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The purpose of this part of the web page is two part. One to explain how to construct a simple crystal radio and two to explain the mechanics of how a radio works around the construction of this radio. This explanation of how a radio works will not be detailed, but somewhat simplified, so that a person with little science background can understand the "magic" of radio.
Construction of a Crystal Receiver Assembling the Radio
In the process of constructing the crystal receiver refer to figure 1 for guidance when reading through the instructions. The parts on this drawing are labeled according to the numbers listed previously in the parts list. Also, for those individuals with more electronics background, there is schematic diagram (figure 2) which can also be used to construct the radio.
First take your wooden dowel and drill a small hole about a 1/2" from each end. Make sure each hole is drilled in the same direction. Then insert the #26 enameled wire in a hole on one end, so about 4" is protruding through. Then begin winding the remainder of the wire around the dowel until you reach the other hole. Make sure when you wind the wire that it is kept close, tight and no gaps are present between the two holes. When you reach the other hole, insert the wire through it, and again leave 4" protruding before you cut it off. The two 4" protrusions of wire are where you will make your connection of the coil to the rest of the circuit. Next take your two tin-can strips and nail the top half of each strip to the dowel on each end of the core, and nail the bottom half of each strip to the base board. The strips should be nailed to the base board so the core is centered and about 1 1/2" to 2" from the top of your base board. Two nails go into the core and one into the base board for each strip. The strips will also need to be bent at 90 degrees to accomplish this. Now that the core is made and attached the base board we will now go through the process of making the slider arm.
Bend the 5" by 3/8" metal strip as show in figure 3. A thick piece of bare copper wire will have to be soldered to the underside of the front. The copper wire helps make a good contact between the coil and the slider arm. You may want to use your #26 enameled wire for this but make sure you sandpaper the enamel off the wire before you solder it in place. The purpose for the copper wire is to only make contact with one or two turns of the wire on the coil when you move the slider arm across it to tune in your radio station. When the solder has cooled wrap some electrical tape across the top edge of it (part not touching the tuning coil) to prevent you from weakening the signal when touching it. On the other end of the sliding arm drill a hole big enough so the screws you purchased will barely fit in it. The slider arm should now be complete and ready to be put on the base board with the other components.
Looking back to figure 1 lets now put the parts together as shown by the drawing.
Make sure when putting the pieces in their proper places that good electrical connections are made. This means that the enamel is sanded off the last 1/4 to 1/2 " of each protruded end of the tuning coil, the ends of the electrical wires are stripped the same amount as the enamel sanded off the coil wire, and the washers when screwed down into base board make adequate contact with bare wire and the other parts they are connecting. Another way to get even better connections where the washers are is to solder these places together instead of having the metal in the washers complete the circuit. The washers would be obsolete if this process were used. Notice in figure 1 that where the screws go into the Fahnestock clips the wire or part that is connected here must go between the clip and the screw, not between the clip and the wood. When using the Fahnestock clips to connect the ground, antenna, or headphones make sure the ends of each has bare wire exposed before inserting them in the clips. One last question that might arise when assembling the radio receiver is; "Does it make a difference which way I put in the capacitor or crystal detector?" The answer to this is "No", just make sure the leads on the ends of each make good connections whether by washer or solder. You should now have a Crystal radio receiver that is almost ready for use.
The last things to do before trying your receiver out are to; file off the enamel on your tuning coil where the copper wire on the sliding arm makes contact with it, connect your ground and antenna, and attach the headphones. Make sure when filing off the enamel on the coil that you only take off enough for a connection to be made. note that the sliding arm makes a curved path when going across the coil so try to follow that path when removing the enamel. The copper wire on the sliding arm will remove the enamel itself if taken across the coil enough times with a little pressure. If you choose to try removing it in this manner, make sure you remove any enamel that might accumulate on the sliding arm copper wire after doing this. Remember bare wire must meet here if the tuning coil is to work properly.
When hooking up the ground the easiest way to do this is to run some wire from the ground connection on the radio receiver to a water pipe. If inside the house just wrap the bare end of your ground wire to any cold water pipe under a sink or if outside connect it right to a faucet, or a 3 to 4' metal stake or pipe pounded into the ground. Any metal that has direct access into the earth can be used to ground your radio. One word of caution, make sure there is no direct source of electricity being supplied to the ground connection you have chosen.
Getting a good antenna is probably the most important part of the successful completion of your radio receiver. Without the proper hookups, the sounds you are listening for will not appear. When erecting your antenna make sure you use only 50 to 100' of wire. It does not matter whether it is insulated or not, but if uninsulated wire is used the ends of the wire must be kept from grounding by putting insulators on the ends before they are connected to a structure. Figure 4 shows some different insulators that can be used and figure 5 shows where they should be attached on the antenna. If insulated wire is used for your antenna these will not be needed. Note that if insulated wire is used you will have to strip the wire on the antenna where you connect the lead-in wire from your radio receiver. Only strip enough wire to connect the lead-in to bare wire, do not do this to close to the end or you loose the insulating effect of the antenna already there. Make sure the lead-in wire that connects the radio receiver is insulated wire also.
When putting up the antenna itself figure 6 shows some places where it can be installed. Again be cautious when attempting this feat especially if climbing trees or building when doing it. The closer to 100' of antenna and the higher it is the better your reception will be. Lastly remember: NEVER USE A POLE SUPPORTING ELECTRICAL WIRES AS AN ANTENNA SUPPORT. DO NOT STRING THE ANTENNA SO IT CAN FALL ON ELECTRICAL POWER LINES OR SO THEY CAN FALL ON IT. AND ABSOLUTELY DO NOT USE ELECTRICAL POWER LINES AS THE ANTENNA FOR YOUR RADIO RECEIVER. Following these simple rules could easily save you from injury or death.
Your radio receiver should now be complete, hookup your headphones move the slide arm and see what stations you can pull-in through your receiver.
