By AA6J Bill Jeffrey
Assistant Scoutmaster and Merit Badge Counselor
6. Do I have do know a lot about electronics to get this merit badge?
You do not have to know a lot about electronics, science, or theory to earn this merit badge. You just have to learn a few major parts of the radio, draw some funny symbols, and learn what three electronic components do. Some very basic notes are given here. You may want to learn a little more about the three components you choose in part (d).
Do the following:
a. Explain the differences between a block diagram and a schematic diagram.
Block diagram: Shows parts of radio station.
Schematic diagram: Shows how electrical circuit works. It uses schematic symbols (see "d" below) to show the path of a circuit the way a map uses map symbols to show the path of travel on a hiking trail.
b. Draw a block diagram that includes a transceiver, amplifier, microphone, antenna, and feedline.
Remember what we talked about in requirement 4 above. Here we draw a kind of picture to show how it fits together.
c. Explain the differences between an open circuit, a closed circuit, and a short circuit.
An electrical circuit is made up of wires and various electrical components (see item "d" below) which together make up the electronic part of your electrical appliance, in this case a radio. There are 3 types of circuits:
Open circuit: No current flows - There is no electrical contact - For example, when a light switch is off
Closed circuit: Current flows correctly - For example, when a light switch is on
Short circuit: Current flows directly to the other side of the circuit - For example, a broken lamp cord where the insulation on the wires is broken so the two wires can touch each other - This is dangerous and can cause a fire. This will hopefully blow the fuse before it causes too much trouble, if the fuse is the right size.
d. Draw eight schematic symbols. Explain what three of the represented parts do. Find three electrical components to match to three of these symbols.
A schematic symbol is a picture which represents one of the (usually small) parts inside electronic equipment like radios. Here are some of the more common ones. You will have to find three actual parts yourself, maybe from a broken radio.
Fuse Contains a thin wire which is made to break which protects the rest of the circuit from damage if there is too much current, like from a short circuit. Battery Stores electric energy. Resistor Resists the flow of electric current, reducing its flow. Variable resistor Like a regular resistor, but adjustable. For example, the volume knob on your stereo. Earth ground A connection between the equipment (radio) and the earth, usually through a copper pipe driven into the soil. Chassis ground A connection of the negative side of the electronic circuit to the chassis, or steel frame, of the equipment. Capacitor Gets and stores an electric charge. Lets alternating current (AC - like in your house) flow but stops direct current (DC - like from a battery). Variable capacitor Same as a regular capacitor, but adjustable. NPN transistor Amplifies a current. PNP transistor Amplifies a current. Coil Also called a choke, it works the opposite of a capacitor. It lets DC flow but stops AC. Tube A vacuum tube made of glass with wire filaments inside. Amplifies a current. It has been replaced by transistors in most home equipment, but is still found in some high power radio transmitters. Antenna Sends radio frequency signals into the air. SPST switch Single-pole single-throw switch. Has two positions, on and off. Like most light switches DPDT switch Double-pole double-throw switch. A double-throw swithc has three positions. It can switch one input to one of two outputs - sort of like the switch you put on your television to switch between watching TV and playing your video game. The double-pole means it can switch a pair of inputs to either of two pairs of outputs.
|These notes are designed to help the Scout earn a merit badge that sometimes can seem a bit difficult. They are not intended to replace the Radio Merit Badge book.You will still need to meet with a merit badge counselor.|
6Links about this requirement below:
Copyright Bill Jeffrey 2000-2002. Rights to
reproduce and use for nonprofit purposes given.
Please do not copy this material to another web page. Thank you.
If you want to learn more about
Electronics has Electronic Circuits you might want to try, a Schematic Symbol Guide, How to Solder, Building Tips, and Electronic Calculators to take the math out of electronic formulas.
AC6V's DX & Amateur Radio - My friend Rod has the world's best collection of links to amateur radio information.
Last update February 3, 2002