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首页> 外文期刊>Electrical Engineers - Part IIIA: Radiocommunication, Journal of the Institution of >The fading machine, and its use for the investigation of the effects of frequency-selective fading
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The fading machine, and its use for the investigation of the effects of frequency-selective fading

机译：衰落机及其在研究频率选择衰落的影响中的用途

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摘要

The function of the fading machine is to simulate the frequency-selective fading which is characteristic of long-distance short-wave radio channels. Fading of this type is usually due to interference between waves which have traversed multiple paths between sender and receiver, and its effect is often to produce distortion of the modulation of radio waves. Many radio transmission systems have been devised with the object of minimizing the effects of selective fading; the fading machine enables different systems to be compared in the laboratory under precisely controlled fading conditions. The equipment described in the paper incorporates three transmission paths, the group time-delay differences between which may be varied in steps from 0 to 2 milliseconds. The phase differences between the paths may be varied manually (????????static???????? fading) or continuously (????????dynamic???????? fading), with fading rates ranging from 0.1 to 10 fades per second. Random noise, either fading or non-fading, may be included so as to synthesize a complete short-wave radio channel. The fading machine may also be used to simulate diversity reception obtained by spaced aerials. Examples are given of the use of the equipment to assess the merits of double-sideband, single-sideband and frequency-modulated transmission systems with telephony or telegraphy modulation, under conditions of severe selective fading and high noise level.
机译：衰落机的功能是模拟长距离短波无线电信道所特有的选频衰落。这种类型的衰落通常是由于波之间的干扰造成的，该波在发送者和接收者之间经过了多条路径，并且其效果通常是使无线电波的调制失真。为了使选择性衰落的影响最小化，已经设计了许多无线电传输系统。衰落机可以在精确控制的衰落条件下在实验室中比较不同的系统。本文描述的设备包含三个传输路径，它们之间的组时延差可以在0到2毫秒的范围内逐步变化。路径之间的相位差可以手动更改（静态更改）或连续更改（动态更改）。淡入淡出），淡入度范围为每秒0.1到10次淡入。可以包括衰落或非衰落的随机噪声，以便合成完整的短波无线电信道。衰落机还可以用于模拟由间隔开的天线获得的分集接收。举例说明了在严重的选择性衰落和高噪声条件下，使用该设备评估带有电话或电报调制的双边带，单边带和调频传输系统的优点。

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