A radio signal was sent to the spacecraft.

向宇宙飞船发出了无线电信号。

《牛津词典》

The simple detection of a radio signal will be sufficient to answer this most basic of all questions.

对无线电信号的简单探测就足以回答这个最基本的问题。

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A radio signal has both electrical and magnetic properties.

无线电信号既具有电的特性也具有磁的特性。

《柯林斯英汉双解大词典》

Or maybe,instead of a radio signal, an alien civilization sent us something physical.

VOA: standard.2010.04.16

AM radio can be sent over larger distances, but the quality of the sound is not as good as a later kind of radio signal processing, called frequency modulation.

VOA: special.2010.12.08

Would the sending of a radio signal to activate this system constitute a trespass to chattels?

FORBES: Scalia Finds 18th-Century Precedent For GPS Search

The fences work by burying a boundary wire which transmits a radio signal to a collar.

BBC: Monima O'Connor, Russell George and William Powell

This new wireless remote system operates from a radio signal rather than infrared light, dramatically increasing functionality and range.

ENGADGET: Nikon D5200 to reach US photographers in late January for $900