Previously, their presence was revealed only in the radio spectrum.

在此之前，只能在无线电频谱中发现它们的存在。

But there is only a limited amount of radio spectrum available.

但可用于通信的无线电频段是有限的。

Unfortunately, some parts of the radio spectrum are full of signals created by Earthlings, rather than aliens.

不幸的是，来自地球居民而不是外星人的信号挤满了射频频谱的一部分。

On the plus side, the visible light spectrum can handle way more traffic than wi-fi's already crowded radio spectrum.

另外, 相比wi-fi拥挤的无线电频谱，可见光谱可以应对更多的传输方式。

With growing demand for wireless devices, passive radar would allow the radio spectrum currently used by conventional radar to be freed up and auctioned off to mobile operators.

随着无线设备的需求不断增加，被动雷达能够将目前用于传统雷达的无线电频谱解放出来，然后再拍卖给移动运营商。

In the U.K. for example, 3G and 4G networks were relatively cheap to set up because they were able to roll out on existing frequencies, on the country’s radio spectrum.

例如，在英国，3G 和 4G 网络的建立成本相对较低，因为它们能够在该国无线电频谱的现有频率上推出。

This leads consumers to pay for more bandwidth, pushing service providers to take over more of the radio spectrum and eventually send more satellites into the sky, creating a vicious cycle that could eventually blot out the stars.

这导致消费者支付更多的带宽，迫使服务提供商接管更多的无线电频谱，最终向天空发射更多的卫星，形成一个恶性循环，最终可能会掩盖住星星。