My daughter and I built a crystal radio recently. We used more or less the same design that I’d used a few years ago when constructing a radio. With this one, we had a really good ground and a pretty good antenna. Those seemed to help a lot.
So far, we’ve only be able to tune in one station but it is very loud and clear. I was able to tune in three or four stations on the previous radio I built, but that was in another city, and they were not nearly as loud.
We experimented a bit and found we could get the same station without tying into the ground or antenna. We tried clipping the antenna to a lamp in the room, and that noticeably increased reception and volume.
We’re thinking about adding a smaller second coil that is connected to the antenna. I learned about that technique while reading and watching videos about crystal radios. It seems that might help allow the radio to tune in more than one station, and there is room on the cylinder we used for the coil.
My daughter was pretty excited when the radio actually worked and she could hear the country-western song in the earpiece!
For this particular radio, we used an empty Metamucil container for the cylinder (roughly 3″ in diameter), 22 AWG magnet wire, a brass rod for the tuning wiper, a high-impedance earphone, and scrap wire from various sources for the wiring, antenna, and ground wire. For the diode, we used a 1N34A germanium diode. We added an optional 47K ohm resistor. We were able to order the magnet wire, brass rod, earpiece, diode, and resistor inexpensively online. Screws, some of the washers, the pine base, and miscellaneous wire was salvaged here and there. I did pick up a handful of brass washers at the hardware store. We also used a couple of alligator clips to make attaching to the antenna and ground wires quick and easy.
My daughter sanded the surface of the end of a length of rebar that’s driven into the ground in the front-yard to hold in place some landscape edging. We connected the ground-wire to the rebar. The antennae, like the ground wire, is several sections spliced together of insulated braided copper wire that I salvaged from various electrical plugs, as well as a few lengths of solid copper wiring. I found an old, home-made antennae when I moved in…it a 2X4 piece of pine screwed onto a rectangular plywood base. There are two lengths of copper wire running parallel with the 2X4 and bent into zigzag shapes. I think originally it was someone’s DIY television antennae. There was a coaxial connection tied in to the copper wiring, which we removed. We connected our antennae to the copper wires and set it on our truck bed.
Minimal tools were used. My daughter cut the pine board with an old handsaw; we used a manual pin vise for screw holes; a screwdriver to drive screws; a wire cutter/stripper for working with the various gauges of wire we used; some electrical tape for covering our splices; a hot-glue gun to affix the cylinder to the base; a needle nose pliers to help twist wire around screws; a hobby knife (like an exacto) to drill out little holes in the plastic cylinder to run the magnet wire through; and a little sanding board I use for models to sand the rebar and to sand of the thin enamel on the magnet wire at the appropriate places (because we didn’t have any sandpaper on hand).
Click here for some basic instructions to build this radio
Crystal radio II update:
We decided to add a second coil, using the same gauge magnet wire (the wire has a different color coating, but is the same size). We added a second tuning wiper for this coil and changed the wiring of the radio a bit, so that one tuner is wired to the ground and one to the antenna. Now one wiper can be used to tune the large coil and search for stations, while the second wiper can be used to fiddle with the antenna (that’s a technical term!). Using both wipers together seems to help pick up additional stations. There is one very strong station, however, that seems to drown out most other signals. It was for this reason that we tried the second antenna tuner. I think it helps a little, but not as much as I was hoping.
Also, my daughter and her friends wired in more earpieces, so they could all listen at the same time. It worked very well! At one point, they had three pieces wired in at once, although now there are only two.
