摘要:

Explicit solutions are presented for the capacitance arising from the electric field distortion caused by one of two step discontinuities bounding a short length of increased or decreased conductor spacing in parallel-plane transmission lines. Values are tabulated of a proximity factor which may be multiplied by the capacitance resulting from the field distortion associated with an isolated step to account for the presence of a second, similar step.

DOI:10.1049/piee.1976.0160

出版商:IEE    

年代:1976

数据来源: IET

摘要:

This paper presents a simple technique for eliminating the need for a post-delay line low-pass filter in a low-frequency correlator. A bucket-brigade delay line is used in a dual capacity giving the correlator a wider application.

DOI:10.1049/piee.1976.0161

出版商:IEE    

年代:1976

数据来源: IET

摘要:

A laboratory model synchroniser for the earth station of a switching satellite system is described and its performance is compared with theoretical predictions. The results included in the paper confirm the pertinent theory through measurements made on the model operating in its coarse-search mode, fine-search mode and tracking mode.

DOI:10.1049/piee.1976.0162

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The paper presents an analysis of the information properties of delta-coded speech with channel-encoding applications. Predictive coding techniques for reducing the entropy of the average distribution of the signal elements are described, and evaluated by comparison with computations of the relative entropy of Markov process approximations to the message-generating process, for orders up to 9. The optimal digital fixed-structure predictors are established for orders up to 7, and the optimal group codes are established for block lengths of 2 to 6 elements. The redundancy is shown to be typically about one half, and a predictor success probability of 0.9 is attainable with a practical 6th-order discrete structure. The entropies of the sequences, which are generated by modulo-2 addition of the predictions and source elements, are found to be much closer to the process entropies than are the corresponding performance characteristics for group encoding. In order to achieve message compression, for encoding the predictor error sequence, 5-element group encoding (attaining a compression factor of 0.5 with a 300-word buffer) is found to be superior to run-length encodings. The combination transformation is much more efficient than direct exact coding of blocks of source elements.

DOI:10.1049/piee.1976.0163

出版商:IEE    

年代:1976

数据来源: IET

摘要:

A signal detection method for delta-coded speech is presented which exploits the redundancy of the source to reduce the error rate owing to additive Gaussian noise in the channel. The method implements a Bayes strategy with dual decision boundaries selected by a 6th-order digital predictor. Fixed decision boundary pairs, appropriate for a wide range of input signal/noise ratio, are established. This easily implemented technique is shown to give an error-rate reduction of about 40% in coherent antipodal and coherent and noncoherent orthogonal communication.

DOI:10.1049/piee.1976.0164

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The study considers the effect of error rate, block length, transmission delay, and error-recovery mechanism on the efficiency of the communications channel in computer-computer communications. The systems investigated are full-duplex communications with unlimited and limited buffering, and half-duplex communications. Both random and burst errors are considered. For all cases, over a significant range of parameters, closed-form expressions for the optimum block length, and the corresponding efficiency are obtained. For random errors the optimum data-block length is found to be proportional to √(a/k), and the maximum efficiency a function ofka, whereais the message overhead andkis the error rate. The burst error results are similar.

DOI:10.1049/piee.1976.0165

出版商:IEE    

年代:1976

数据来源: IET

摘要:

This paper describes a simple circuit for improving the pull-in capability and capture time performance of second-order phase-locked loops without degrading the noise rejection properties of the loop. Experimental results are presented for several values of loop damping factor and natural frequency.

DOI:10.1049/piee.1976.0166

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The results of a site-diversity experiment at 37 GHz with sun-tracking radiometers at three sites 10.3, 12.7 and 18 km apart, near Slough, UK, are described in relation to Earth-space communication links. Data for observation periods of 16, 8 and 9 months from the three pairs of sites are presented in the form of cumulative distributions and of diversity advantage as a function of attenuation, together with histograms of the number and duration of individual fades exceeding 10 dB. The largest diversity advantage was found for the 18 km spacing and the least advantage was with the 12.7 km spacing for which the sites were aligned approximately perpendicularly to the direction of movement of prevailing storms. A method is given for predicting diversity characteristics at one frequency from measurements made at another, based on two sets of measurements made at Slough; one made concurrently at 19 and 37 GHz, the other made concurrently at 37 and 71 GHz.

DOI:10.1049/piee.1976.0167

出版商:IEE    

年代:1976

数据来源: IET

摘要:

This paper describes the design, fabrication and assessment of twelve s.a.w. matched filters on ST-quartz used to demodulate data in a four-level f.s.k. system. The system uses four frequencies separated by 250 kHz around 70 MHz, and the pulse length (4, 12, or 36 μs) may be selected according to the input signal/noise ratio to ensure reliable detection of the matched filter outputs. A 12 μs transducer made up of 4 μs and 8 μs sections was used as the basic design unit. This provided the 4 μs and 12 μs devices, and piecing three 12 μs sections on the same substrate gave us the 36 μs devices. We have used thinned output transducers and quarter-wave cancellers to reduce reflections. Individual frequency responses of each of the twelve filters showed relevant nulls better than 35 dB. When all four frequency responses of a filter bankwere superimposed, the orthogonal channel rejection was 25 dB in the worst case, which is adequate for error-rateperformance within 1 dB of theory. Computer simulation showed close agreement with measured responses. The model includes taper, random phase errors incurred at the artwork cutting stage, electromagnetic delay and, in the case of 36 μs devices, piecing errors and curvature of the 15 cm substrate.

DOI:10.1049/piee.1976.0168

出版商:IEE    

年代:1976

数据来源: IET

摘要:

In a previous paper it was demonstrated that considerable reduction in the harmonic content of a circulating current cycloconvertor could be obtained by regularly sampling the reference waveforms which control the firing of the thyristors. The paper describes how this sampling process also allows the reference waves, needed for a cycloconvertor with a multiphase output, to be produced from a single sinusoidal waveform. The difficulty of producing a polyphase set of sinusoidal reference waveforms balanced in amplitude and equally displaced in phase is thus eliminated. This is of particular advantage when the amplitude andy frequency of the reference waveforms are to be voltage controlled. The paper demonstrate show this principle may be extended to the general design of multiphase signal generators. Methods are described for determining the frequency, the phase displacement and the phase sequence of sampled signals. The paper concludes that the introduction of regular sampling in cycloconvertors permits the use of a high-frequency reference waveform in the place of low-frequency waveforms and the use of a single-phase wave generator instead of the usual 3-phase waveform generator with a consequent saving in the cost of control equipment.

DOI:10.1049/piee.1976.0170

出版商:IEE    

年代:1976

数据来源: IET