Coil

The coil and variable capacitor designs are a celebration of mathematical art and function. A sturdy 30-gauge magnetic wire is wrapped onto a 4" length 1.5" diameter clear plastic rod to effect 1000uH.

Variable Capacitor

A middle triangle metal piece interweaves between two other pieces. A 0.25" diameter 0.25" length nib magnet "sandwiches" the two aluminum triangles from the attraction given by the far end steel triangle. Given the formula for capacitance = (permitivity constant of space) * (media dialectric constant) * Area / distance, the capacitance is maximized when the distance between the plates is minimized. Surprisingly, the best dialectric media turned out to be clear plastic tape used in everyday packaging. Swinging the triangle produces a variable capacitance from 29pf onto 311pf. It is capable of producing 367pf with the current triangular dimensions.

Snap the extended twisted wire to the variable capacitor point.

Detector Stage

Snap the 1N34A crystal diode, 0.33uf coupling capacitor, and diagonal 75K ohm rods with the extended nib magnet meeting the detector diode onto the simple panel. Assure the cell isolators (in blue) electrically isolate the crystal diode on both sides of the simple panel. Attach the antenna aligator clip wire.

Output Stage

Snap the earpiece and 1uf decoupling capacitor on the remaining side of the simple panel. Note the cell isolators (in blue) extend to both sides.

Amplifier Stage

Snap the 7.5M ohm bias and 150K ohm resistors onto the 2N4401 transistor panel.

Attach Amplifier

Note the 1uf coupling capacitor feeds a signal to the transistor base. A third cell isolator is placed.

Mount the coil base (with coil atop) onto the cube. Assure all connections are secure and then connect the battery.

Final Assembly

Position the stacked panels. The aligator clip can be fastened to a free-standing piece of metal such as a bookshelf rail.

At this point you are ready to listen to radio stations! Try different locations to get the best signal - outdoors gets the strongest signals. You may also touch the other end of the variable capacitor to effectivly make your body a "ground" and increase the signal strength.