你需要知道的調(diào)制器和解調(diào)器

　　你需要知道的調(diào)制器和解調(diào)器

　　調(diào)制，在RF應(yīng)用程序的上下文中，指兩個(gè)正弦信號(hào)的混合。射頻調(diào)制器是一種接收輸入信號(hào)并輸出調(diào)制信號(hào)的裝置。調(diào)制器基本上有兩個(gè)輸入和一個(gè)輸出。一個(gè)輸入通常稱為“信息”輸入。另一個(gè)輸入是rf載波輸入。

　　輸出信號(hào)是兩個(gè)輸入信號(hào)的復(fù)合。例如，在DVD播放器中，調(diào)制器將信號(hào)轉(zhuǎn)換為可用于電視接收機(jī)的格式。

　　解調(diào)器，另一方面，以調(diào)制信號(hào)和輸出的信息信號(hào)和載波信號(hào)。載波信號(hào)沒有得到進(jìn)一步的使用。在系統(tǒng)中，調(diào)制器放在發(fā)射機(jī)之前，解調(diào)器在接收機(jī)之后。

　　無論信號(hào)是話音還是數(shù)據(jù)，各種調(diào)制技術(shù)都可用，如模擬調(diào)制（調(diào)幅、調(diào)頻）和數(shù)字調(diào)制（頻移鍵控或FSK、幅移鍵控或詢問、移相鍵控或PSK）。

　　In amplitude modulation （AM or ASK）， the amplitude of the carrier varies in accordance to the information signal. In frequency modulation （FM or FSK）， the frequency of the carrier varies in accordance to the information signal. In phase modulation （PM）， the phase of the carrier varies in accordance to the information signal.

　　ASK can also be combined with PSK to create hybrid systems， such as quadrature amplitude modulation （QAM）， where both amplitude and phase are changed at the same time.

　　All have their pros and cons. ASK， for example， is simple to employ， but can be susceptible to noise. FSK is less susceptible to noise， but （in theory at least） requires a larger bandwidth/bitrate than ASK.

　　Similarly， PSK is less susceptible to noise and is bandwidth efficient， but requires synchronization in frequency and phase and therefore complicates receivers and transmitter design.