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How to send and receive radio waves?

  1. Aug 13, 2010 #1
    Hey guys, been trying to Google tons of things but am striking out.

    I'm curious how the process of sending and receiving radio waves works. What I'm looking for, more specifically, is how do you send specific wavelengths and amplitudes and then once those waves are airborne, how do you create something to receive them?

    Everything I was finding on Google was just telling me to buy X piece of equipment to send and buy X piece of equipment to receive, but nothing really told or showed me HOW the process actually works.

    If anyone knows of a guide, tutorial, or maybe even the correct keywords to search for, I'd appreciate it. Thanks.
     
  2. jcsd
  3. Aug 13, 2010 #2
    You could emit radio-waves by accelerating electrons through a voltage . Like in an electron gun or crookes tube . And you could vary the voltage . This is how your microwave emits photons . I don't know if this is how the radio stations do it .
     
  4. Aug 13, 2010 #3
    Well basically I have some hypothesis about things that you might be able to do with radio waves (more thinking outside the box stuff). In order to test this, I'd have to be able to send a wide spectrum of radio waves and also be able to receive them. Obviously I could just purchase equipment to do this for me, but I'm a "know-how" type of guy and I'd like to know how.
     
  5. Aug 13, 2010 #4
    what are you trying to do with the radio waves what are you testing ?
    You could try building an electron gun by using a heated cathode like maybe an electric oven element and heat this with current . then put this in a pvc tube , and then attract the electrons over a voltage and when the electrons travel from the cathode to the anode they will emit light , and you can vary the voltage . and then you could receive them with a household radio , or maybe try building a photomultiplier ,
    And you would haft to evacuate the air out of the tube for best results .
    You want the cathode heated so it will emit electrons easier and this is called thermionic emission . .
    Or maybe you could shoot the radio waves at a fluorescent tube and it might cause enough current to flow to get a reading in amperes on your meter . similar to how a Geiger counter works .
     
    Last edited: Aug 13, 2010
  6. Aug 13, 2010 #5
    My idea is that taking how visible light refracts and reflects into our eyes to create a visible image of our surroundings, I can do the same with radio waves. If I were to fire a spectrum of radio waves at various elements and measure its reflections, I could then fire a spectrum at a larger area and re-create the scene at an atomic level. At first it would start with little precision, showing us something similar to Atari or Nintendo graphics, but with the advances of the technology could potentially produce fully 3-dimensional representations of rooms.

    The idea is better than visible light because radio waves pierce through tons of solid objects. This type of device could potentially be like a giant x-ray gun.

    Unfortunately I'm just an amateur hobbyist, with no real physics background, so it's probably impossible, but I thought I'd experiment with radio waves anyways and try to learn more about how they work.
     
  7. Aug 13, 2010 #6
    it sounds similar to how a scanning electron microscope works , only using radio waves .
     
  8. Aug 13, 2010 #7
    I have no idea what you mean by 'recreating the scene at an atomic level', but you
    sound like you're not aware of the restrictions on resolution imposed by diffraction.

    Before going on, you should first consider what the wavelength range for radio waves
    is versus the typical spatial dimensions of the objects you intend to image.
     
  9. Aug 13, 2010 #8
    This is an insanely complex, difficult, inefficient, and generally wrongheaded and dangerous way of approaching the problem of "producing radio waves". Some specific high-frequency, high-power, narrow-band applications use specialized vacuum tubes such as magnetrons and klystrons. The details of their operation are far more complex than you describe, and their design and construction is very non-trivial. And from the information given, unnecessary...free electrons are not required for the production of radio waves, the vast majority of radio transmitters simply use an alternating current coupled into an antenna of the appropriate length to efficiently radiate at the chosen frequency. Your suggested electric oven element in a PVC tube is only an electrical and fire hazard, you're almost certain not to observe any thermionic emission, let alone get useful radio wave emission. And a photomultiplier tube, aside from also being extremely difficult to design and construct, will require operating voltages of thousands of volts and would only receive radio waves as incidental interference.


    You are essentially talking about an imaging radar system...an extremely complex and difficult project, unfortunately. It's not just a matter of producing radio waves, you have to emit them in highly directional beams, detect and measure the strength of the weak reflections, time the echoes of something that moves at one foot per nanosecond (you need timing for ranging, intensity measurement alone won't do)...even a simple radar ranging system takes a lot of difficult engineering. Also, radio waves are far lower frequency than visible light, meaning larger wavelengths...tens of cm for the high frequency microwaves used by WiFi and microwave ovens, tens of meters to kilometers for AM/FM radio frequencies. This is a fundamental limiting factor in how sharply you can focus a beam with an antenna array of a given size, and in the sort of detail you can image with radar at that frequency. Imaging radar systems exist (http://www.planetary.org/explore/topics/saturn/titan_radar.html [Broken]), but you'd have a hard time finding one that could produce a recognizable image of a room.

