热度 7
2015-4-7 00:00
4726 次阅读|
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主要是为了测试下变频对信号信噪比的影响。 下变频主要包括:频率搬移+低通滤波+抽取信号来实现 代码如下: close all;clc;clear all; fs = 150e6; %原始数据采样率 fc = 46.519e6;%信号中频 fdown = 30e6;%下变频率 n = fs*0.001; bit_width = 8 ts = 1/fs; nn = ; fid = fopen('D:\work\常用重要\test_xiabianpin20150324\RxRec20150323_181158.dat','r'); data = fread(fid, ,'bit8'); figure pwelch(data) %下变频 data_i = data .* lianghua_bit(cos(2*pi*fdown*ts*nn),bit_width)/2^bit_width; data_q = data .* lianghua_bit(sin(2*pi*fdown*ts*nn),bit_width)/2^bit_width; figure pwelch(data_i) % figure % pwelch(data_q) %低通滤波 fir_conficient = fir1(20,0.2); figure freqz(fir_conficient,1,512); data_out_i = filter (fir_conficient,1,data_i); data_out_q = filter (fir_conficient,1,data_q); figure pwelch(data_out_i) % figure % pwelch(data_out_q) %抽取 for i = 1:floor(length(data_out_i))/3 x_i(i) = sum(data_out_i((i-1)*3+1:(i-1)*3+3))/3; end for i = 1:floor(length(data_out_i))/3 x_q(i) = sum(data_out_q((i-1)*3+1:(i-1)*3+3))/3; end %然后把数据考到另一组程序中对信号采集信号信噪比进行检测 运行结果如下: 原始信号频谱: 把频谱搬移后的图把频谱搬移后的图: 低通滤波器的幅频特**: 滤波之后的频谱图: matlab中下变频基本这个过程了。