The Boring Stuff You Should Know
Background information for the technical questions in the exam

Metric system prefixes and suffixes used in Ham Radio
Giga XXXX = 1,000,000,000 (one thousand million)
Mega XXXX = 1,000,000 (one million times)
Kilo XXXX = 1,000 (one thousand times)
Centi XXXX = 1/100 (one hundredth)
Milli XXXX = 1/1,000 (one thousandth)
Micro XXXX = 1/1,000,000 (one millionth)
Nano XXXX = 1/1,000,000,000 (one thousandth of a Micro)
Pico XXXX = 1/1,000,000,000,000 (one millionth of a millionth)

Example: XXXX is the value you are expressing such as Volts, Amperes, Ohms, Watts, etc. One Kilovolt would be 1,000 Volts, one megaohms would be 1,000,000 ohms , one millivolt would be 0.001 volts

Voltage, Resistance and Current Flow:

Everything we use in our amateur station requires a power source that delivers a specific Voltage and Current capability. Voltage is commonly referred to as Electro Motive Force (EMF) instead of volts. This is like the water pressure at the bottom of a dam. The higher the water in the dam, the more pressure at the bottom of the dam. Current, the flow of electricity, is measured in amperes and is commonly represented by the letter I. This is like the flow of water in a pipe at the bottom of the dam. The amount of water flowing would be limited by the diameter of the pipe and the pressure exerted by the height of the water in the dam. In an electronic circuit the current flow would be limited by the EMF (voltage) and the resistance to current flow measured in ohms.

If we know the voltage and the resistance in a circuit, we can calculate the current that would be flowing using Ohms Law :

Current in amperes (I) is equal to the EMF in volts (E) divided by the resistance in ohms (R).

This Triangle can help you solve for Current, Voltage and Resistance in a circuit. For example: if you have a 12-volt battery connected across a 6-ohm resistor the current flowing would be 2 amperes. You can determine this by covering the value with your thumb to see what you need to do. Cover the I and you will see that it is V (Voltage) divided by R (Resistance) therefore:

Current = 12 volts ÷ 6 Ohms or Current =2 Amperes

Power

Power is work done by electricity and is defined as the voltage across a circuit multiplied by the current flowing through the circuit.

This Triangle can help you solve for Power(in watts) if Voltage and voltage and Current are known. You can determine by covering the P with your thumb to see it is equal to the current (I) times the voltage (V) . Here are a couple of examples:

A circuit connected to 120-volt power outlet that draws 10 amperes would be consuming ? watts.

Power = voltage times the current or Power = 120 x 10 or 1200 watts

A circuit powered by a 12-volt battery that draws 200 milliamperes (ma) would consume 2.4 watts.

Power = voltage times the current or Power = 12 x 0.20 or 2.4 watts

Current Sources:

In the electronic world we have two kinds of commonly encountered sources of electric power:

Direct Current:

Direct Current (DC) is a voltage that has two terminals, one positive and one negative. Typically, DC power is available from batteries, accessory jacks in vehicles, and plug-in power supplies

Some commonly used batteries for amateur radio applications include the following:

· Alkaline and Zinc Carbon cells that produce 1.5 V - available in AAA, AA, C and D cells. These batteries are not rechargeable.

· Lithium batteries that produce 1.5 or 3 volts. A typical example would be AAA, AA and coin cells. These batteries are not rechargeable.

· Nickel Cadmium (NICAD) and Nickel Metal Hydride (NIMH) that produce 1.2 volts, and are available in AAA, AA, C, D cells, and custom shapes. These batteries are rechargeable.

· LiFePo4, Lithium Iron Phosphate Batteries a newer Light weight , longer life rechargeable batteries with flatter discharge voltage characteristic, but the initial cost is higher.

· Flooded Lead Acid batteries that produce 12 volts. Examples are automotive batteries and deep cycle marine batteries. These contain a liquid electrolyte (Sulphuric acid) and must be operated in an upright position. These batteries are rechargeable. These batteries release Hydrogen gas while charging so ventilation is required.

· Sealed Lead Acid batteries – Gel Cells and AGM (Absorbed Glass Mat) batteries that are available in 6-volt and 12-volt versions. They are sealed and use a “gelled” electrolyte and they can be operated in any position. They have high current ratings ranging from smaller ones with a 1 ampere hour rating up to 80 ampere hours and more. These batteries are rechargeable.

Alternating Current

Alternating current is a voltage that alternates between equal positive and negative values. This is what is available from the 120 VAC wall outlet in your home.

