May 7 – Radio Day

Radio Day is marked on May 7. This is a holiday for all communication workers. However, is it observed only in former Soviet Republics and in Bulgaria. According to the official Soviet version, a Russian physicist Alexander Popov constructed the first radio receiver and held a communication session in 1895.

To tell you the truth, critics note that the first communication session was held by the discoverer of radio waves Heinrich Hertz and that Popov’s radio receiver was an improved modification of Oliver Lodge's coherer. 

“Wikipedia” informs that the date was celebrated in the USSR in 1925 for the first time and has been annually marked since 1945.