Crystal RadioCrystal Radio

Presented by:Presented by:

ShrutiShruti NairNair(EEE-3(EEE-3rdrd yr.) yr.)

AkankshaAkanksha GargGarg(EEE-3(EEE-3rdrd yr.)yr.)

Structure of PresentationStructure of Presentation

IntroductionIntroductionMain parts of crystal radioMain parts of crystal radioWorking PrincipleWorking PrincipleSummarySummary

IntroductionIntroduction

. Crystal radios were the first widely used . Crystal radios were the first widely used type of radio receiver, and the main type type of radio receiver, and the main type used during the used during the wireless telegraphy era.

Crystal radios are the simplest type of Crystal radios are the simplest type of radio receiver, and can be handmade with radio receiver, and can be handmade with a few inexpensive parts, like an antenna a few inexpensive parts, like an antenna wire, tuning wire, tuning coil of copper wire, crystal detector and earphones .

They are passive receivers, while other They are passive receivers, while other radios use a separate source of radios use a separate source of electric power such as a battery or the mains power to amplify the weak radio signal

What is a crystal Radio?What is a crystal Radio?

A crystal radio receiver, also called a crystal set or cat's A crystal radio receiver, also called a crystal set or cat's whisker receiver, is a very simple radio receiver, whisker receiver, is a very simple radio receiver, popular in the early days of radio. It needs no battery popular in the early days of radio. It needs no battery or power source and runs on the power received from or power source and runs on the power received from radio waves by a long wire antenna. It gets its name radio waves by a long wire antenna. It gets its name from its most important component, known as a from its most important component, known as a crystal detector, originally made with a piece of crystal detector, originally made with a piece of crystalline mineral such as galena. This component is crystalline mineral such as galena. This component is now callednow called a diode. a diode.

[source: Wikipedia][source: Wikipedia]

The radio componentsThe radio components

Main Components::

AntennaAntenna Tuned circuitTuned circuit Crystal detectorCrystal detector EarphoneEarphone

AntennaAntenna

The antenna converts the energy in The antenna converts the energy in the electromagnetic the electromagnetic radio waves striking it to an alternating electric current in the antenna, which is connected to the tuning coil.

Since in a crystal radio all the power Since in a crystal radio all the power comes from the antenna, it is comes from the antenna, it is important that the antenna collect as important that the antenna collect as much power from the radio wave as much power from the radio wave as possible. possible.

Tuned circuitTuned circuit

The The tuned circuit, consisting of the coil and capacitor, acts as a resonator, analogous to a tuning fork for sound waves .

Electric charge flows rapidly back Electric charge flows rapidly back and forth between the plates of the and forth between the plates of the capacitor through the coil, oscillating capacitor through the coil, oscillating at the frequency of the radio signal .at the frequency of the radio signal .

Crystal DetectorCrystal Detector

A A semiconductor crystal  crystal detector which  which extracts the extracts the audio signal ( (modulation) from ) from the radio frequency the radio frequency carrier wave. It does . It does this by only allowing current to pass through this by only allowing current to pass through it in one direction, blocking half of the it in one direction, blocking half of the oscillations of the radio wave. oscillations of the radio wave.

ThisThisrectifies the  the alternating current radio  radio wave to a pulsing wave to a pulsing direct current, whose , whose strength varies with the audio signal. This strength varies with the audio signal. This current can be converted to sound by the current can be converted to sound by the earphone.earphone.

Cat’s Whisker DetectorCat’s Whisker Detector

Diode

Schematic Diagram of the Schematic Diagram of the RadioRadio

[ Source: Scott Lowe, http://www.angelfire.com/electronic2/index1/DmCrystalSet.html ]

Working Model of Crystal Working Model of Crystal radioradio

AM radio signal AM radio signal demodulationdemodulation

A. The Amplitude Modulated carrier is tuned in by the coil and variable capacitor.

B. The signal is rectified (detected) by the diode.

C. The carrier is filtered out and removed by the other capacitor leaving the audio signal.

UsesUses

These have become obsolete for These have become obsolete for commercial use. However they continue to commercial use. However they continue to be built by hobbyists, youth groups  as a be built by hobbyists, youth groups  as a way of learning about the technology of way of learning about the technology of radio. Today they are sold as educational radio. Today they are sold as educational devices .devices .

A crystal radio tuned to a strong local A crystal radio tuned to a strong local transmitter can be used just as a power transmitter can be used just as a power source for a second amplified receiver for source for a second amplified receiver for distant stations that cannot be heard with a distant stations that cannot be heard with a plain crystal radio.plain crystal radio.

Modern Crystal Radio with Modern Crystal Radio with piezoelectric earphonepiezoelectric earphone

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