Broadcast radio receiver
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The most familiar form of radio receiver is a broadcast radio receiver, often just called a broadcast receiver or simply a radio, as used for radio broadcasting. It receives audio programs intended fo
A portable battery-powered AM/FM broadcast receiver, used to listen to audio broadcast by local radio stations.
A bedside clock radio that combines a radio receiver with an alarm clock
Amplitude modulation
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Amplitude modulation is a signal modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the instantaneous amplitude
One of the crude pre-vacuum tube AM transmitters, a Telefunken arc transmitter from 1906. The carrier wave is generated by 6 electric arcs in the vertical tubes, connected to a tuned circuit. Modulation is done by the large carbon microphone (cone shape) in the antenna lead.
One of the first vacuum tube AM radio transmitters, built by Meissner in 1913 with an early triode tube by Robert von Lieben. He used it in a historic 36 km (22 mi) voice transmission from Berlin to Nauen, Germany. Compare its small size with the arc transmitter above.
Figure 3: The spectrogram of an AM voice broadcast shows the two sidebands (green) on either side of the carrier (red) with time proceeding in the vertical direction.