DOI:10.1049/pi-b-2.1960.0135

出版商:IEE    

年代:1960

数据来源: IET

摘要:

Thermistors are components of comparatively recent development, although the phenomenon of conduction in metallic salts was recorded by Faraday over a century ago.The paper, in a broad survey of the subject, describes the theory of their operation, explains why they, in common with other semiconductor devices, possess a negative temperature coefficient of resistance and develops the expressions which govern their parameters.Methods of manufacture of the various forms of thermistor are outlined in general terms, and numerous applications of the device are described and discussed. Guidance is given on the approach to circuit problems, and the possibilities of exploiting some of the device's interesting and unusual properties are indicated. The point is made that the thermistor can now be used in many fields as an adequate alternative to components of more specialized application.

DOI:10.1049/pi-b-2.1960.0136

出版商:IEE    

年代:1960

数据来源: IET

DOI:10.1049/pi-b-2.1960.0139

出版商:IEE    

年代:1960

数据来源: IET

摘要:

In f.m. reception, the delayed signals caused by multi-path propagation result in unwanted amplitude and phase modulation of the primary signal, and consequent distortion of the programme output of the receiver. The paper describes the results of tests which were carried out in simulated multi-path conditions to determine the importance of the parameters of both the received signal and the receiver in influencing the subjective annoyance caused by the distortion.With a well-designed receiver, the distortion of piano music is ‘slightly disturbing’ when a single delayed signal is present having an equivalent path difference of 8 km and an amplitude of 35% relative to the primary signal. For a path difference of 29 km, however, the permissible relative amplitude is only 6% for the same subjective annoyance. Under the same conditions the distortion of speech is imperceptible. In comparison, receivers providing inadequate suppression of the unwanted amplitude modulation are much more susceptible to the distortion.The use of pre-and de-emphasis appreciably reduces the distortion, being equivalent to a reduction of about 8 dB in the amplitude of the delayed signal when the path difference is about 16 km. Similarly, the distortion is less noticeable when the loudspeaker has a poor response at high audio frequencies.The mechanism of multi-path distortion is discussed, and the harmonic spectra of the distortion shown for particular conditions.

DOI:10.1049/pi-b-2.1960.0140

出版商:IEE    

年代:1960

数据来源: IET

摘要:

A marked variation occurs over the sunspot cycle in the discrepancies between predicted F2-4000km m.u.f. and the observed times of fade-in and fade-out on an 18.4Mc/s Bombay-London circuit. This is particularly marked in summer and is attributed to the influence of the sporadic-E layer, although there is no marked sunspot-cycle effect attributed to this layer.Any assessment of the accuracy of predictions analysed on the assumption of F-layer propagation must be considered in relation to the phase of the sunspot cycle to which it refers

DOI:10.1049/pi-b-2.1960.0143

出版商:IEE    

年代:1960

数据来源: IET

DOI:10.1049/pi-b-2.1960.0144

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The directional aerial described employs a corner reflector excited by a four-tier slotted cylinder. It was used during a series of test transmissions in Band V (610–960 Mc/s) which required an aerial capable of withstanding severe climatic conditions for long periods without attention.A design suitable for operation at 900Mc/s is described; the measured results include admittance characteristics and radiation patterns in the horizontal and principal vertical planes.

DOI:10.1049/pi-b-2.1960.0145

出版商:IEE    

年代:1960

数据来源: IET

摘要:

After an initial discussion of short-term correlation functions the design and performance of an auto-and cross-correlator using Halleffect multipliers are described. It is shown that these devices are well suited to act as the multiplying elements and as modulators in associated circuits, provided that one of the time functions to be multiplied has a narrow bandwidth. Examples of measured auto-and crosscorrelation functions are given for sine waves and noise and for the control signals of a vocoder, from which interesting conclusions can be drawn about the redundancy of vocoder signals.

DOI:10.1049/pi-b-2.1960.0146

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The paper describes an investigation of some problems of sound diffusion in rooms, with particular reference to small sound and television studios. The experimental work shows that it is possible to measure the degree of diffusion in a room by fairly simple practical techniques. Quantities based on the frequency variation of reverberation time and double reverberation decay constants are the most promising for use in small broadcasting studios.It is also shown that uniform distribution of absorption can be as effective as other means of attaining conditions of good diffusion. Rectangular diffusers are particularly effective in improving conditions where the distribution of absorption is poor.

DOI:10.1049/pi-b-2.1960.0147

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The paper describes a transistor chopper-type d.c. amplifier which is intended for use in the field of process measurement and control. It has a voltage drift below ±10 μV and a current drift below ±4×10−9amp.The forward gain in the steady state is about 10kV/μA and 15 volts/μV, and, in consequence, the full output swing of 0 to 5 volts is provided by an input signal little greater than the drift. The application of sufficient overall negative d.c. feedback therefore enables input signals of 0–10 mV or 0–4 μA to provide full output with an accuracy of ±0.1%.The low drift is obtained by operating the transistor chopper 200 c/s, stabilizing its temperature within ±2°C, and providing suitably stable waveforms to drive the transistor and compensate for its voltage offset.The a.c. gain prior to the demodulator is only 50 volts/μA, the remaining voltage gain, of about 200, being provided by a low-drift d.c. amplifier which is connected as a feedback integrator and used smooth the demodulated output. This arrangement enables the system to handle, with a minimum of saturation, the large error signals which occur during a rebalancing operation, and thus maintain a fast response to large changes of input signal.The system is first analysed in general terms, and expressions are derived which describe its performance and act as a guide to the design of this type of amplifier.

DOI:10.1049/pi-b-2.1960.0148

出版商:IEE    

年代:1960

数据来源: IET