Any radio, television or other electronic form of long distance communication is based on the principle of resonance. Just as a tuning fork when struck can cause vibration in a second tuning fork of the same pitch, a broadcasting antenna will cause resonance in a receiving antenna set for the same frequency or pitch. Make a simple receiving antenna which can receive a range of frequencies by adjusting its electronic resonance through a use of fixed inductance and variable capacitance.
Instructions
1. Cut a five foot length of flat antenna wire, stripping one end and soldering those bared wires together, then doing the same at the other end. Ideally, you know the frequency range of the radio, television, or other signal you wish to tune to. The best antenna would be the same wavelength as the signal, but this is rarely practical. For our example, a five foot antenna would be a good half wave receiver for a 100MHz (mid-band FM radio) signal. A higher frequency (shorter wavelength) signal like a television signal would require less antenna and a lower frequency like AM radio would do better with a longer antenna.
2. Cut one side of the flat antenna wire (not completely through where both conductors have been cut) at the middle of antenna wire. Strip one inch of insulation from the wire to each side of the cut.
3. Cut a wedge from ten of the fender washers approximately 1/3 of the circumference (picture a pie with 1/3 cut out).
4. Solder one of the cut washers onto one of the rods at a point one inch from the end. Be sure to have the washer perpendicular to the shaft. Solder the next washer 1/4 inch further down the shaft and parallel to the first washer, with the cut segments aligned. Continue until all of the cut washers are mounted along the shaft like teeth on a comb and all of the cut segments are in the same position.
5. Repeat step 4 using the uncut washers along the second shaft. Verify the two completed assemblies are able to interlace without any of the washers (plates) touching.
6. Drill a pair of holes in front and back of the 6 inch side of the plastic box to allow the rod with the uncut washers to be mounted without the washers touching the bottom of the box.
7. Strip the ends from a four foot (or any convenient length) of insulated wire, soldering one end to the mounted rod and the other end to one of the bared wire ends at the cut in the antenna.
8. Drill two more holes in the box where the second shaft can be mounted with the washers interleaving with, but not touching the washers on the first shaft. Mount the second shaft as close as is practical without any metal touching other metal. The first rod can be stationary, but the rod with the cut washers must be able to rotate.
9. Solder a second piece of insulated wire from the second shaft to the other side of the cut in the antenna. You should now be able to rotate the second metal rod where some, all or none of the cut section can be interleaved with the washers of the first shaft. The greater the area of metal overlapping metal as you turn the rod with the cut washers, the greater the capacitance between the washers (plates). This is effectively a variable capacitor, allowing you a degree of tuning against the fixed inductance of your antenna.
10. Using insulated wires, connect your radio to the ends of the capacitor rods and tune for your desired frequency.
Tags: second shaft, with washers, antenna wire, able rotate, antenna would, first shaft, five foot