0044

出版商:IEE    

年代:1961

数据来源: IET

摘要:

The results of a number of short-term oversea measurements of the variation of received signal level with range from a 10Gc/s transmitter are presented. It is shown that the variation of signal level within the horizon was rarely that expected for propagation through an atmosphere having a uniform refractive-index gradient. Signal losses of from 5 to 30dB frequently occurred well within the horizon, these losses being recovered when the range between transmitter and receiver was sufficiently reduced. A well-defined interference pattern usually occurred in the region of reduced signal level. Some data on the variation of refractive index with height up to about 700ft above sea-level were gathered using a radio sonde and a captive balloon, but the detail was not sufficiently fine to enable a direct relationship to be established between signal losses within the horizon and the occurrence of irregularities in the refractive-index profile at low elevations.A direct relationship was found to exist between the signal level within the horizon and that propagated well beyond the horizon into the extra-diffraction region.

DOI:10.1049/pi-b-2.1961.0045

出版商:IEE    

年代:1961

数据来源: IET

摘要:

The paper gives an account of an experimental investigation of common- and immediately-adjacent-channel interference areas for mobile radio networks, based on a field-strength survey at 59Mc/s over flat and hilly country in north-west Germany. The variation of field strength with distance is shown to be in close accord with calculation. Particular attention has been paid to investigating the distribution of field strength at each distance, which is shown to approximate closely to log-normal. It is also established that the variance of these log-normal distributions may be considered to have a single value for each type of country, irrespective of range. Protection ratios acceptable for satisfactory operation are determined from experimental observation of common- and adjacent-channel interference. The derived data are used to determine probabilities of interference and are presented graphically for practical use.

DOI:10.1049/pi-b-2.1961.0046

出版商:IEE    

年代:1961

数据来源: IET

摘要:

The paper records the results of some tests made in the United States to compare results obtained with American, German and British radio-interference measuring sets when measuring the interference radiated by the ignition systems of motor vehicles. The tests show the close agreement between the results obtained when using the various national measuring sets and confirm the reliability and consistency of measuring equipment conforming to the specification of the International Committee on Radio Interference (C.I.S.P.R.). They also attempt to establish a relationship between the results of peak and quasi-peak measurements.The paper also tabulates and discusses the test conditions specified in the various countries and quotes the limits of ignition interference recommended or statutory in the countries concerned. A direct comparison of these limits, which is made possible by these measurements, suggests that the existing and proposed requirements of other countries are more onerous than those of the United Kingdom.

DOI:10.1049/pi-b-2.1961.0047

出版商:IEE    

年代:1961

数据来源: IET

摘要:

Band saving in television transmissions can be achieved by utilizing redundancies in single lines, between lines, between fields and between frames. The method of contour interpolation exploits the last two. It is based on the facts that (a) field and frame frequencies in conventional television transmission had to be chosen with a view to reducing flicker rather than for conveying more information, (b) the eye fixes mainly on contours which are usually the edges of objects, (c) these contours are usually smooth enough to allow interpolation over two line spacings, and (d) changes from one picture to the next come about mostly by the horizontal motion of objects which are sufficiently uniform to allow interpolation over at least two frame intervals. There is almost no loss in information or picture quality if the interlaced frame is suppressed in the transmission and reconstructed in the receiver by interpolation between the lines of the transmitted field, and there is not much loss if only one field in four is transmitted. In the method of contour interpolation the reconstructed edges are as sharp as the originals and appear in their correct positions, i.e. in the positions which they would occupy if the edges were straight in small sections, and if their motion were uniform for short times. The waveband gain can be estimated as 4 : 1 without appreciable deterioration in picture quality, and 8 : 1 if some deterioration is allowed in the case of rapid and vertical motions. In combination with other methods which utilize redundancies in single lines and which by themselves achieve a gain of 3 : 1, total compression ratios of 12 : 1 to 24 : 1 appear feasible.The principle was realized and tested in a photo-mechanical model working at low speeds. Electronic realizations are proposed and discussed.

