摘要:

Electronic communication needs of user organizations call for a ‘purpose orientated’ examination if they are to be properly understood and solutions derived. Identification of the hardware and implementation are generally well covered in the literature and the paper therefore concentrates on obtaining a better understanding of an organization and its communication environment so that a fully effective and efficient service can be given.

DOI:10.1049/ree.1980.0012

出版商:IERE    

年代:1980

数据来源: IET

摘要:

The signal acquisition time at the input to a charge transfer device is often much shorter than the minimum dock period for useful operation of the device. A feasibility study has been carried out to use this property to down-convert and detect directly, in one operation, a signal pattern carried by phase-shift keying a signal whose frequency is much greater than the maximum clock frequency of the charge transfer device.

DOI:10.1049/ree.1980.0013

出版商:IERE    

年代:1980

数据来源: IET

摘要:

A frequency-independent phase-shift network has been designed and constructed using field effect transistors as variable resistors. The operation of the system is shown to be similar to that of a phase lock loop with a self-generating v.c.o. Analysis of the system is given assuming linear operation. Phase difference outputs have been obtained in the frequency range 20–80 kHz. The phase error introduced in any set phase difference is ±2° in this frequency range. Theoretical predictions indicate this error could be reduced by an order of magnitude.

DOI:10.1049/ree.1980.0014

出版商:IERE    

年代:1980

数据来源: IET

摘要:

Experimentally-determined tuning characteristics are presented for a long cylindrical re-entrant cavity having dimensions similar to those used for Gunn oscillators and for studies on semiconductors. The results indicate the simultaneous existence of the dominant TEM and the fundamental TE modes of resonance. A perturbation technique is given for the identification of the modes. Theoretical calculations of the resonant frequencies using simple models are presented. Experimental values of theQ-factors of the resonator for both the modes of resonance are also given.

DOI:10.1049/ree.1980.0015

出版商:IERE    

年代:1980

数据来源: IET

摘要:

In television System I, the nominal bandwidth is 5.5 MHz but in most practical transmission systems the actual bandwidth is greater. There is a likelihood that video lowpass filters will be used in the future, for example in association with digital codecs, and it has been found that even when such filters have a passband of 5.5 MHz, critical signals such as colour bars and electronically generated captions exhibit ringing. To investigate the effect, the responses of existing PAL coder/decoders have been measured with and without a low-pass filter to define the transmission channel bandwidth. The filter currently proposed by the CCIR to shape the chrominance signal in the coder has a substantial response well above 5.5 MHz. In this situation it will have to be accepted that critical signals may be distorted at intermediate points along future transmission channels containing low-pass filters.

DOI:10.1049/ree.1980.0016

出版商:IERE    

年代:1980

数据来源: IET

摘要:

An unusual class of digital frequency synthesizers is presented capable of very high frequency-resolution. Construction may be made very simple. In typical applications the complexity of the hardware may be reduced by up to 50% compared with earlier approaches. A standard circuit is defined which may be used in a variety of applications, several of which have been outlined as illustrations of the flexibility of the technique.

DOI:10.1049/ree.1980.0017

出版商:IERE    

年代:1980

数据来源: IET

摘要:

This paper describes a technique for reconstructing a signal which has been sampled at a rate related to its short-term maximum frequency. The method described is based upon a theoretical simulation of active signal recovery filters containing periodically-operated switches. The cut-off frequency of such a filter is a function of the switching duty cycle. It is shown that the optimum filter is one with a sharp cut-off characteristic. The poor transient response usually associated with such filters is not a significant signal distortion factor.

DOI:10.1049/ree.1980.0018

出版商:IERE    

年代:1980

数据来源: IET