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TFM(平滑调频)具有优良的频谱特性,是适合数字移动通信的一种调制方式。本文首先简要介绍 TFM 的原理,然后详细阐述采用正交调制方案产生 TFM 的方法。对于由低通和延时衰减的组合网络构成的予调制滤波器进行传输特性计算,并检验和修正其冲激响应使之符合奈氏定则,从而说明确定 TFM 相位特性的方法。研制中,以截距为5T、取样速率为8f_b 计算 TFM 相位特性取样点上的相应数值、并用两个只读存储器分别实现具有1024个数据的正弦表和余弦表。列出了产生 TFM 的实际电路,获得的试验结果表明这种数字化设计的电路简单,工作稳定。可应用于数字式移动电台设计。
TFM (Smoothing Frequency Modulation) has excellent spectral characteristics, is a modulation method suitable for digital mobile communications. This paper first briefly introduces the principle of TFM, and then elaborates on the method of generating TFM using orthogonal modulation scheme. The method of determining the phase characteristics of the TFM is described for the transmission characteristics of a pre-modulated filter consisting of a combined network of low-pass and delay-attenuated filters, whose transmission response is verified and modified to meet Ney’s rules. During the development, the corresponding values of the sampling points of the TFM phase characteristics are calculated with an intercept of 5T and a sampling rate of 8f_b, and sine and cosine meters with 1024 data are realized respectively by using two read-only memories. The actual circuit that produces TFM is listed, the test result that obtains obtained shows this digital design circuit is simple, the job is steady. Can be applied to digital mobile station design.