Science Buddies: "Ask an Expert"

We're having some problems with our transmitter. First, the oscillator is supposed to be 10 mhz but the only signal we get is at 16 mhz (10 mhz where we live is also an active radio station). When we use the 16 mhz oscillator we don't find any signal. The signal that we do get is very weak, only about an inch from the antenna. We are using half of a speaker wire as the antenna so that might be an issue. Do we need to use a more substantial wire? Currently we are using 4 AA batteries for power. Our project was to see what difference the amount of power would make with the distance broadcast from the unit, but we haven't hooked up the 9V battery yet.

ramilner13 - The Science Buddies experiment calls for two crystal oscillators, a 1.0MHz and a 1.2288 MHz device. These are within the AM broadcast bands in the US and most foreign countries. You describe a 10 MHz oscillator, did you mean 1.0 MHz? It's possible that if you have a 1.0 MHz (1000KHz) commercial station in your area that might cause a problem for your experiment assuming a 1.0 MHz oscillator is used. I don't know why you seem to receive a signal that is 1.6 times to oscillator frequency. That would not be an expected harmonic. Please verify the frequency of the crystal oscillator you are using, check the wiring of the setup, and the transformer connection such that the impedences are correct. The type of antenna wire is not critical, and at these frequencies, can be relatively long, for example a random length 3-10 feet long. Good luck.

Rick Marz

Thanks. I get my hertzes mixed up. It is a 1 MHz oscillator. The second oscillator was ordered using the materials list from the project. It appears to be a 1.6 rather than the 1.2288. I'm happy to hear that an expert can't figure out why we get a signal at 1.6 from the 1 MHz oscillator. We'll get a longer wire and see if that helps our range.

Hi Rick - I found Science Buddies through a Google search after discovering that the little wooden box with all the doo-hickies that I played with as a kid was my grandfather's crystal radio. I was wondering how difficult it might be to get this set (it is a wooden box, really, with a dial, four contacts and the castswiskers arm) operating again. From what I've learned, there is supposed to be a crystal of some sort beneath the catswiskers (which appears to be missing), and the contacts are labelled G, A, T, & T (ground, antenna, earphones, and something else?). I would appreciate greatly any advice on this project and any guidance on moving forward with it. Thanks! Brian

Hi bhartig,

It sounds like you had a fun little project on your hands! Unfortunately, these forums are specifically for K-12 students, parents, and teachers working on science fair projects. It sounds like your project doesn't fit into that category. However, a different set of online forums might be able to help you. Good luck!