DOI:10.1049/pi-b-2.1961.0049

出版商:IEE    

年代:1961

数据来源: IET

摘要:

When the Q-factor of a resonator is determined by using sinusoidal amplitude modulation and measuring the envelope phase shift, the presence of unwanted frequency or phase modulation may reduce the accuracy of the result. The envelope phase shift now depends on the ratio of the parasitic-modulation index to the amplitude-modulation index, and also on the phase angle between the two modulation components. If measurements are made with the carrier set as close as possible to the resonant frequency of the resonator, increased frequency stability is required. Alternatively, if advantage is taken of an approximation to exact tuning, which is given by setting the carrier so that the envelope phase shift is a maximum, a systematic error is introduced. If the ratio of the modulation indices or the phase relation between the modulation components is known, the systematic error may be determined and a correction can then be applied to the result. If either of two special phase relations can be set up between the modulation components, it appears that the parasitic modulation can be rendered innocuous; under these conditions as high an order of accuracy can be achieved as if pure amplitude modulation were used. This paper is supplementary to a previous paper which described a method for the measurement of very high Q-factors of electromagnetic resonators.

DOI:10.1049/pi-b-2.1961.0050

出版商:IEE    

年代:1961

数据来源: IET

摘要:

The specification and design of an amplifier required for precision audio-frequency measurements is discussed. Formulae are presented for the ‘ring of three’ feedback circuit and a detailed analysis is made of appropriate feedback theorems. A multi-gain amplifier which extends the voltage range of the electrostatic voltmeters, used at the N.P.L. as basic a.c./d.c. transfer instruments, is described. An increase in this range of up to 1000 times is provided and enables voltages between 60mV and 60 volts in the frequency range 30c/s–30kc/s to be measured to a few parts in 104.

DOI:10.1049/pi-b-2.1961.0051

出版商:IEE    

年代:1961

数据来源: IET

摘要:

Current transformers of existing design are found to have large high-frequency errors. The causes of these errors are examined and it is shown that they are due to the high values of leakage inductance, self-capacitance and concentrated inter-winding capacitance that result from the conventional multi-layer form of construction. Greatly improved performance can be obtained if the windings are arranged in uniformly-distributed single layers with a suitable thickness of insulation between them. Approximate formulae for calculating the various constants and errors of a transformer having single-layer windings are given, together with a design procedure for any specified limit of error over a wide band of frequencies. The practical aspects of the design are also discussed.Multi-ratio transformers in which all the ratios have virtually identical errors over a band of frequencies can be obtained by sub-dividing single-layer primary windings into sections, all of which are used by means of series-parallel connections for each ratio.Details are given of the design and performance of precision single-layer multi-ratio transformers rated from 5/5 to 400/5 amp. Their errors do not exceed 5 parts in 105in ratio and 0.3′ in phase over the frequency range 400c/s-10kc/s and are less than 2 parts in 104and 1′ over the range 50c/s-30kc/s.

DOI:10.1049/pi-b-2.1961.0052

出版商:IEE    

年代:1961

数据来源: IET

摘要:

When standard current transformers are tested at high audio frequencies the errors and uncertainties in the measurements are liable to be great owing to the effects of stray magnetic fields on the large unshielded resistors which of necessity have to be used. The sources of stray fields are examined and means are suggested for substantially reducing them. It is shown that the 4-terminal resistance standards used in current-transformer testing bridges are very frequency-dependent and present techniques limit the accuracy of measurement at 20 kc/s to 2 parts in 104in ratio and 0.8′ in phase.New techniques are described by which the errors and uncertainties can be reduced to give an accuracy of 5 parts in 105and 0.1′ at 20 kc/s.

DOI:10.1049/pi-b-2.1961.0053

出版商:IEE    

年代:1961

数据来源: IET