DOI:10.1049/ree.1981.0078

出版商:IERE    

年代:1981

数据来源: IET

摘要:

The performance of surface survillence radars is complicated by temporal changes of propagation loss, sea and rain clutter and target behaviour. This paper presents short and medium-term statistics using a real time pulse-to-pulse digital analyser operated in conjunction with high dynamic range logarithmic receivers fed from an experimental dual antenna coastal radar.Previous performance predictions18made for equipments operating in true diversity, themselves supported by extensive trials24over half minute intervals of observation, are now augmented with true pulse-by-pulse measurements on targets obtained in each common beam dwell time of a true composite dual channel experimental radar.Short-term measurements on sea and rain clutter show that predictions based on average or mean values of sea and rain clutter are a poor guide to true short term variations, but become more accurate over longer periods as found by others.25Illustrations from p.p.i.s are given of both targets and clutter from the experimental radar, showing the effects of optimum and non-optimum video processing of the output from the two channels and results from a captive target balloon at selected elevations are included.

DOI:10.1049/ree.1981.0079

出版商:IERE    

年代:1981

数据来源: IET

摘要:

In place of Coulomb's Law,F=q1q2/4φε0r2,the formulaF= (q1q2/4φε0r2)√[1+v2/c2]is proposed, wherevis the velocity of one charge relative to the other. Using this velocity-dependent force law, it is shown how Ampere's law can be derived; Maxwell's equations can then be obtained, and their limitations can be discussed. The concept of field is shown to be valid only in the limiting case of vanishing velocities, so that Maxwell's theory is approximately valid only when any motion is slow and any rate of change of field is small. When these conditions do not hold, Maxwell's theory is invalid, but the velocity-dependent force law can be used. The motions of charged particles in electric and magnetic fields are discussed. Anomalous apparent decay times of fast mesons are attributed not to time dilation but to speeds greatly exceedingc. Some anomaly remains, and it is suggested that new experimental observations are necessary to resolve this.

DOI:10.1049/ree.1981.0080

出版商:IERE    

年代:1981

数据来源: IET

摘要:

Given the requirement for a line-of-sight link operating over a sea path and having established the clearance at the horizon over the appropriate range ofk-values using standard procedure, a method is derived for determining the optimum spacing for worst case conditions between receiving antennas where dual space diversity is employed to reduce 2-path fading. The means of calculating the minimum received signal, i.e. the deepest fade possible with destructive interference in the 2-path mode, is also included; as a check on performance if the optimum spacing cannot be realized or where the optimum value is used and the worst case conditions assumed in this determination do not apply in practice.Programs for these calculations are included which run on TI58 or TI59 pocket calculators. A third program for the calculation of Fresnel zone numbers (cubic equation solution) is included. The method is valid for any frequency band in which line-of-sight criteria apply and 2-path propagation occurs.Although consideration of the probability of occurrence of any particular propagation mode lies outside the scope of this paper, it is found that the correct 2-path diversity spacing also provides substantial protection in other adverse propagation circumstances.

DOI:10.1049/ree.1981.0082

出版商:IERE    

年代:1981

数据来源: IET

摘要:

Adaptive transform coding using the discrete cosine transform for monochrome pictures is considered. Selecting which coefficients to transmit and with how many bits involves an estimate of each coefficient's energy. Dividing the image of 256 lines, 256 pels/line into blocks of 16 × 16 pels, we consider two estimation methods for the bit allocation process. One method involves the mean energy of each coefficient, while the other is an approximation to this method, called Energy Distribution Logarithmic Model, that drastically reduces the amount of side information that must be transmitted. To this we add an adaptive coefficient selection procedure based on the energy of three neighbouring coefficients. Performing the experiments by means of computer simulation we were able to achieve an average of 0.55 bits/pel for a recovered image having a mean square error of 0.1%.

DOI:10.1049/ree.1981.0083

出版商:IERE    

年代:1981

数据来源: IET

摘要:

The paper presents the general theory of automatic gain control (a.g.c). It includes discussions on loop gain, regulation and the relation between loop parameters and output level stability. An equivalent circuit is derived which is used in the study of dynamic behaviour. The work is extended to cover sampled data a.g.c. systems and design guidelines are derived for a variety of situations.

DOI:10.1049/ree.1981.0084

出版商:IERE    

年代:1981

数据来源: IET

摘要:

Measurements of the amplitude of the detected envelope of man-made noise have been made at a frequency near 80 MHz, and the results presented in the form of amplitude probability distribution curves. The major contributing sources are the ignition systems of vehicles and measurement locations such as business areas, arterial roads, and suburban areas have been chosen to give a variety of conditions. Although traffic density is the major parameter that has to be taken into account, the pattern of traffic flow is also a contributing factor.

DOI:10.1049/ree.1981.0085

出版商:IERE    

年代:1981

数据来源: IET

DOI:10.1049/ree.1981.0086

出版商:IERE    

年代:1981

数据来源: IET

DOI:10.1049/ree.1981.0087

出版商:IERE    

年代:1981

数据来源: IET