隧道與廣播

　　How come we can hear FM longer in a tunnel than AM?

　　為什么在隧道中調頻廣播比調幅廣播的信號要好一點?

　　It's because FM stations transmit at higher frequencies. They generally go from eighty-eight to one-hundred-and-eight megahertz. That's over a hundred million cycles per second.

　　這是因為調頻廣播臺的傳播頻率要頻繁些。通常在88到108兆赫。即每秒轉1億圈。

　　As a result, a single radio wave from an FM station is only a few meters long, about the size of a car. An AM station is putting out radio waves that are hundreds of times as long!

　　因此，調頻廣播電臺發出的一個電波的長度只有幾米，大概是一輛車的大小。而調幅廣播站發出的電波長達幾百米。

　　Long wavelengths tend to be absorbed or blocked as they try to enter the smaller tunnel. The higher-energy and shorter-wavelength waves from an FM station aren't absorbed or blocked as much. Instead, they tend to bounce around and get reflected off of surfaces, much like the inside of a tunnel.

　　在穿越隧道時，長的波長會被吞并阻礙。而來自調頻廣播高能量，波長又短的電波則不會被吞并或阻礙。相反的，它們會被隧道表面反射回來。

　　Of course, they only bounce so far. If the tunnel is long enough, even FM stations fade out until you come out the other end.

　　當然，它們只會在某個區域內反彈。如果隧道太長的話，即使是調頻廣播也會逐漸變弱直到駛出隧道。

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