摘要:

The need for control of interference to broadcast reception together with the realization that differing controls could constitute trade barriers led to the establishment in 1934 of the CISPR (International Special Committee on Radio Interference). Agreement on basic measuring techniques, instrumentation design and suppression methods was achieved quite rapidly. Agreement on actual limits took longer.

DOI:10.1049/jiere.1987.0091

出版商:IERE    

年代:1987

数据来源: IET

摘要:

The accumulation and tolerance of timing jitter in digital networks is analysed for transmission links containing regenerators as well as dejitterizers and/or multiplexer—demultiplexer pairs, and for timing circuits employing phase-locked-loops. Both systematic pattern-dependent jitter and waiting-time jitter are taken into account. It is shown that, under practical circumstances, the total accumulated jitter can be adequately described by some simple equations and measurement data confirm these equations. An experimental relation between peak-peak jitter values over a long period and those over a short period is presented. The results of the analysis have led to the conclusion that the internationally recommended maximum permissible peak-peak jitter values at digital interfaces will never be reached in the Dutch digital network.

DOI:10.1049/jiere.1987.0092

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Many approaches have been suggested in recent years for functional testing of LSI/VLSI chips. Most of these techniques are reviewed in this paper and the advantages and disadvantages of each technique are discussed. Finally, some suggestions for future work in functional testing are made.

DOI:10.1049/jiere.1987.0093

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Conventional tracking filters using feedback control encounter a hang-up problem when fast acquisition is required in high-speed TDMA systems. This paper introduces a feedforward tracking filter (FTF) which solves the hang-up problem. Using two identical bandpass filters (BPF5) and feedforward control to compensate both phase and frequency variations, this FTF provides fast acquisition and unconditional stability. Different BPF configurations used in the FTF scheme are evaluated and it is found that, for the same noise bandwidth of the BPF, the FTF using two identical double-tuned BPFs provides the best performance. The fast acquisition of the FTF is not degraded by the inter-burst-interference encountered in TDMA applications. The effects of misaligned BPFs on the tracking performance are studied analytically and experimentally.

DOI:10.1049/jiere.1987.0094

出版商:IERE    

年代:1987

数据来源: IET

摘要:

The performance of a Feedforward Tracking Filter (FTF) in the presence of white additive Gaussian noise is analysed. By studying the spectral properties and input-output signal-to-noise ratio (SNR), it is observed that the output of the nonlinear bandpass model of the FTF contains a mixture of signal and noise cross-modulation products. Due to the nonlinear effect, the FTF achieves tracking abilities at the expense of SNR. In addition, the probability density function of the phase error is evaluated. Finally, experimental results to verify the analysis and an application of the FTF to a fast carrier recovery system are presented.

DOI:10.1049/jiere.1987.0095

出版商:IERE    

年代:1987

数据来源: IET

摘要:

A technique is presented for modelling lattice-work metallic structures with dimensions in the resonant region of the illuminating radiation. A simple model for the scattering from a single strut is used as the building block for a complete lattice-work structure, giving the spatial distribution of the scattering, and a scale model is used to validate the amplitude normalization for one particular case.The application of the technique to a 45 m tall vent stack is described, where the vent stack was to be constructed in the paths of microwave data and voice links. Measurements at the site in Norfolk after construction of the vent stack are described and clearly demonstrate the effectiveness of the model.

DOI:10.1049/jiere.1987.0096

出版商:IERE    

年代:1987

数据来源: IET

摘要:

The design of feedback controllers for uncertain nonlinear plants is greatly simplified if the vagaries of the nonlinear behaviour of the plant can be accounted for by the variation of the parameters of an equivalent linear model of the plant, whereby the latter is able to predict the span of all possible responses generated by the plant. This change of philosophy permits the application of all existing linear control theory. In particular, familiar frequency-domain techniques may be employed in the design of controllers to constrain the operation of the feedback system to within toleranced bounds enveloping an acceptable time response.Thus, a necessary stage in the application of such sensitivity concepts to system design, where the plant may be both nonlinear and uncertain, is the determination of the complete range of equivalent linear models to represent the plant. This requires the identification of an appropriate model structure and the estimation of the range of variation of its parameters.Two methods, which previously have been employed in the time and frequency-domain synthesis of signals, are compared in this new role with a modification of the standard recursive least-squares routine which allows a direct estimation of the Laplacian system function. It is seen that, in general and not unexpectedly, the equivalent linear model may have to be of comparatively high order and, for certain regimes of operation, may call for ‘operationally-localized’ right-half plane poles. However, these attributes are of no disadvantage when the model is to be used for sensitivity reduction based upon the synthesis of the loop frequency response.

DOI:10.1049/jiere.1987.0097

出版商:IERE    

年代:1987

数据来源: IET

摘要:

A simple method is introduced by which, during measurements of noise figure and gain, the output reflection coefficient of the device under test can be adjusted to some constant value without the use of a network analyser, thereby keeping the noise figure of the noise measurement system constant. This removes an important source of error in noise figure and noise parameter measurements.A circulator and tuning network (e.g. a three-stub tuner) are used, but there is no need for the circulator to be tuned for perfect circulation. In an experimental test to verify the accuracy of the method, excess noise temperatures and available gains of a two-port were measured for a wide range of values of the complex reflection coefficient of the noise source and compared against values calculated from the measured scattering parameters of the same two-port.

DOI:10.1049/jiere.1987.0098

出版商:IERE    

年代:1987

数据来源: IET