問題描述：

MATLAB關于產生線性調頻信號的問題

t=10e-6; %線性調頻信號時間長度

fs=40e6; %采樣頻率

ts=1/fs;

fc=9e6; %線性調頻的起始頻率

f0=10e6; %本振信號的中心頻率

B=2e6; %線性調頻信號調頻帶寬

ft=0:1/fs:t-1/fs; %調制信號,對于線性調頻來說,調制信號就是時間序列

N=length(ft);

k=B/fs*2*pi/max(ft); %計算調制靈敏度

x1=modulate(ft,fc,fs,'fm',k);

最后的那句是什么意思,modulate函數的用法及個參數意思~

1個回答

分類：

英語

2014-12-07

問題解答：

我來補答

樓主要學會用MATLAB的help命令啊：

help modulate

MODULATE Signal modulation for communications simulations.

Y = MODULATE(X,Fc,Fs,METHOD,OPT) modulates the message signal X with a

carrier frequency Fc and sampling frequency Fs,using the modulation

scheme in METHOD.OPT is an extra sometimes optional parameter whose

purpose depends on the modulation scheme you choose.

Fs must satisfy Fs > 2*Fc + BW,where BW is the bandwidth of the

modulated signal.

METHOD MODULATION SCHEME

'am',Amplitude modulation,double side-band,suppressed carrier

'amdsb-sc' OPT not used.

'amdsb-tc' Amplitude modulation,double side-band,transmitted carrier

OPT is a scalar which is subtracted from X prior to

multiplication by the carrier cosine.It defaults to

min(min(X)) so the offset message signal is positive and

has a minimum value of zero.

'amssb' Amplitude modulation,single side-band

OPT not used.

'fm' Frequency modulation

OPT is a scalar which specifies the constant of frequency

modulation kf.kf = (Fc/Fs)*2*pi/max(max(abs(X))) by

default for a maximum frequency excursion of Fc Hertz.

'pm' Phase modulation

OPT is a scalar which specifies the constant of phase

modulation kp.kp = pi/max(max(abs(x))) by default for a

maximum phase excursion of +/-pi radians.

'pwm' Pulse width modulation

If you let OPT = 'centered',the pulses are centered on the

carrier period rather than being "left justified".

'ppm' Pulse position modulation

OPT is a scalar between 0 and 1 which specifies the pulse

width in fractions of the carrier period.It defaults to .1.

'qam' Quadrature amplitude modulation

OPT is a matrix the same size as X which is modulated in

quadrature with X.

If X is a matrix,its columns are modulated.

[Y,T] = MODULATE(...) returns a time vector the same length as Y.

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