9/11/2012

ReviewRadio Signals &

Electricity

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System of Metric UnitsSystem of Metric Units

1/18/11 HPST Technician Course 2

TeraTera TT 10101212 1,000,000,000,0001,000,000,000,000

GigaGiga GG 101099 1,000,000,0001,000,000,000

MegaMega MM 101066 1,000,0001,000,000

KiloKilo kk 101033 1,0001,000

Basic UnitBasic Unit 101000 11

MilliMilli mm 1010-3-3 0.0010.001

MicroMicro μ 1010-6-6 0.0000010.000001

NanoNano nn 1010-9-9 0.0000000010.000000001

PicoPico pp 1010-12-12 0.0000000000010.000000000001

9/11/20121/18/11 HPST Technician Course 3

109 106 103 102 101 100 10-1 10-2 10-3 10-6 10-9 10-12

G M k h da d c m µ n p giga mega kilo hecto deca deci centi milli micro nano pico

Ampere 1

Milliampere 1/1000

Microampere 1/1,000,000

Nanoampere 1/1,000,000,000

Units of Measurements

Watt 1

Kilowatt 1000

Megawatt 1,000,000

Gigawatt 1,000,000,000

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T5B02 -- What is another way to specify a radio signal frequency of 1,500,000 hertz?

A. 1500 kHzB. 1500 MHzC. 15 GHzD. 150 kHz

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T5B07 -- If a frequency readout calibrated in megahertz shows a reading of 3.525 MHz, what would it show if it were calibrated in kilohertz?

A. 0.003525 kHzB. 35.25 kHzC. 3525 kHzD. 3,525,000 kHz

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T5B01 -- How many milliamperes is 1.5 amperes?

A. 15 milliamperesB. 150 milliamperesC. 1,500 milliamperesD. 15,000 milliamperes

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T5B03 -- How many volts are equal to one kilovolt?

A. One one-thousandth of a voltB. One hundred voltsC. One thousand voltsD. One million volts

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T5B04 -- How many volts are equal to one microvolt?

A. One one-millionth of a voltB. One million voltsC. One thousand kilovoltsD. One one-thousandth of a volt

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T5B05 -- Which of the following is equivalent to 500 milliwatts?

A. 0.02 wattsB. 0.5 wattsC. 5 wattsD. 50 watts

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T5B06 -- If an ammeter calibrated in amperes is used to measure a 3000-milliampere current, what

reading would it show?

A. 0.003 amperesB. 0.3 amperesC. 3 amperesD. 3,000,000 amperes

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T5B08 -- How many microfarads are 1,000,000 picofarads?

A. 0.001 microfaradsB. 1 microfaradC. 1000 microfaradsD. 1,000,000,000 microfarads

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Wavelength

300

fMHz λm

Frequency (MHz) = 300 / Wavelength (meters)Wavelength (meters) = 300 / Frequency (MHz)

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T3B05 -- How does the wavelength of a radio wave relate to its frequency?

A. The wavelength gets longer as the frequency increases

B. The wavelength gets shorter as the frequency increases

C. There is no relationship between wavelength and frequency

D. The wavelength depends on the bandwidth of the signal

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T3B06 -- What is the formula for converting frequency to wavelength in meters?

A. Wavelength in meters equals frequency in hertz multiplied by 300

B. Wavelength in meters equals frequency in hertz divided by 300

C. Wavelength in meters equals frequency in megahertz divided by 300

D. Wavelength in meters equals 300 divided by frequency in megahertz

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T3B07 -- What property of radio waves is often used to identify the different frequency bands?

A. The approximate wavelengthB. The magnetic intensity of wavesC. The time it takes for waves to travel one

mileD. The voltage standing wave ratio of waves

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T3B08 -- What are the frequency limits of the VHF spectrum?

A. 30 to 300 kHzB. 30 to 300 MHzC 300 to 3000 kHzD. 300 to 3000 MHz

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T3B09 -- What are the frequency limits of the UHF spectrum?

A. 30 to 300 kHzB. 30 to 300 MHzC 300 to 3000 kHzD. 300 to 3000 MHz

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T3B11 -- What is the approximate velocity of a radio wave as it travels through free space?

A. 300 kilometers per secondB. 300,000,000 meters per secondC. 300,000 miles per hourD. 186,000 miles per hour

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T5C05 -- What is the unit of frequency?

A. HertzB. HenryC. FaradD. Tesla

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T5C06 -- What is the abbreviation that refers to radio frequency signals of all types?

