NCATT Radio Communication
Systems Endorsement
Very Low Frequency (VLF) - answer3 KHZ - 30 KHz
Low Frequency (LF) - answer30 KHZ - 300 KHz
Medium Frequency (MF) - answer300 KHZ - 3 MHz
High Frequency (HF) - answer3-30 MHz
Very High Frequency (VHF) - answer30-300 MHz
Ultra High Frequency (UHF) - answer300 MHz - 3 GHz
Super High Frequency (SHF) - answer3-30 GHz
Extremely High Frequency (EHF) - answer30 GHz - 300 GHz
Frequency - answerThe number of electronic field oscillations that take place in one
second (in the case of radio transmissions)
Carrier Wave - answerThe high frequency alternating current that can be modulated to
carry intelligence by propagation as a radio wave
Modulation - answerThe process of changing an electromagnetic wave's ability to
transmit information by varying it's amplitude, phase, or frequency.
AM (amplitude modulation) - answerThe amplitude of the carrier wave varies with the
change in amplitude and frequency of the information signal
FM (frequency modulation) - answerThe carrier amplitude stays constant while the
carrier frequency is changed by the modulating or information signal
Ground Waves - answerBelow HF band (3MHz). They follow the curvature of the earth.
Sky Waves - answerOperate in HF Band (3-30MHz). They travel in straight lines. They
bounce or refract off the ionosphere, which is made up of layers of ionized particles
from about 60-200 miles high. This characteristic can be used to achieve long-range
transmission or radio signals.
, Space Waves - answerWaves transmitted at frequencies above the HF Band. Travel in
straight lines. Do not bounce off ionosphere. Used to communicate with satellites,
signals are above 30 MHz.
Transmitter - answerElectronic unit that accepts information and converts it into a radio
frequency signal capable of being transmitted over long distances
Functions of a Transmitter - answer1.) it must generate a signal of the correct frequency
at a desired point in the EM spectrum
2.) it must provide some form of modulation that causes the information signal to modify
the carrier signal
3.) it must provide sufficient power amplification to ensure that the signal level is high
enough so that it will carry over the desired distance
Oscillator - answerGenerates the carrier signal at the desired frequency
Common Oscillators used in Avionics - answer1.) VFO - Variable Frequency Oscillator
2.) Crystal Oscillator
3.) PLL - Phase Locked Loop Oscillator
Simple Oscillator - answerLC circuit made up of a capacitor and inductor connected in
parallel. The LC circuit has a resonant frequency that matches the desired frequency.
Must have energy fed back into circuit to maintain oscillations
Amplifier - answerComponent that increases the strength of a signal and is found in
both transmitters and receivers. Increases signal strength sent to antenna so that EM
waves will travel a useful distance. Receivers use amplifiers to ensure signal can be
heard.
Basic Types of Amplifiers used in Transmitters - answer1.) Linear
2.) Class C
3.) Switching Amplifiers
Linear Amplifiers - answerClassified as A, AB, or B, provide an output directly
proportional to their input but at a higher power level. All audio amplifiers are linear.
Use of Linear Amplifiers - answerClass A and B amplifiers are used to increase the
power level of changing amplitude radio frequencies such as AM radio signals. FM
signals use more stable non-linear amplifiers such as Class C or switching amplifiers.
Modulator - answerPortion of a transmitter circuit that modulates carrier wave.
Superimposes audio frequency signal onto the carrier wave signal before it is sent to
the antenna.
Demodulator - answerRemoves RF component of the modulated RF signal and
produces an audio frequency output.
Systems Endorsement
Very Low Frequency (VLF) - answer3 KHZ - 30 KHz
Low Frequency (LF) - answer30 KHZ - 300 KHz
Medium Frequency (MF) - answer300 KHZ - 3 MHz
High Frequency (HF) - answer3-30 MHz
Very High Frequency (VHF) - answer30-300 MHz
Ultra High Frequency (UHF) - answer300 MHz - 3 GHz
Super High Frequency (SHF) - answer3-30 GHz
Extremely High Frequency (EHF) - answer30 GHz - 300 GHz
Frequency - answerThe number of electronic field oscillations that take place in one
second (in the case of radio transmissions)
Carrier Wave - answerThe high frequency alternating current that can be modulated to
carry intelligence by propagation as a radio wave
Modulation - answerThe process of changing an electromagnetic wave's ability to
transmit information by varying it's amplitude, phase, or frequency.
AM (amplitude modulation) - answerThe amplitude of the carrier wave varies with the
change in amplitude and frequency of the information signal
FM (frequency modulation) - answerThe carrier amplitude stays constant while the
carrier frequency is changed by the modulating or information signal
Ground Waves - answerBelow HF band (3MHz). They follow the curvature of the earth.
Sky Waves - answerOperate in HF Band (3-30MHz). They travel in straight lines. They
bounce or refract off the ionosphere, which is made up of layers of ionized particles
from about 60-200 miles high. This characteristic can be used to achieve long-range
transmission or radio signals.
, Space Waves - answerWaves transmitted at frequencies above the HF Band. Travel in
straight lines. Do not bounce off ionosphere. Used to communicate with satellites,
signals are above 30 MHz.
Transmitter - answerElectronic unit that accepts information and converts it into a radio
frequency signal capable of being transmitted over long distances
Functions of a Transmitter - answer1.) it must generate a signal of the correct frequency
at a desired point in the EM spectrum
2.) it must provide some form of modulation that causes the information signal to modify
the carrier signal
3.) it must provide sufficient power amplification to ensure that the signal level is high
enough so that it will carry over the desired distance
Oscillator - answerGenerates the carrier signal at the desired frequency
Common Oscillators used in Avionics - answer1.) VFO - Variable Frequency Oscillator
2.) Crystal Oscillator
3.) PLL - Phase Locked Loop Oscillator
Simple Oscillator - answerLC circuit made up of a capacitor and inductor connected in
parallel. The LC circuit has a resonant frequency that matches the desired frequency.
Must have energy fed back into circuit to maintain oscillations
Amplifier - answerComponent that increases the strength of a signal and is found in
both transmitters and receivers. Increases signal strength sent to antenna so that EM
waves will travel a useful distance. Receivers use amplifiers to ensure signal can be
heard.
Basic Types of Amplifiers used in Transmitters - answer1.) Linear
2.) Class C
3.) Switching Amplifiers
Linear Amplifiers - answerClassified as A, AB, or B, provide an output directly
proportional to their input but at a higher power level. All audio amplifiers are linear.
Use of Linear Amplifiers - answerClass A and B amplifiers are used to increase the
power level of changing amplitude radio frequencies such as AM radio signals. FM
signals use more stable non-linear amplifiers such as Class C or switching amplifiers.
Modulator - answerPortion of a transmitter circuit that modulates carrier wave.
Superimposes audio frequency signal onto the carrier wave signal before it is sent to
the antenna.
Demodulator - answerRemoves RF component of the modulated RF signal and
produces an audio frequency output.
