Radio Lab
Additional Information

1. For drilling holes in wooden bases for woodscrews an electric drill is needed.

This amount equipment is sufficient for a group of 24 students.

Equipment	Notes
1 Electric Drill	Cordless drill is convenient, with reserve battery charged.
3 7/32 inch bit	Fits #6 wood screw, extras needed in case of breakage.
2 pr Safety glasses
1 Drilling Template	Facilitates quick drilling
1 piece of scrap wood	Helps to prevent drilling into the floor or table top.

2. A piece of scrap cardboard to use as a sanding surface helps to prevent scratching and scuffing of the table top when sanding insulation from the wire.
3. When winding the coil it is not necessary to get each turn perfectly flat next to the preceding turn, some overlap is tolerable.
4. Occasionally the wire may break when winding the coil. It is not necessary to rewind the coil from the beginning. It is possible to solder the wire back together. Remove the insulation from the end of wire on the coil and the wire on a spool. Solder them together side-by-side. Tape or insulation is not necessary since the other turns are insulated. Continue winding the coil.

This repair requires a soldering iron and solder.

5. When working with a group, it is optimal for each person to have his or her own spool of wire from which to wind the coil. If this requires too large an initial expenditure, it is possible to have two people share a spool. In this case one person winds the coil while the other spools out the wire. When one coil is completed the spool is switched. Sharing beyond two people is not recommended as the time for each person to complete the project becomes very long.
6. The project can be completed in as little as time as 45 minutes. A typical time to completion is 75 to 90 minutes. Winding the coil takes the most time.
7. Common problems and troubleshooting. If the radio does not work, the following are some common problems to consider.
• A poor or nonexistant connection to ground. Use a good ground such as an outdoor faucet, make sure there is an electrical connection between the ground wire and the grounding object. The grounding object might be electrically insulated with paint, rust, or another material.
• Loose or disconnected wires.
• Insufficient removal of insulation from the coil wire.
• Antenna too short. In some cases reception can be improved with a longer or higher antenna.
• Non-functioning earphone. Rare but it does happen on occasion.
8. Tunable Radio. It is possible to make the radio tunable by adding a variable capacitor of 5 - 266 pF as shown in the accompanying schematic in Figure 1. This is generally not a very satisfying result. The ability to tune is marginal. Usually the number of strong AM signals from which to choose is small.
9. Amplified Radio. The radio works well with an audio amplifier. Figure 2 shows a schematic of an amplification circuit based on a 741 op Amp and a 386 audio power amplifier. This amplifier is useful when verifying the proper operation the radio.