A. AFB. HFC. RFD. VHF

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Ohm’s Law• E = Electromotive Force

• Force causing electrons to flow.

• I = Current Intensity• Number of electrons

flowing past a point in a given period of time.

• R = Resistance• Opposition to flow of

electrons.

E = I x RI = E/RR = E/I

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T5D01 -- What formula is used to calculate current in a circuit?

A. Current (I) equals voltage (E) multiplied by resistance (R)

B. Current (I) equals voltage (E) divided by resistance (R)

C. Current (I) equals voltage (E) added to resistance (R)

D. Current (I) equals voltage (E) minus resistance (R)

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T5D02 -- What formula is used to calculate voltage in a circuit?

A. Voltage (E) equals current (I) multiplied by resistance (R)

B. Voltage (E) equals current (I) divided by resistance (R)

C. Voltage (E) equals current (I) added to resistance (R)

D. Voltage (E) equals current (I) minus resistance (R)

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T5D03 -- What formula is used to calculate resistance in a circuit?

A. Resistance (R) equals voltage (E) multiplied by current (I)

B. Resistance (R) equals voltage (E) divided by current (I)

C. Resistance (R) equals voltage (E) added to current (I)

D. Resistance (R) equals voltage (E) minus current (I)

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Power Formula

I = P / E

P

E IWatts

Volts Amps

E = P / I

P = E x I

• P = Power• Rate at which energy is

expended.

• E = Voltage• I = Current

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T5A02 -- Electrical power is measured in which of the following units?

A. VoltsB. WattsC. OhmsD. Amperes

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T5A10 -- Which term describes the rate at which electrical energy is used?

A. ResistanceB. CurrentC. PowerD. Voltage

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T5C08 -- What is the formula used to calculate electrical power in a DC circuit?

A. Power (P) equals voltage (E) multiplied by current (I)

B. Power (P) equals voltage (E) divided by current (I)

C. Power (P) equals voltage (E) minus current (I)

D. Power (P) equals voltage (E) plus current (I)

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T5C09 -- How much power is being used in a circuit when the applied voltage is 13.8 volts DC

and the current is 10 amperes?

A. 138 wattsB. 0.7 wattsC. 23.8 wattsD. 3.8 watts

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T5C10 -- How much power is being used in a circuit when the applied voltage is 12 volts DC and

the current is 2.5 amperes?

A. 4.8 wattsB. 30 wattsC. 14.5 wattsD. 0.208 watts

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T5C11 -- How many amperes are flowing in a circuit when the applied voltage is 12 volts DC and

the load is 120 watts?

A. 0.1 amperesB. 10 amperesC. 12 amperesD. 132 amperes

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Capacitance

• Capacitance is the ability to store energy in an electric field.• The unit of measurement of capacitance is

the Farad (F).• 1F is a very large value.• Capacitors are commonly available in values

ranging from 1pF to a few hundred thousand microfarads.

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The Capacitor

• The function of the capacitor is to temporarily store electrical energy in an electric field.• Like a very temporary storage battery.

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Inductance

• Inductance is the ability to store energy in a magnetic field.• The unit of measurement of inductance is

the Henry (H).• Inductors are commonly available in values

ranging from 1µH to a few Henries.

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The Inductor

• The function of the inductor is to temporarily store electrical energy in a magnetic field.• Basically a coil of wire.

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Reactance & Impedance

• In circuits containing only resistors, voltage & current are always “in phase”.• Current flow changes at the same time and

in the same direction as the voltage change.

• Special kind of resistance to the flow of AC called reactance (X).• Reactance also measured in Ohms (Ω).

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Reactance & Impedance

• In circuits containing capacitors or inductors, voltage & current are “out of phase”.• Voltage changes before the current flow

changes in an inductor.• Voltage “leads” Current

• Current flow changes before the voltage changes in a capacitor.

• Current “leads” Voltage• Remember: ELI the ICE man

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Reactance & Impedance

• Opposition to AC current flow in capacitors or inductors is called reactance (X, XC, or XL).

• Reactance is also measured in Ohms (Ω).

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Reactance & Impedance

• Combination of resistance and reactance is called impedance (Z).• Impedance also measured in Ohms (Ω).

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Resonance

• Because current leads voltage in a capacitor & lags voltage in an inductor, a combination exists where the lead time & lag time cancel, resulting in the current & voltage being in phase.

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Resonance

• This condition is called resonance.• Resonant circuit.• Tuned circuit.• Impedance of a resonant circuit is purely

resistive.• Reactance = 0Ω

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Questions?