摘要:

The data available for calculating the ground-ray field are summarized and used as a basis for estimating the maximum range of communication for any given practical conditions. Particular attention is given to low-power (e.g. portable) transmitters with short aerials, and to the way in which the range of communication varies with wavelength and with the aerial used.Sky-wave communication is not treated, since it cannot normally be relied upon with the very low radiated powers (1 watt or less) primarily considered in the paper. Centimetre waves also are not covered: the range is here principally dependent upon the permissible aerial directivity, and many of the problems involved are of a some what different nature from those dealt with in the paper.Simplified field-strength formulae of general application are derived from the work of Burrows2and Norton.3Curves are given for the distance at which the field from a 1-watt transmitter falls to a given value for wavelengths from 0.5 m to 2000 m and aerial heights up to 15000 ft.An analysis of the ratio of power radiated to total power available gives the reduction in field from the transmitter when short aerials are used. The minimum field required at the receiver for intelligible communication is considered, and curves are then drawn for the range of communication.Practical rules are given for estimating ground-ray range for low-power sets.

DOI:10.1049/ji-3-2.1948.0107

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper deals with the design of direction-finding aerial systems to cover the whole of the h.f. band, to work on the ground wave and to meet the conditions peculiar to H.M. ships. The special problems encountered are intimately connected with the siting of the d.f. aerial. The aerial must be fitted to the top of a mast, and often at a considerable distance from the receiving compartment.The most satisfactory design of d.f. aerial to meet these conditions consists of two fixed crossed loops with an incorporated sense aerial, and a network for injecting test signals into the d.f. and sense-aerial circuits. The aerial system must be connected to the receiving apparatus by means of transmission lines which may be of considerable length.The paper describes the special problems experienced in achieving satisfactory performance in sensitivity, bearing accuracy and resolution of sense ambiguity, the compromises in design that have to be adopted and the performance figures obtained.

DOI:10.1049/ji-3-2.1948.0109

出版商:IEE    

年代:1948

数据来源: IET

摘要:

One of the major limitations to the efficacy of radar is the presence of responses from land, sea or rain-storms in the vicinity of a target, such responses being generally known as “clutter.” If the clutter is of amplitude greater than the target-echo, detection of the echo is very difficult; in many cases, however, the clutter is of amplitude smaller than the target-echo, but the latter is lost owing to saturation of the receiver or display equipment by the clutter. It is shown, both theoretically and practically, that such loss can be prevented in the cases of sea and rain clutter by the use of a receiver, the amplification characteristic of which is such that the amplitude of an output signal is proportional to the logarithm of the amplitude of the corresponding input signal; in the case of land clutter, loss is not necessarily prevented, but the probability of such loss is reduced.A logarithmic receiver compresses input signals of any strength less than 100 db above the mean noise power, into output signals of voltage less than four times the output-noise deviation voltage, with negligible change in the detectability of small signals compared with the use of a linear receiver. In addition, with such a receiver, the difference in voltage of two output signals depends only on the ratio of the corresponding input signals, and not on their absolute amplitudes. These properties make a logarithmic receiver superior to a linear receiver for a number of subsidiary applications, some examples being given in the paper.

DOI:10.1049/ji-3-2.1948.0112

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Resonant cavities have been used to measure the frequency and check the performance of radar transmitters. The object of this paper is to describe the factors influencing the design of such cavities to cover frequency bands near 3000 Mc/s, and to estimate their accuracy in the measurement of both the mean frequency of the transmitter output and its spectral distribution about the mean. The principles described are of general application to the design and use of cavity wavemeters of high discrimination.

DOI:10.1049/ji-3-2.1948.0117

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Theoretical formulae are found for the reflection from flat sheets and angle reflectors. The reflection diagram from a flat sheet is the same as the transmission polar diagram of an aperture of double the dimensions of the sheet. A small deviation from flatness considerably alters the diagram, a sag of half a wavelength at the centre producing a zero where there would otherwise have been a maximum. The right-angled corner reflector is also investigated, and the broad reflection diagram expected from geometrical optics is found. The effect of a small departure of the included angle from a right angle is also discussed.

DOI:10.1049/ji-3-2.1948.0118

出版商:IEE    

年代:1948

数据来源: IET