History
	n radio/wireless telegraphy – 1920: Marconi discovers shortwave (<100 m) radio n longwaves follow contour of land, require very high transmit power (200 kW+) n shortwaves reflect, refract, and absorb, like light (bounce of ionosphere, higher frequencies possible by vacuum tube (1906), cheaper, smaller, better quality transmitters) n other important dates – 1915: wireless voice transmission NY to SF – 1920: first commercial radio broadcast (Pittsburgh)