RSS for MAKE
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!
Subscribe to the MAKE podcast in iTunes, or download the m4v video.
More:
- Ham radio fun for holiday air travel
- How-To: Make a Star Trek Bluetooth Communicator
- How-To: Set up an HF portable radio while hiking
- Ham Radio 101: Getting Started Without a License
- Catching satellites on ham radio
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.
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).
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.
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.
I love when something is explained simply.
Explains why all those ham radio towers my neighbors had were shaped the way they were.
> 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.)
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?)
an LED wouldn’t light with an AC source. current can only flow one direction through them.
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?
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
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.
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 transmitter output power too low?
Follow MAKE
Maker Shed: Deal of the Day
On Sale: $79.99
DIY Hologram Kit
Make your own holograms! Just set up the included jig, use the laser to illuminate your object, and expose the self developing film. You'll have your very own high quality hologram in less than an hour!
Read More →