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A transmitter and a receiver

  1. Dec 25, 2003 #1

    I am going to have a science exhibition in the first week of February and our professor has asked us to make a project (that works!!). He wants it by mid-January though. Anyway I decided to make a transmitter and a receiver (like a transmitter and a radio). I saw the popular Rough Science show that comes on T.V. and got a few ideas. I also visited their informative site, but it was not informative enough. I checked out their chalenge and did not quite understand it. Anyway the link to the site is :

    http://www.pbs.org/weta/roughscience/challenges/transmitter/ [Broken]

    I would really appreciate it if someone reads the concept above and explains in detail how the transmitter and the radio worked. (note: it has to be homemade so I would like to be just like the one made by the Rough Scientists).

    Thank you

    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Dec 25, 2003 #2
    A normal radio has to be tuned to the station you want to recieve. For instance, if you tune your reciever to 104.0 MHz, then only the one station will be recieved that transmits at 104.0 MHz (if there is one).
    The idea of a spark transmitter is, that it transmits at *all* frequencies (That's why it's illegal). In a spark, the electric field suddenly breaks down, i.e. changes from maximum to zero in a very short time interval. Any reciever will respond to this, no matter how it's tuned.
    (BTW, a spark transmitter was what Heinrich Hertz used when he discovered radio waves.)
    Basically, you get a spark every time you open or close an electric contact. In order to transmit information, one spark will of course not be enough. You got to use a device that produces many sparks per second, so you can send 'long' and 'short' signals, as used in the Morse code.
    Such a device is called a 'buzzer'.
    There are a lots of devices that do this. Electric motors, for instance. Or old-fashioned electric doorbells which go 'rrrrrrrrrrring'. The website that you mention gives a sketch of such a doorbell.
    However, these devices only produce small electric fields (low voltage). That means the transmission range will be small. You got to transform to high voltage. Your website says you need a transformer. However, it's not exactly exlicit on how to build one. Maybe a websearch on 'transformer' will help. Or even 'tesla transformer' .
    Concerning the reciever, I think it's OK if you use any old radio. Building a homemade reciever is a lot of trouble, so why bother? Anyways, you got only 2 weeks left...
  4. Dec 26, 2003 #3

    Actually I would appreciate it if you could please explain the circuit to me. I have all the items needed, only thing is I dont know where each item is to be placed in the circuit. Also the thing is acording to my knowledge, a spark was formed (in the show) between two metals. I mean that we could see the spak being formed. As far as I have understood, in the circuit shown on the website, there is no 'place' for the spark to be shown. I would like the circuit of the transmitter to be explained in detail.

    Thanks once again,

  5. Dec 29, 2003 #4

    I understood how to make a radio and also have understood the whole
    concept properly. The only thing I am not sure of are the parts:
    antennae and ground. I am supposed to attach these two also. I would
    like to know what makes up the antennae and the ground? Is just a
    normat copper wire (long one though) be used as an antennae? Also what is the 'ground' made of and where to be place it (not in the circuit of the radio)? Do we just bury it in the ground?

    Thank you for the trouble,
  6. Dec 31, 2003 #5
    The antenna is the aerial. If a fluctuating radio wave passes a long wire, orientated in the same plane as the 'E' field of the signal, then the electons in the wire will oscillate at the same frequency as the signal. This is how you pick up your signal.
    My home made set has a wire about 5 metres long, although almost any orientation of it works sufficiently with a strong radio station.

    The 'ground' does not need to be buried no. It refers to the side of the circuit at zero potential.

    Try this site for help and useful links: http://www.midnightscience.com/project.html [Broken]
    Last edited by a moderator: May 1, 2017
  7. Feb 18, 2010 #6


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    hi there
    I am a Software Engineer. I need to make an RF transmitter/receiver for my cell phone. The area in which I live has a signal problem. If I go to my 3rd floor I receive signals on my cell phone other than that my cell phone shows no signals. Kindly help me how to make it.
  8. Feb 18, 2010 #7
    This seems way off the original school science project, which in any case is past its due date.

    Also, I think you are in for trouble if you start retransmitting cellphone frequencies. Remember that the network is at least UHF, and it is bi-directional. You are likely to cause interference to other users and get into legal problems if you try this.
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