crystal receiver การใช้

In the 1920s the crystal receiver was superseded by vacuum tube receivers and became obsolete.
The inaugural radio broadcast was in 1920 over Pittsburgh station KDKA . A year later Westinghouse produced a crystal receiver that required no headphones.
The earliest crystal receivers did not have a tuned circuit at all, and just consisted of a crystal detector connected between the antenna and ground, with an earphone across it.
All semiconductor detectors function rather inefficiently in crystal receivers, because the low voltage input to the detector is too low to result in much difference between forward better conduction direction, and the reverse weaker conduction.