The 120 Volts we normally associate with the outlets in our home is the equivalent of a DC value that would provide the same heating effect (or work) as a 120-volt DC voltage. This is known as the RMS value of the AC voltage. The heating effect of AC is less than the peak value because the voltage is continuously changing over the time for each cycle. The peak value of an AC voltage is 1.414 times the RMS value. Therefore the peak voltage for a 120 Volt RMS coming from the outlet in our homes would be 1.414 times 120 volts or 169.68 volts Peak or 339.36 volts peak to peak (measured from the positive peak to the negative peak).

For a pure sine wave the equivalent RMS value is 0.707 times the peak value. Conversely the peak voltage can be calculated as 1.414 times the RMS Value.

Examples:

The peak voltage present in standard 120V RMS AC line voltage is 1.414 x 120V or approx. 170 volts peak. The peak to peak (maximum negative to maximum positive peaks) would be two times the peak voltage or approx. 340 V Peak to Peak.

PP = 2x Peak or PP =2 x (120 x 1.414) or PP = 2 x 169.7 or PP = 339.4 Volts

An AC voltage that reads 65 volts on an RMS meter will have a peak to peak voltage of 184 Volts.

Peak to peak Voltage = 2 x RMS x 1.414 or PP = 2 x 65 x 1.414 or PP = 183.8 V PP

FREQUENCY:
If we start at the first positive peak to the next positive peak of one cycle of our sine wave you will observe that it crosses through Zero twice in the cycle.

The time it takes for one cycle of a sine wave is the period of the sine wave. A 100 Hz sine wave has a period of .01 Seconds (or 10 milliseconds).

Frequency is the number of times that an event happens in one second of time. Shown below is a single cycle of a sine wave, as it would be displayed on an oscilloscope. To determine its frequency, you would divide the time in seconds for one cycle into 1.00.

Examples:
What is the frequency of a sine wave with a 10 ms (millisecond) period for one cycle?
F = 1 ÷ time or F = 1 ÷ 0.010 or F = 100Hz

What is the frequency of a sine wave with a 1 µs (microsecond) period for one cycle?
F = 1 ÷ time or F = 1 ÷ 0.000001 or F = 1,000,000 Hz or 1 MHz

What is the frequency of a sine wave with a 16.666 millisecond period for one cycle?
F = 1 ÷ time or F = 1 ÷ 0.016666 or F = 60.000 Hz

Wavelength:

Wavelength is the physical distance a wave will travel during one cycle usually expressed in meters. Radio waves in free space travel at the speed of light. Light travels at a speed of approximately 300 million meters per second (actual speed of light is 299,792,458 meters every second in free space) in free space. Wavelength is important in amateur radio when designing and building antennas.

We frequently refer to the frequency bands in amateur radio by their wavelength in meters. For instance, 146 Megahertz (MHz) would be the 2-meter band. Wavelength is easily calculated as using the following equation:

Wavelength equals the speed of light (in meters per second) divided by the frequency

Wavelength = 300,000,000 ÷ frequency; or to simplify,

Wavelength = 300 ÷ Frequency (in megahertz)

For the 146 MHz example above this would be:

300,000,000 divided by 146,000,000; or since both values are in millions simply,

300 ÷ 146 or 2.054 meters

This is an important relationship to remember since there are questions in the exam relating to wavelength for a specific frequency or the frequency for a given wavelength.

In amateur radio we frequently refer to our frequencies in terms of approximate wavelength. Since we frequently operating in the Megahertz frequency range, we can simplify our conversion to wavelength by dividing the frequency in megahertz (MHz) into 300. For example:

A 146 MHz signal would be in the 2 meter band --- 300 ÷ 146 = 2.054-meters
A 4.0 MHz signal would be in the 75 meter band --- 300 ÷ 4 = 75-meters

RF Signals and Modulation

Radio frequencies are simply sine waves like we see coming out of the outlet at home except at a much higher Repetition rate (frequency) Radio signals in the AM Broadcast band are operating from 500,000 hertz to 1,700,000 Hertz. This frequency range can be expressed in kilohertz (thousands of hertz as 500 KHz to 1,700 KHz), or in megahertz (millions of hertz) as 0.500 MHz to 1.700 MHz

The frequency of a signal is just the carrier frequency, that is the frequency with no information applied. When we add voice or data to the carrier we are “modulating” or adding information. Simple modulation can be accomplished by varying the frequency of the carrier (Frequency Modulation or FM) or varying the amplitude of the carrier amplitude (Amplitude Modulation or AM).

Amplitude Modulation Frequency Modulation