In the beginning of broadcasting "detectors" (crystal sets) were used to receive broadcast stations. Broadcasting started in Germany in the year 1923 (USA 1919- 1920, Australia 1921?, France 1921, England 1922, New Zealand 1923, Switzerland 1923, Austria 1924).
The detector usually made headphone reception possible. The detector obtains the complete energy from the transmitter signal. An additional voltage supply wasn't required. Exception: detectors with rectifier material, that required an additional bias voltage .
The detector receiver (crystal receiver) has the following components: Coil and variable capacitor (resonance circuit), rectifier, headphone, aerial (antenna), earth (ground).
Inventor of crystal receiver: Karl Ferdinand Braun, crystal rectifier1874, point contact for crystal rectifier1898, crystal receiver1906.
The selected radio frequeny (r.f.) signal was converted to audio frequency (af) and supplied the headphone with a.f. via the rectifier. Early rectifiers were difficult to handle. A small wire tip had to be pointed exactly at the semiconductor material. Later, available Germanium semiconductors (e.g. 1N34) were used. Good crystal receivers could very well separate several transmitters from each other and even offered long-distance reception. Special attraction of the crystal receiver is 'free-power' reception.
The crystal sets were replaced soon by tube receivers . These receivers were more potent and more selective. In addition, these radios offered loudspeaker reception. Even today you can order construction kits and components for building crystal sets.
In Germany the good times of b.c.-band (MW) broadcast is over. Many transmitters use only transmit powers of under 5 KW. Today most transmitters are already tested in digital modulation, this means the end of crystal receivers because of their non-ability to decode such moldulation. We still enjoy the last couple of years. My home brew crystal set receives up to 55 radio stations of 22 European countries at night.
More information about early crystal rectifiers and germanium diodes you will find at my "Wumpusīs Old Radio World" pages.
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