Simple Radio Transmitter ?

Discussion in 'Wireless & RF Design' started by Mazaag, Dec 21, 2007.

  1. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
    255
    0
    Hey guys,

    I came across this the other day...

    http://electronics.howstuffworks.com/radio1.htm

    Could someone please explain how radio waves are produced when you short the leads of the battery with a coin ?

    And is the radio wave produced of a certain frequency ( I would imagine that it wouldn't be, because you you would then have to tune to that frequency to hear the crackle)?

    and what about the carrier wave and so forth, where does all that come into play by shorting the leads? I understand that an AM signal requires a carrier wave in which the message signal (crackle in this case) is superimposed onto...how does that happen here ?

    Thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Those are sparks that produce the RF. And, no, there is no certain frequency produced. The RF energy is spread out all over the radio spectrum. There is no modulation placed on the RF, so the concept of a carrier wave does not fit the phenomena here.

    This is more like radio back before De Forest and the vacuum tube. Radio was Morse code by sparks, and whatever tuning was done was by passive LC filters. The received RF was developed across a spark gap, and at first had to be observed with a microscope. Google things like "rotary spark gap" and "variometer" for more. A copy of "Elements of Radio" by Lt.Cdr Ellery W. Stone, copyright 1919, will teach you all about spark gap radio techniques.
     
  3. narced

    New Member

    Dec 22, 2007
    3
    0
    Think about switch bounce. Lets say you make 10 connections to the battery in 1 second. Then your carrier frequency is 10hz. Your amplitude is the measure of the burst of energy emitted.
     
  4. Winston

    Member

    Dec 25, 2007
    22
    0
    First, I think a beginner explains things best to another beginner. Secondly, I humbly request correction/clarification on what I know are mistakes in the following. Many thanks.

    When an electron(s) is made to move - that is, accelerate, a magnetic field expands out from it (why? who knows, that's just the way things are). This moving/accelerating m field creates an electric field (that field that exists between your finger and a door knob when there's an excess of electrons on your body causing a zap). This e field makes another m field, which makes another e field, and so on forever out into space at the speed of light. It's one burst, so I don't know how to say what the frequency would be. I guess if it's a flat wave, it's a burst that lasts a whole second, or half a second, or a quicker burst would be a smaller fraction of a second, it all depends on how quick that one burst is, I guess...

    Now, because it's a dc current, the e's in the coin are in a constant uniform movement, just scooting along, which is not "acceleration", a change in the *rate* of movement - getting faster and faster, then slower and slower, forming a wave when it's graphed on an oscilloscope. So, I imagine that it is the spark itself when the coin is touched to that terminal which causes the radio burst, because the electrons in the ionized air, the spark, accelerate and then slow down during the time of that zap. Lightening makes the tv and radio go, "tzt" for the same reason. One quick (I've heard it's a very high frequency) jerk of electrons along a jagged channel of ionized air.

    Hope that makes sense.
     
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