Historical clue formulations

• Method of communication needed to understand 17-, 25-, 36- and 49-Across — 2020-04-09
• Where S is ... — 2018-02-28
• Something you might tap in — 2012-05-13
• What a ham may use — 2011-07-23
• A ham might use it — 2009-01-23
• Communication means for emergencies — 1997-02-03