POSSIBLE REFERENCE TO MORE THAN ONE WORD

Does they refer to the signals or the airwaves? The editing clarifies what is being limited.

REFERENCE IMPLIED BUT NOT STATED

What does which refer to? The editing clarifies what employees resented.

A pronoun — a word such as she, yourself, her, it, this, who, or which— should refer clearly to the word or words it replaces (called the antecedent) elsewhere in the sentence or in a previous sentence. If more than one word could be the antecedent, or if no specific antecedent is present in the sentence, edit to make the meaning clear. (See 34f.)