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Using a low power amateur radio transmitter and a simple light bulb receiver circuit, we see how radio waves and electromagnetic induction transmit energy and signals wirelessly through the air. We also see how dipole and Yagi antennas radiate their energy in different patterns. Read on to build your own dipole receiving antenna!

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LightBulbEMF1.jpg

I made the light bulb detector with some materials I had laying around my apartment: a flash light bulb, a chopstick (wooden dowel), wire, tools to solder, hair ties (zip ties work too). You can easily make one too. But make sure that you comply with all safety regulations when you play with your light bulb detector. More information on RF exposure
safety is available here.

LightBulbEMF3.jpg

1. Solder small pieces of wire to the terminals of the light bulb.

2. Basically you are using wire to make a dipole antenna for the light bulb. Use this calculator to find the length of the wires for your dipole antenna by entering in the frequency. The value for the quarter wavelength is the length of each wire (you may need to cut off an additional half inch from each side).

LightBulbEMF4.jpg

3. Solder the antenna wire to the light bulb wires and secure everything to the chopstick to keep it straight using your hair ties/zip ties/glue gun.

dianaeng

dianaeng

Fashion + Technology
Diana was a contestant on Project Runway season 2, graduated from RISD, and currently lives in New York City.


  • screaminscott

    What a great learning tool!

    Can anyone direct me to a web site that has a visual representation of how the reflector and director wires work? It seems counter-intuitive that a simple wire could reflect or focus the electromagnetic energy.

  • Qenton

    I love when something is explained simply.

    Explains why all those ham radio towers my neighbors had were shaped the way they were.

  • amasci.com

    > direct me to a web site

    I wish someone would make such animations! The only visual representations I’ve seen have been for single-element antennas. MIT 802 course (TEAL project) has some good ones:

    http://web.mit.edu/8.02t/www/802TEAL3D/visualizations/light/

    Antennas are very strange beasts, but it’s not impossible to arrive at an intuitive grasp. One important point is that antennas act “fuzzy,” they don’t act as thin or as small as their physical size. A narrow wire antenna can absorb waves which pass to the side and don’t actually touch the metal, so the antenna casts a wide “EM shadow” which acts like a broad disk rather than like a thin wire. Think of antenna elements as being like fuzzy spheres of 1/2-wave diameter.

    Another important point is that all antennas receive and transmit simultaneously. Therefore, if you hold a disconnected metal wire near a transmitting antenna, that floating wire absorbs EM waves, develops an internal current, begins oscillating, and transmits the waves again… but with a phase-lag. You can adjust the phase-lag of the re-emission by changing the length of the wire. A Yagi antenna is actually a row of separate radio transmitters, each one sending out waves of slightly different phase. “Sculpt” the phases so they add and subtract just right, and you’ll end up sending an intense beam from one end of the array (yes, very analogous to a row of atoms in a laser rod.)

  • amasci.com

    Hey, try using a #48 or #49 pilot light. Those things turn on at extremely low mA. (But wouldn’t a red superbright LED be even more sensitive?)

    • Aaron Propst

      an LED wouldn’t light with an AC source. current can only flow one direction through them.

      • Derp

        surely it would light half the time?

  • http://david.rysdam.org/blog/

    I didn’t realize all those antenna “crossbars” were reflectors and lenses. A longer video would be really cool. Maybe a fixed array of lights to really show how changes affect things?

  • panicopticon

    Diana,

    I’ve looked at a bunch of your ham posts here on Make and was wondering what sort of flexible HT antennas you like?

    Thanks,
    Panic

  • ATT

    I’ve had a basic understanding of antenna theory for quite a while, but you just hit a home run in the world series at the bottom of the ninth with the bases loaded. Thank you.
    It was truly magical watching your demo.

  • Chiz Chikwendu

    instead of an amateur radio transmitter, can I use a walkie talkie radio transmitter to transmit radio waves which can be detected with light bulb antenna?
    Can I use a regular 22AWG stranded copper wire to make the antenna?
    Is 0.5Watt transmitterĀ output power too low?

  • http://jf1nlh.web.fc2.com Silva

    Grate…..

  • Art

    Hey Girl!!!! You rock!!! A very neat and concise visual explanation. You are a great teacher! Thank you! Art

  • YeahSure

    Does anyone else besides me think that geeky young asian girls are smoking hot?

  • the invantor

    can you use any transmeter

  • http://youtube bob m.

    diana, you are a cute geek and the video is informative, but longer or something would help more,maybe elaborate in another video.

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