Radio Study Guide

Use this guide to study for the simulated amateur license exam. The test will have ten questions. You must score at least 70% correct to pass. You can consult this guide while you take our test (unlike the real exam).

1.

Law

Radio signals can travel around the world. To avoid interference, international treaties define when, were and how radio transmitters can be operated. In the United States, the Federal Communications Commission (FCC) regulates transmitters, under direction of the US Congress. Treaties reserve many frequencies for personal, non-commercial, two-way communication. 
bands These are known as the amateur bands. Here are some examples:
Band: 40 meters
Use: local by day, long distance at night
Code: 7.000 to 7.150 MHz
Voice: 7.150 to 7.300 MHz

Band: 20 meters
Use: long distance by day
Code: 14.000 to 14.150 MHz
Voice: 14.150 to 14.350 MHz

Notice that code and voice do not mix together well so separate frequencies are allocated to each. 
rules The FCC issues licenses to transmit in amateur bands to people who have demonstrated that they know the laws and have the skill to obey them. Other laws an amateur must know include:
  • Transmitter power must not exceed 1000 watts.
  • Tall antennas are not allowed near airports.
  • Operators must not use bad language.
  • Messages cannot be in secret code.
  • Amateurs cannot transmit music.
tests To get a license one must fill out an application (form 610) and pass an FCC test. The FCC allows volunteer examiners (VE) to give the test, but require that they do so in teams to discourage cheating. 
help  The American Radio Relay League (ARRL) is a non-profit organization that suggests many other ways that amateur radio operators can get along, have fun and provide community service. They also publish study guides for the FCC exam and will help students find VEs. (See http://www.arrl.org)

2.

Operating

An amateur license includes a station call sign involving letters and numbers. W1AW is an amateur licence. The W1 means Northeastern United States. So would K1 and a few other prefixes. Some are logical, like J for Japan or F for France. 
identify Amateurs are required to identify their station at the beginning and ending of each contact, and every 10 minutes in the middle. Normally one says:
"This is K7XYZ", or
"W1ABC this is K7XYZ"
In the second case, the station, K7XYZ, is also identifying the station that it is communicating with, W1ABC. Amateurs looking for someone to talk to will use the abbreviation "CQ" to mean "calling anyone". They will say:
"CQ CQ CQ this is K7XYZ  K7XYZ  K7XYZ"
repeating themselves for clarity.
q-signals Amateurs use a variety of telegraphy abbreviations including the three-letter Q-signals which stand for common questions or commands. For example:
QTH means location, as in "what is your QTH?".
QSY means change frequency, as in "let's QSY up 5 KHz".
QRX means stand by, as in "QRX one minute".
QSL means received ok, as in "QSL your last message".
logging Amateurs keep a log of their station operations. The FCC can inspect a station's log and expects them to include dates and times of operations and  type and power level of transmissions. Traditionally amateurs also record the names and locations of the stations they contact and a report of the strength and quality of each other's  signals.

3.

Theory

Amateurs can build transmitters from parts and transmit with them without asking for special permission. (All other transmitters, be they cell phones or tv stations, must have their designs "type approved" by the FCC.) Consequently amateurs must know some theory to keep their stations working well.
frequency A rapidly alternating current will induce radio waves in free space. Depending on the frequency of alternation, these waves can reflect off of the ionosphere and skip around the world. The frequencies that skip best are between 3 and 30 MHz, the so-called, short waves.
wavelength Shortwave frequencies are measured in megahertz (MHz). A 3 MHz signal completes 3 cycles in a microsecond, a 30 MHz signal completes 30 cycles in the same time. Radio waves travel 300 meters in a microsecond, same as light. A 30 MHz signal will travel 1/30 x 300 = 10 meters in one cycle. We say its wave length is 10 meters. Frequency F and wavelength L are related by the formula:
L = 300 / F   or   F = 300 / L
Try this formula with the band frequencies from section 1. Can you see why they call the 7.000 to 7.300 MHz band 40 meters?
modulation In order to send a message with a radio wave we modify the wave in some predetermined way. A simple scheme is to turn the signal on and off with a code key. With the right receiver we will hear this as the familiar beeping of Morse code.

To send more complex signals, live voice, we need to continuously modulate some property of the wave. These are common choices:
 

unmodulated wave
amplitude modulated
frequency modulated
phase modulated
All of these and variations are in use in the amateur bands. Transmitting and receiving circuits vary with each mode, as do their sensitivity to noise and interference.
schematics Radio circuits are often described with stylized pictures of their components. Here are some examples with their corresponding symbols:
A complete picture is called a schematic. The components of a circuit are often named, and sometimes values are given for their properties.
formula Let's see what we can do with a schematic using just these elements. We can predict what will happen in a circuit by knowing a few principals:
  • Electrical potential E drives a current I through a resistance R. The more current you want, or the more resistance you have, the more potential you'll need to get it. We can say this with the formula:

    • E = I R   or    I = E / R
     
  • Also, the power P delivered from/to an element increases with both potential E and current I at that element. Again, using formulas:

    • P = I E   or   P = I 2 R


Here is a circuit where a 12 volt battery drives a current through a 100 ohm resister. Wonder how much current circulates around this loop?

First we will figure out how much current actually flows in this circuit. Then we will use that result to figure out how much power the battery will deliver to the resistor in the process. 

We can find the current flowing in the loop by plugging these known quantities into our first formula:

E = 12,  R = 100
therefore:
I = E / R = 12 / 100 = .12 amps
Then we can use this result in the formula for power:
P = I E = .12 x 12 = 1.44 watts
The battery delivers 1.44 watts of power to the resistor. This will continue until some circuit parameter changes, such as the battery running down (E < 12 volts), or the resister overheats, or even burns up (R >> 100 ohms). Overheating is a consideration. Normal resistors are only designed to dissipate 1/4 watt.

4.

Safety

This brings us to the issue of safety. We should be careful to not build circuits that catch on fire. It has happened, but it is probably not one of the biggest risks amateur radio operators face. The real risks are:
  • Shocks
  • Falls
high voltage Tube radios often operate with hundreds of volts on exposed circuit elements. Such voltages can easily kill. Do not open these radios without first unplugging the electrical cord and waiting several minutes for circuits to discharge.
rf burns Modern transistor radios are much safer, using 5 to 12 volts in all but the power modules. Still, treat these radios with caution. When transmitting, the antenna circuits can work as a step-up transformer producing hundreds or even thousands of volts. Radio frequency currents tend to stay on the surface of the skin and produce skin burns rather than death.
lightning Antennas are especially dangerous when they fall onto power lines or are struck by lightning. Avoid both by not placing antennas near power lines and by disconnecting antennas from all equipment during storms.
falls Finally, antennas work best when placed high in the air. Often amateur operators build towers and climb them to install antennas. Do not ever climb a tower, or even a tall tree, without appropriate safety equipment and training in its use. A proper climbing harness will allow an operator to clip to the tower while climbing and to safely use both hands while working at the tower top.
Return to Index