A Simple Radio Receiver

The diagrams below detail the development of a simple modular radio receiver based entirely on circuits and devices studied during the Part IA course on Linear Circuits and Devices. This receiver may not take the market by storm! However, we hope it will help illustrate how the circuits and principles we are studying all c
A Simple Radio Receiver - schematic

ontribute to the art of electronic circuit design. A crystal set does not have a battery. It runs completely from the energy extracted from radio waves it picks up from the antenna. A resonant LC (or tuned) circuit coupled to a large aerial or antenna was used. Many amateur experimenters constructed crystal sets, often with the tuner inductor coil wound on a tubular box or a drinking glass. At this time the semiconductor diode had not been invented, so extracting the audible modulation signal from the transmission relied on the non-linear electrical properties of the `crystal`, typically a piece of coke or galena. In early sets a "cat`s whiskers" - a fine piece of wire - was adjusted by trial and error to make a suitable contact with the crystal. There were many limitations to the crystal set: it needed a big aerial (antenna), an earth connection, the clumsy cat`s whisker, and the weak signal could only be listened to by one person at a time with headphones. Very quickly the crystal set began to be replaced by valve radios with loudspeakers, powered by batteries. In World War II, crystal sets were used by prisoners of war in prison camps to listen to news from home. Much ingenuity went into improvising the necessary components. The design shown here is a little more complex than strictly necessary, but some of the adaptations incorporated make it easier to develop the design, adding amplifiers and other stages as we meet...

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