DOI:10.1049/ree.1982.0031

出版商:IERE    

年代:1982

数据来源: IET

摘要:

This paper considers the nature of the speech mechanism, and the effects on the speech spectrum of a high pressure helium-air environment. A comparison is made between the characteristics of speech distortions in a helium-air mixture and certain well-known characteristics of speech in normal air which give rise to similar effects.The criteria for good intelligibility are related to the performance of various helium speech unscrambling techniques which have been used. These unscrambling techniques are classified here into two main categories: those essentially using signal processing in the frequency domain and those using signal processing in the time domain. Consideration is also given towaveform coding techniques which involve a combination of both of these classes of signal processing.The ability of these categories to incorporate the various features required for good intelligibility in unscrambling helium speech is discussed, in order to highlight the potential importance of frequency domain approaches to future unscrambling developments.

DOI:10.1049/ree.1982.0032

出版商:IERE    

年代:1982

数据来源: IET

摘要:

Dynamic logic circuit technology has been used widely to implement large-scale integrated (l.s.i.) circuits using metal-oxide-silicon field effect transistors (m.o.s.f.e.t). One of the factors which determines the overall dimensions of a custom-designed random logic l.s.i. circuit is the number of interconnection tracks as they occupy a large part of the chip between functional modules. This paper describes a multiplexing technique, which allows a reduction in the number of interconnection tracks between modules in l.s.i. circuits implemented using the four-phase dynamic logic technology of the major—minor configuration. It is shown that the operating speed or performance of the circuit is not affected by this technique.

DOI:10.1049/ree.1982.0033

出版商:IERE    

年代:1982

数据来源: IET

摘要:

This paper briefly describes four areas of work involved in trying to establish the reliability and limitations of thickfilm materials. One of the most widely used resistor systems, Du Pont 1400, has been extensively examined and long-life stability predictions are made. The possibility of replacing gold conductors with lower cost silver alloys depends critically upon controlling or eliminating silver migration, and the conditions under which migration occurs are described. The replacement of alumina substrates with alternative materials such as enamel steel, polymer board or glass is also reported, and the behaviour of the thick film materials has been found to be generally inferior to those on alumina. The Du Pont CMS nitrogenfireable resistor, conductor and dielectric system has been evaluated and the properties found to be comparable with air-fireable systems.

DOI:10.1049/ree.1982.0034

出版商:IERE    

年代:1982

数据来源: IET

摘要:

A proposal is presented for a system for the encryption of the signal resulting from the time division multiplexing ofNchannels carrying digital voice signals. The channel synchronization principle is such that no extra sync-signal is transmitted but synchronization is extracted from the information signal. Furthermore, it provides a first echelon encryption of the signal because there is a continuous and random shift of the position of each channel in time. The main encryption of the signal is done on a bit-by-bit basis, by modulo-2 adding to the signal a sequence that is derived from a non-linear combination of several past bits of the encrypted signal. This is achieved by using an e.p.r.o.m. in conjunction with a r.a.m. In an alternative system, this sequence is derived from a pseudo-random sequence generator that is also controlled by some past bits of the encrypted signal. In both cases synchronization and encryption are based on the transmitted signal itself.

DOI:10.1049/ree.1982.0035

出版商:IERE    

年代:1982

数据来源: IET

摘要:

Polar orbiting satellites, equipped with random access data collection and position fixing systems, have made practicable long-term remote oceanographic and meteorological observations by means of instrumented drifting buoys fitted with u.h.f. telemetry transmitters. The paper discusses the performance of nine buoys, deployed by the Institute of Oceanographic Sciences as part of the FGGE Southern Hemisphere Drifting Buoy Network, and presents a small fraction of the considerable data set acquired to date. The requirements for further development of certain sensors and components of buoy hardware are brought out as a result of the experience with these buoys.

DOI:10.1049/ree.1982.0036

出版商:IERE    

年代:1982

数据来源: IET

摘要:

Spread-spectrum communication techniques use a common wideband channel to obtain subscriber accessing in secure, jam resistant links. Phase shift keying (p.s.k.) and frequency hopping (f.h.) under the control of a pseudo-noise (p.n.) code are favoured signal waveforms. The paper reviews the performance of surface acoustic wave and charge-coupled device fixed coded and electronically programmable analogue matched filters for the detection of short (13 to 1023 chip) 1 kHz to 20 MHz chip (clock) rate p.n.-p.s.k. coded signals. The extension of these matched filters to accommodate the longer codes 10000 chips) and integration times (several milliseconds) used in current spread-spectrum systems is reviewed, and their importance in reducing synchronization acquisition is highlighted.Surface acoustic wave device approaches to synthesize and detect the alternative f.h. spread-spectrum waveforms are also discussed. The realizations of digitally-controlled coherent frequency synthesizers using s.a.w. chirp filters and bandpass filterbanks are highlighted. Finally the paper identifies the problem in many spread-spectrum systems, where the input-signal-to-interference ratio is so low that code matched filtering alone is not sufficient to detect the transmitted data, and it investigates the use of adaptive signal processing techniques for further suppression of wide and narrowband interference.

DOI:10.1049/ree.1982.0037

出版商:IERE    

年代:1982

数据来源: IET