1. the antenna will not emit electromagnetic radiation... the battery gives of direct voltage and cannot give suffiencient means to provide the antenna to make electromagnetic radiation. an antenna needs an alternating current for it to produce electromagnetic radiation.
2. light year equals 300,000 m/s: 300000 m/s * 3600s/1hr * 24hr/1day * 365day/year = 9.4608x10^12 m
3. 384,000 km ---> 3.84x10^8 m: so to and bck is 3.84x10^8 + 3.84x10^8 = 7.68x10^8... the speed of beam will be the speed of light which is 3x10^8 m/s.. so 7.68x10^8 m / 3x10^8 = 2.56 s