在野外这种干扰比较小，但是在城市就不见得了(城市往往是这种隧道的起点和终点)，众多的广播电台在诸多频段上不断地发出很大的噪声干扰，这种过滤手段就显得相当重要了。

In the wilderness such interference is rare, but in cities (where tunnels often start and finish) radio stations constantly blare out noise on many frequencies, making such filtering essential.

youdao