What is the topic of the passage? [br] [originaltext] Some people say radio

Some people say radio was invented by Guglielmo Marconi of Italy. Marconi sent the first radio communication signals through the air in eighteen ninety-five. In fact, no one person can be called the inventor of radio. Many people, including several Americans, helped to develop radio.
    De Forest developed some of the technology used in early radio. During his lifetime, he invented hundreds of devices that were used in telephones, shortwave radio broadcasts, and similar technology. His most famous invention was the vacuum tube, or electron tube. In nineteen-O-six, the electron tube was considered the single most important development in electronics. The device made it possible to strengthen radio signals and to send them over long distances. It was a major reason for the fast growth of the electronics and communications industries in the early part of the twentieth century.
    Edwin Armstrong was another American inventor who was important in the development of electronics and radio communication. Armstrong developed technology that helped to improve radio reception. He discovered ways to limit unwanted radio signals. Edwin Armstrong also was a leader in using radio to reproduce sounds clearly. This process became known as frequency modulation, or FM radio. FM radio provided better sound reproduction and less noise or interference than traditional AM radio. Armstrong also developed radio receivers that became widely used.