能請會通訊系統的大大幫個忙嗎??
這幾題都不知道怎麼解><
大大們謝謝了
1. Consider a square law detector, using a non-linear device shoes transfer function characteristics is defined by v2(t)=a1v1(t)+a2v12(t), where a1 and a2 are constants, v1(t) is the input, and v2(t) is the output. The input consists of the AM wave v1(t)=Ac[1+kam(t)]cos(2?趒ct). Please (a). Evalaute the output v2(t). (b). Find the conditions for which message signal m(t) may be recovered from v2(t).
2. Consider an AM receiver with envelope detection.
a. Write down a formula for e received AM signal including the narrowband Gaussian noise process. Explain each term in your formula..
b. Use both equation and phasor diagram to prove that when pre-detection SNR is large, envelope detection has the same post-detection SNR performance as coherent detection.
c. Use both equation and phasor diagram to prove that when pre-detection SNR is small, envelope detection has a threshold effect, i.e., the message signal is totally lost.
5. In general, the music program is transmitted by FM stations instead of AM stations, explain clearly what reasons it’s for?
7. The message signal m(t)=10sinc(400t) frequency modulates the carrier c(t)=100cos(2?趒ct). The modulation index is 6.
(a) Write an expression for the modulated signal s(t).
(b) What is the maximum frequency deviation of the modulated signal?
(c) What is the power content of the modulated signal?
(d) Find the bandwidth of the modulated signal using Carson’s law.
8. An angle modulated signal has the form s(t)=100cos[2?趒ct +4sin(2?趒mt)], where fc=10MHz and fm=1kHz.
(a) Assuming that this is an frequency modulated (FM) signal , determine the modulation index and the transmitted signal bandwidth.
(b) Assuming that this is an frequency modulated (PM) signal , determine the modulation index and the transmitted signal bandwidth.
[ 本帖最後由 max1130 於 2007-12-25 10:37 編輯 ] |
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