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簡簡單單 發問時間: 科學工程學 · 6 年前

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.

請各位前輩幫忙一下 用中文回答就可以了,完全不清楚題目要怎算...拜託了 感謝

已更新項目:

我看講義β是定義出來的,為什麼可以知道kf*Am/fm=β?

還有算式中為什麼要算最大頻率偏移?為什麼β<<1,BT=2fm

我知道窄頻是2fm,寬頻是2倍最大頻率偏移(書上寫的,可是我們這邊是怎麼推得的?)

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