Notices
Results 1 to 3 of 3

Thread: Crystal Radio

  1. #1 Crystal Radio 
    Junior Member
    Join Date
    Aug 2014
    Posts
    2
    Can someone please tell me the basics to how a cystal radio works? And also what are all the components that makes up a crystal radio? Thank you!!
    Reply With Quote  
     

  2. #2  
    Senior Member
    Join Date
    Jan 2013
    Posts
    427
    Quote Originally Posted by dan1007 View Post
    Can someone please tell me the basics to how a cystal radio works? And also what are all the components that makes up a crystal radio? Thank you!!
    There are many, many websites devoted to crystal radios. The wikipedia entry is probably a good place to start.

    I built many of these as a child and remember them with fondness. I don't know how much background you have in electronics, so I'll give you a simple explanation. If it is too elementary, just post back with more information about what you do know already.

    An AM radio signal is called AM because it carries your voice, music, etc., in the form of amplitude modulation. That's a fancy term for "variation in amplitude" or "variation in signal strength." A 1MHz radio wave carries on it your audio signal encoded as those variations.

    The AM radio signal received by your antenna has zero average value -- it spends equal amounts of time going positive and negative. Your ear cannot follow 1MHz signals, so you will hear only the average, which is zero.

    The "crystal" is a diode. A diode, for the purposes of our simplified discussion, is a one-way valve for current. So a crystal will "chop off" either the positive- or negative-going parts of the received signal. Now we get something that has a nonzero average value. Hook that signal to some sensitive headphones, and you have a simple radio. No batteries required, since you are using only the energy of the incoming radio signal.

    The foregoing actually works as a radio, but lacks selectivity. All radio signals in your area will be heard simultaneously unless you add some sort of tuning element. The simplest tuning is achieved with an inductor (coil) and a capacitor. The inductor stores energy in a magnetic field, and a capacitor stores it in an electric field. Energy can slosh back and forth between these two fields, just as energy flows between kinetic and potential energy in a spring-mass system. Incoming signals at or near the natural resonant frequency of this energy exchange will pass through to the diode, while others will be weakened.

    That's the short version.

    Build one and enjoy! [The tuning element should use an inductor of about 250 microhenries and a variable capacitance of a maximum value of about 350 picofarads, to tune the AM broadcast band.]
    Reply With Quote  
     

  3. #3  
    Junior Member
    Join Date
    Aug 2014
    Posts
    2
    hey Thank you so muuuch for this infomation! I am writing an assignment on this right now and is due in 3 weeks~ The assignment is to write about the crystal radio and what all the components do. This is what I have written so far...

    The crystal radio
    Most radios which we buy and use nowadays contain a complex electronic system which makes a strong copy of sound. A crystal radio is the simplest kind of radio that simply picks up the wave and converts it into sound. A crystal radio does not require separate power or batteries to make the sound stronger; instead, it gets all its power solely from the radio wave. The radio is named as a crystal radio kit because of the crystal diode which is one of the most crucial parts that makes the radio work. The diode has a high resistance to current in one direction and a low resistance in the other direction thus, the diode allows the electrons to flow in one direction only. This therefore will convert the alternating current (AC) to direct current (DC) which is what the majority of electrical devices work in. The amplitude modulation (AM) is a modulation technique used in electronic communication which is mostly used for communicating information via radio carrier wave. AM has the ability to vary the amplitude of the carrier in proportion to the waveform being sent, hence alternating current. This allows the radio to work without a power supply.
    A radio station sends us its speech and music using radio waves which come in a form of electromagnetic waves that travel between the stationís transmitter and the crystal radioís antenna. This wave makes the electrons in the antenna move back and forth (alternating current).
    Reply With Quote  
     

Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •