Science Buddies: "Ask an Expert"

My son and I are doing the crystal radio project, just a bit tweaked though. The coil is 93 turns 3.25 inch around by 2.25 inches long, with an unidentified glass diode with a forward voltage reading of 0.523 and a 100 pF ceramic capacitor. We are using a Bluetooth speaker fed with an aux cord from the headset connection. We are using an off center fed dipole, just using the long side for the antenna connection. Here's the part I don't understand. We barely heard anything while tuning up and down the could, so I was going to swap the antenna and ground and see if that changed anything, and boy did it....I took the ground off first and the radio came to life! Sounds like a factory radio! I thought you had to have a ground for a crystal radio to work, yet ours works great without it. Why?

Hi JasonB0020,

I'm assuming that you're working on the project described here:

https://www.sciencebuddies.org/science- ... stal-radio

Based on my (limited) understanding I think the crystal radio circuit needs to be grounded. Perhaps your original circuit was grounded at two points, resulting in a ground loop that interfered with the radio. Is it possible that the connection with the Bluetooth speaker is providing a ground?

I hope this helps. Please ask again if you have more questions.

A. Norman