SHORTWAVE RADIO

OBJECTIVE:

The objective of this project is to understand the basics of constructing electronic circuits and how sound waves are transmitted and received over great distances.

SKILLS LEARNED:
How to solder
How to read and interpret drawings of circuits and the symbols which represent each piece.
How to strip and prepare wire for use.

TIME:             Eight hours or less

INSTRUCTOR NEEDS:

One instructor per three participants (needs will vary depending on ages of participants.) It would be very beneficial if the instructors have a working knowledge of electronic circuits.

PARTS LIST:
Project box (plastic) or other container (cigar box, pencil box, etc.) must be non-conductive
SPST switch
2/9 volt batteries
1/8-ohm speaker
35 mm film canister
Double-sided tape
6' 30 AWG magnetic wire
6" stiff wire (clothes hanger)
Capacitors: 1 uF
                10-365 pF (variable)
                10 uF
                100 uF
Resistors: 2 1 kohm
                100 kohm
                10 kohm
Op Amps         386
                  741 
2/9 volt battery clip 
PC Board
Wire
1 screw 1/4" x 1/2"
Potentiometer

TOOLS AND SUPPLIES:
Soldering iron
Solder
Drill, standard size bits
glue gun, glue sticks
wire stripper/cutter
sandpaper

ASSEMBLY PROCEDURES:

1. Provide each of the participants with the parts listed above. Note: Make sure that the capacitors and resistors given to the participants are of the required value. It might be easier on  the instructor if the smaller parts were placed and sealed into a sandwich bag until needed by  the participant.
   
   
2. Take the film canister and wrap the outside with the double-sided tape. Then begin at one end of the canister to coil the magnet wire around it being careful and patient so that each winding touches the one made before it. Leave at least three inches of wire unattached on either end. This will be the coil of the tuner (4 in the schematic).
   
   
3. Apply the sandpaper to the coil, removing the lacquer from a small strip of the wire from the top to the bottom of the canister. The lacquer should remain on the position of each windingwhich is touching another, to prevent a short circuit, but only bare wire should be visible along the sanded strip. This "cleaned" portion will be the contact area of the coil. Now, drill a smal hole in the bottom of the canister and push the extra wire left at the top through it.
   
   
4. Now, using the hot glue gun, attach the canister to the center of the lid of the project box. CAUTION: The hot glue guns are HOT! Note: Be careful that the contact area is exposed on the upper surface and that no glue is applied to it. The contact area should be approximately a 45 degree angle to the lid of the project box.
   
   
5. While the glue holding the coil is drying, begin arranging the circuit pieces on the work table as shown in the schematic. Use the leads on each piece to "connect" with those of the other pieces by just touching them together so, from the top view, the schematic has been recreated. Save the operational amplifiers until last because they do not look like their figure in the schematic.
   
   
6. If a printed circuit board is used, as recommended, use the long metal strips which boarder the board to reference the high and ground sides of the circuit. It is important that the participants keep track of which boarder strip is considered their high side and which is the ground side.
   
   
7. Once the high and low sides have been determined, the circuit pieces can be placed on the  board. Do not solder or cut any of the pieces until all of the pieces have been placed. Pay careful attention to the metallic strips on the back of the board. They will replace the wires  which were once used to build this type of radio. If one piece is not supposed to be connected to another, make sure that their leads are not in holes corresponding to the same metal strip.
   
   
8. Once all of the pieces are in place and room is left for the op amps, each lead should be trimmed so that a small portion protrudes from the board and is soldered to its metal strip. BE CAREFUL; the soldering iron may be very hot! Be sure to clean the iron with a sponge or paper towel and then "tin" the tip with a small amount of solder. After tinning the tip, heat the metal strip to be connected with the iron and apply a small amount of solder to form a bead on the strip. The bead should not extend past the edges of the strip. CAUTION: It is extremely important that the soldering be neat and no "solder bridges" exist between any two strips unless connecting a piece to the high or ground strips. After the bead is formed, push the lead beingconnected through the hole until it is stopped by the bead. Then, just heat the bead again and,while maintaining the heat, push the lead the remainder of the way in.
   
   
9. After connecting the speaker and all of the pieces to the board, use the instructions for the op amp to locate the pins which correspond to the numbers on the schematic. Place the operational amplifiers on the board so that the pins can be soldered to the appropriate strip and then solder the pins as was done for the other pieces. It may be necessary to use "jum wires" which connect pieces which are located far away from each other or are positioned so that their leads cannot be connected by a common metal strip.
   
   
10. By now, the coil should be pretty well affixed to the lid of the box. If not, wait until it is. Drill  three holes in the lid of the box beside the bottom of the canister. The one closest to the   canister should be just large enough to fit the two coil leads through. The second hole should be about an inch from the canister and should be big enough so that the top part of the switch can fit through it. The third hole should be placed on the opposite side of the canister from the hole for the switch. This should be large enough to accomodate the potentiometer which is the  volume control. Mount the switch to the top of the box and solder it to the strip which corresponds to the battery lead as shown on the schematic. Now solder a jumber wire from the other terminal of the switch back to the board. Connect the potentiometer to the boar using jumper wires in a similar fashion. Then solder the coil leads to the board as shown in the schematic.
    
    
11. Now , drill a pilot hole smaller than the screw about one quarter of the distance form the edge between the edge of the lid and the coil on the side of the coil of the contact area. Then take the piece of stiff wire and bend it around the screw so that a loop is formed which will hold the wire in place. This will be the tuning side. The lenth of the wire will depend on the size of the box lid but care should be taken such that it stays in contact with the contact area as it is moved side to side. The tail of the tunner should be connected to ground as well. Another hole may need to be drilled in the box to accomplish this.
    
    
12. The antennae can be a piece of insulated wire 10' or longer or one which has been commercially produced. In either case, a hole should be drilled in the side of the box and the antennae lead should be fed through the hole and soldered to the appropriate place on the board. A hold should also be drilled for the ground wire. I t is very important that a good connection be made beteween the radio and the ground so that good signal reception can be maintained.
    
    
13. After these steps have been completed, the PC board can be mounted to the box, using the standoff and bolts. The battery can then be connected and the lid can be put in place.