# 寫通訊題目遇到的難題

ps:Ac,Θi(t),fi(t),fc,kf後面的小寫英文都是在下標

1. Let us consider an angle-modulated wave which is given by s(t)=Ac*COS[Θi(t)]

where Ac is carrier amplitude and Θi(t) denotes the angle of a modulated

sinusoidal carrier at time t.

The instantaneous frequency fi(t) of the angle-modulated signal s(t) is defined

as:fi(t)=[1/(2pi)]*[dΘi(t)/dt]

For frequency modulation(FM) fi(t) is varied linearly with the message signal m(t),

or fi(t)=fc+kfm(t).

(a)

Please find the frequency modulation index β of sinusoidal message signal

m(t)=Am*COS[2pi(fm)t], if β is small compared to one radian find the

transmission bandwidth of s(t).

(b)

Repeat part(a) if message signal m(t) is non-sinusoidal message with baseband

bandwidth W.

(c)

Please explain in detail the indirect method for generating a wide-band FM wave.

### 2 個解答

• 小黑
Lv 6
6 年前
最佳解答

參考看看，不確定正確。

2014-01-12 16:21:16 補充：

β定義就是 最大頻率偏移/訊息頻寬

你看(c)小題sNBFM(t)的信號樣子，去分析他的頻寬就會是2倍訊息頻寬。

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• 6 年前

參考下面的網址看看

http://phi008780520.pixnet.net/blog

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