Crystal Radio
A crystal radio uses no active parts: it is powered only by the radio signal itself, whose detected power feeds headphones in order to be audible at all. In order to achieve even a minimal sensitivity, a crystal radio is limited to low frequencies using a large antenna (usually a long wire). It relies on detection using some sort of semiconductor diode such as the original cat's-whisker diode discovered long before the development of modern semiconductors.
- Advantages
- Simple, easy-to-make. Here we see a classic design for a clandestine receiver in a POW camp.
- Disadvantages
- Insensitive, it needs a strong RF signal and/or a long-wire antenna to operate.
- Poor selectivity since it only has one tuned circuit.
Read more about this topic: Radio Receiver Design
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