No time to erect an antenna? Maybe you just need a long wire and a tree. From the annals of MAKE:blog comes information on pneumatic antenna launchers. These are a variation of the potato cannon and may be the first serious use of these cool contraptions. Well, I guess T-shirt cannons and tornado-simulating 2x4 cannons rate also. The site is packed with info on this application and has lots of related links. The site owner sells kits but these links seem to be non-functional at the moment.
This, along with a HAM radio, should be penciled into everyone's copy of A Steampunk Guide to the Apocalypse.