FAQ for Crystal Radio Project

Questions about "Build Your Own Crystal Radio" project and kit. (http://www.sciencebuddies.org/science-f ... l?from=AAE)

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FAQ for Crystal Radio Project

Postby amyc » Fri Jan 20, 2012 10:35 am

The following FAQ contains frequently asked questions and answers about the Crystal Radio project. If you are having trouble with the procedure, you may find assistance in the answers below.

Q: Is the microammeter necessary to use so this radio can function?
A: No. The experiment says that the multimeter or microammeter and voltmeter are optional, so these are not necessary for the radio to function.

Q: I am not picking up any sounds. What should I do?
A: This radio will only pick up AM stations, and in some areas there are very few AM stations left. To search your area for AM stations, check out this website: http://www.fcc.gov/encyclopedia/am-query-broadcast-station-search.

In addition, you can try stretching the long-wire antenna in a direction perpendicular to the direction where the AM broadcast station antenna is located in order to pick up the maximum signal strength. Keep in mind that you'll need a very good antenna! You can try clipping a wire lead to a long wire antenna run between two objects that do not conduct electric signals, like trees for instance, to see if you can pick up any signal. See the Project Idea (http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p014.shtml?from=AAE) for more information on the antenna.

Finally, try tuning the crystal radio at night when the signals from distant stations are more likely to be strong enough.

Q: I followed all the procedures, but I still cannot get my radio to work. What can I do?
A: There are few things you can double-check in order to troubleshoot your radio:

  • Check your radio for open circuits (e.g., connections between parts are not being made, broken wires, etc.).
  • Check your radio for short circuits (e.g., things touching that shouldn't or perhaps you built your radio on a base that has absorbed moisture or is otherwise conductive).

Q: My wire is not insulated. Could this cause a problem?
A: Yes, this definitely could cause a problem because the loops of the coil need to be separated to prevent a "short circuit," and if you do not have insulation, this separation might be lost. You should use either regular insulated wire with a plastic sheath or "magnet wire" which has an enamel coating to insulate it.

Q: Do I need a ground wire?
A: Yes! You actually need a very good ground for this type of radio to work. You can attach a wire lead for the ground to a metal water pipe. Plastic pipes will not work. Alternatively, you can connect a wire lead to a metal rod that is pounded at least 2 ft. into the ground.

Q: Where do I connect the antenna on a crystal radio?
A: The basic AM radio has four parts: antenna, tuner, detector, and reproducer. In the crystal radio, the antenna length acts as a tuner, the diode is the detector, and the earphone is the reproducer. With those parts, how they are connected almost does not matter, you only have two choices, diode and earphone in series or in parallel, with the antenna and ground connected to the combination.

Q: Will my radio work?
A: This radio works and will receive nearby AM signals. The loudest station will be faint and probably the only one. A nearby TV station will sound like a 60 Hertz buzz caused by the video signal. Nearby airport and airplane radar will sound like a buzz at some other (higher) frequency. FM stations will not be heard at all.

Q: How do you tune a crystal radio?
A: There are a few ways to tune the radio to a particular frequency, such as adjusting the length of the antenna wire, or adding a capacitor to the radio.

Here is a link that may help:

http://www.midnightscience.com/howxtal.html

Q: What about capacitators to improve performance?
A: If you want to use capacitors, get a selection of small capacitors in the range of 100pf to 1500pf and connect them one-at-a-time across the coil (between the top and the bottom leads of the coil). You should hear a louder signal when you get close to the correct value. Fine tune by doing one of several things:

  • Add one of the smaller capacitors in parallel with the prior capacitor. If it gets better, try the next larger one. Select the best combination based on how loud the signal is.
  • Use the biggest capacitor and move down the coil one tap at a time to tune for the loudest result.

Basically, what you are doing here is adjusting the resonant frequency of the coil and capacitor to match the station's frequency.

Q: Is there an alternative to the taps on the coil?
A: Yes. You can build the coil using magnet wire, which is wire insulated with enamel. Wind the magnet wire on the paper tube, glue it in place and then sandpaper the enamel insulation off along a single narrow strip perpendicular to the coils. Then make a slider from a piece of metal that can make contact at various points along the coil and build a means to hold it in place – this makes up the tuner portion.

Image

(Image credit: By Hihiman (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons, http://upload.wikimedia.org/wikipedia/commons/b/b1/D_1925_Jahnke_Schiebspulendetektor.jpg)


If you have other questions about the procedure or need assistance troubleshooting your Crystal Radio project, please post your question in the forum for this kit at Ask an Expert: http://www.sciencebuddies.org/science-fair-projects/phpBB3/viewforum.php?f=57. Our team of volunteer Experts is available to assist. We attempt to reply to questions within 24 hours. Please note that you will need a free Ask an Expert account in order to post questions.
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