sentence: Earth's ionosphere, they are ideal for some of the worse-case emergency scenarios.
sentences_before: Because of the nature of radio wave propagation, communications made via short-wave radio can be intercepted and heard by anyone with the proper equipment and knowledge.
sentences_after: One disadvantage may be that one requires training and licensing to operate a short-wave radio, in many countries.
concept_name: earth
headings: Emergency communication system Broadcast Technologies Infrastructure-Independent
categories: Emergency services Communication