    Sonar is much more achievable. There are simple sonar ranging devices available as ready-made modules (http://www.radioshack.com/product/index.jsp?productId=2909789), and it's far more reasonable to expect to home-build a complete sonar system (still a major project, and it sounds like you've got a lot to learn before you could make real progress on it, but achievable with hobbyist equipment and budget). Light travels about 30 cm per nanosecond, 300 km per millisecond. Sound travels about 34 cm per millisecond, and cheap microcontrollers can easily measure events with sub-millisecond resolution. Sound is also much easier to emit and detect.
     
    Last edited by a moderator: May 4, 2017
  10. Aug 13, 2010 #9
    Wouldn't a basic answer to the question be something like:
    Build an LC oscillator circuit with the correct capacitors and inductors, hook it to a dipole antenna of the right length, then drive/watch the voltage to send/receive radio waves.
    Calculations for the antenna, L and C are left as exercises for the reader.
     
  11. Aug 13, 2010 #10

    jtbell

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    Staff: Mentor

    Or if you have cable TV, connect the incoming feed to a TV antenna, which will turn it into a small broadcasting station. Then wait for the Federal Communications Commission (or the equivalent agency if you're outside the USA) to come after you for interfering with your neighbors' TV reception. If you have any neighbors who still use broadcast TV, that is. :uhh:
     
  12. Aug 13, 2010 #11
    True; I think your answer is appropriate, AC Power; building a simple radio transmitter and receiver was standard electronic "build it yourself kit" stuff when I was a kid; 'tis a shame you don't see much of that stuff on the market anymore....
    So in lieu of that...the answer to the question.....

    is...
    ...simply press "30" on your microwave even; then hit "start" and you will be producing 2.45 GHz EM waves,,,,(about 12 cm wavelength).

    A potato will suffice.

    PS. the temperature of the potato will increase as the EM waves are "received". ;))

    :))
     
    Last edited: Aug 13, 2010
  13. Aug 13, 2010 #12
    You could rub a balloon on your hair, this would give it a charge.

    Then you can then emit various frequencies by shaking your hand at varying speeds.

    The most elementary radio emitter I can think of.
     
  14. Aug 13, 2010 #13

    jambaugh

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    Science Advisor
    Gold Member

    I typed up a quick Blog entry:
    https://www.physicsforums.com/blog.php?b=2198" [Broken]
     
    Last edited by a moderator: May 4, 2017
  15. Aug 13, 2010 #14
    Here in thumbnail is a block diagram of an AM radio transmitter I built and used to broadcast on the AM radio band about 1958. It had a range of about 10 miles. V1 was an old WW II military surplus transmitter tube (about 8 cm diameter). The antenna was a horizontal wire in the attic, about 15 meters long. Standing waves in the antenna could be detected using a fluorescent lamp tube. For obvious reasons, I never turned it on for more than about 15 minutes at a time.

    Bob S
     

    Attached Files:

  16. Aug 13, 2010 #15
    A little overly specific...any oscillator will do. The LC tank circuit will be useful for both transmission and reception, though. There's also self-contained crystal oscillators that can easily be used to generate a given frequency with high precision...just apply power. Do check out local regulations about unlicensed radio.

    Back to the original question...search for AM radio circuits (much simpler to understand than FM), look for websites by HAM radio enthusiasts. Look up crystal radios...you'll find information on how antennas pick up signals and how the tuned tank circuits select a given frequency, without a bunch of amplifiers in the way. If you're in an area that has them, check out the electronics lab kits from Radio Shack. Find someone who knows some electronics and bug them when you have questions. Find an ARRL Handbook...library might have it.
     
  17. Aug 13, 2010 #16

    Born2bwire

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    I just use a bank of randomly tuned spark gap generators.
     
  18. Aug 13, 2010 #17
    I learned quite by accident you can easily interrupt just about any broadcast TV in the house (the old VHF broadcast freq.) by a simple method of transmitting interferring EM radiation by clicking or holding a light switch as close as possible between the off and on position so that the spark continually jumps the gap in the switch.
    (However, It doesn't seem to affect the new 'digital' TV frequencies)
    ..
     
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