A Theoretical and Experimental Investigation of Tuned-Circuit Distortion in Frequency-Modulation Systems

D. L. Jaffe
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引用次数: 9

Abstract

The problem of distortion introduced into the modulation intelligence by tuned circuits is considered both theoretically and experimentally. Complex equations result when the effect of the intelligence modulation is considered. These equations, while not readily amenable to Fourier analysis, disclose that the distortion parameters are ΔW/BW and λ/BW where, ΔW/2π = peak-frequency swing λ/2π = modulation frequency BW = bandwidth in kilocycles measured at 3 decibels down. Double-tuned circuits critically coupled. If the effect of the modulation frequency is neglected, the equations resulting from a theoretical analysis are somewhat simplified and the distortion due to single- and double-tuned circuits can be formulated. Close agreement between calculated and measured distortion was obtained up to approximately a 5000-cycle-per-second modulation frequency. At this frequency the departure of the observed from calculated values was quite noticeable. Theoretical maximum-distortion limits for the single- and double-tuned circuits are derived. For the single-tuned circuit the theoretical maximum distortion is Dnmax (single-tuned circuit) = 2λ/ΔW·100. For the double-tuned circuit it is Dnmax (double-tuned circuit) = 4λ/ΔW·100 A conservative design figure relating bandwidth to frequency swing in order to insure distortion-free transmission to 15,000 cycles per second was experimentally found to be, ΔW/BW = 1/4.
调频系统中调谐电路畸变的理论与实验研究
从理论上和实验上考虑了调谐电路在调制智能中引入的失真问题。当考虑智能调制的影响时,会产生复杂的方程。这些方程虽然不容易适用于傅立叶分析,但揭示了失真参数为ΔW/BW和λ/BW,其中ΔW/2π =峰值频率摆动λ/2π =调制频率BW =带宽,以千周为单位,在3分贝下测量。双调谐电路严格耦合。如果忽略调制频率的影响,由理论分析得出的方程在一定程度上得到了简化,并且可以表述由单调谐和双调谐电路引起的畸变。在大约每秒5000个周期的调制频率下,计算得到的失真与测量得到的失真非常接近。在这个频率下,观测值与计算值的偏离是相当明显的。推导了单调谐和双调谐电路的理论最大失真极限。对于单调谐电路,理论最大失真为Dnmax(单调谐电路)= 2λ/ΔW·100。对于双调谐电路,Dnmax(双调谐电路)= 4λ/ΔW·100。实验发现,为了确保无失真传输到每秒15,000个周期,与带宽和频率摆动相关的保守设计数字为ΔW/BW = 1/4。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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