Unit 5 Flashcards
The process of superimposing an input signal, also called the intelligence signal onto a carrier wave is called___
Modulation
Time is not a form of modulation.
(T or F)
True
This type of modulation changes the voltage of the RF carrier for transmitting
Amplitude
What parts of the intelligence waveform affect the amplitude of the modulated waveform in amplitude modulation?
Amplitude
In amplitude modulation, what are the output signals of the modulator? (3)
Carrier, Upper Sideband, Lower Sideband
In amplitude modulation, the intelligence is carried in the (2)
Upper and Lower Sideband
What type of modulation inefficiently uses bandwidth and power during transmission?
Amplitude
What are 3 advantages of amplitude modulation?
- simple to implement
- can be demodulated using a single diode rectifier
- Cost
List 3 disadvantages of amplitude modulation
- prone to high noise levels
- inefficient use of power
- inefficient use of bandwidth
In amplitude modulation, how much power is found in the carrier?
50%
In Amplitude Modulation, how much power is found in the upper sideband?
25%
In amplitude modulation, how much power is found in the lower sideband?
25%
What are the variants of Single sideband?
LSB SSB
USB SSB
DSB
ISB
AME (amplitude modulated equivalent)
Single Sideband is widely used in the ___ portion of the frequency spectrum.
HF
3 advantages of single sideband
1.Reduction in transmitter power requirements
2.More effective solution for two way radio comm.
3.Reduced receiver bandwidth by half
Disadvantages of single sideband
1.More complex circuits
2.cost more than AM
3. Circuits require more maintenance
What modulation is resilient to noise and interference and used for high quality broadcast transmission?
Frequency
In FM, what parts of the intelligence waveform affect the frequency of the modulated waveform?
Frequency
In FM, the amount the signal deviates above and below the center frequency is known as___
deviation
2 methods to generate frequency modulated signals
Varactor Diode Oscillator
Phase Lock Loop
The FM demodulator may also be called
detector or discriminator
3 advantages of FM
1.Resilient to noise and interference
2.Easy to apply modulation at low power stage of the transmitter
3.Use of non-linear RF amplifiers are more efficient than the linear
3 disadvantages of FM
Poor spectrum efficiency
Complicated circuits
Some modes have higher spectrum requirements
Binary digit, logic 1 or 0
Bit
Composed of 8 bits
Byte
Bits that contain the user’s data to be transmitted
Information Bits
Bits inserted by communications devices that are NOT part of the user’s data.
Non-Information bits
First step in converting an analog signal to a digital signal.
Sampling
The process of combining the data of multiple users into a single output.
Multiplexing
A collection of data samples taken from the individual user channel during multiplexing.
Frame
Amount of time it takes for one frame to occur in between framing bits
Frame period
Amount of data transmitted across the network and expressed as bits per second.
Bandwidth
Dr. Harry Nyquist created what is known as the Nyquist Theorem which states that analog voice must be sampled __ the highest frequency.
Twice
____ Code Modulation converts analog voice to digital by sampling at ___ times per second.
Pulse, 8,000
Digitize is NOT a step of Pulse Code Modulation. True or False
True
What PCM step assigns a decimal value to sampled signal?
Quantize
What step step in PCM samples the analog input 8,000 times per second?
Sample
What PCM step converts decimal values to 8-bit binary words?
Encode
How many frequencies are used in FSK?
Two
What bits per symbol does FSK output?
1 or 0
How many voltages are used in ASK?
Two
What bits per symbol does ASK output?
1 or 0
ASK is susceptible to noise interference because it involves changing ___ levels between logic states.
Voltage
What type of shift keying creates a logic one for one voltage and a logic zero for another voltage?
ASK
What type of modulation modulates digital data by shifting the phase of an analog carrier in only 2 degrees: 0 and 180?
BPSK
How many bits per symbol does BPSK output?
1
What two different degrees does BPSK modulate digital date in? *
0 and 180
How many bits of data are transmitted per phase shift keying in QPSK? *
2
What type of phase shift keying transitions at 0, 90, 180, and 270 degrees with only two bits?
QPSK
What is the first modulation technique that transmits 3 bits of data per symbol?
QAM
What is widely used for transmitting higher data rates than ordinary amplitude modulated and phase modulated schemes?
QAM
In QAM, what does the third bit indicate?
Amplitude
Does coding for error correction for reception by adding error correcting bits to received data.
Channel Decoder
Takes a physical input and converts it to an electrical signal. Also consists of an analog to digital converter where a digital signal is needed for further processes.
Input transducer and A to D converter
Converts electrical signal into physical output.
Output Transducer and D to A converter
Digitized by sampling and quantizing. Recreates source output without loss of information *
Source Decoder
Compresses data into minimum number of bits to help in effective utilization of bandwidth. Removes the redundant bits and unnecessary excess bits such as zeroes. *
Source Encoder
Allows analog signal to transmit from the transmitter end to receiver end.
Channel
Signal is demodulated as well as converted again from analog to digital and reconstructed.
Digital demodulator and A to D converter
Does coding for error correction. Adds error correcting bits to transmitted data. *
Channel Encoder
Modulated by a carrier and converted to analog from the digital sequence.
Digital Modulator and D to A converter
What is the multiplexing technique that uses timeslots to divide the total bandwidth for all connected users?
Time Division Multiplexing
What is the multiplexing technique that divides total frequency bandwidth amongst its users?
Frequency Division Multiplexing
The synchronous mode of TDM uses ___ bits to establish synchronization between transmit and receive multiplexers.
Frame
The asynchronous mode of TDM uses ___ bits to establish synchronization between transmit and receive multiplexers.
Start/Stop
What mode of TDM is best used for voice and video apps where steady data stream is more important than accuracy?
Isochronous
In the isochronous mode of TDM, ____ bits make an asynchronous transmission flow at a synchronous rate.
Pulse stuffing
4 types of Return to Zero
RZ neutral
RZ Polar
RZ Bipolar
RZ Bipolar with zero suppression
What is a signal format where logic ones are +5V and logic zero is 0V. They will not return to 0V halfway?
NRZ
What is used to break up a long string of consecutive logic zeroes that could lead to synchronization loss?
BZS
What uses phase transitions to represent logic 0s and 1s?
CDI
Increases signal power to increase the transmit distance.
RF Amplifier
An energy source. It provides power to the transmitter components and for broadcasting
Power Supply
Takes the weak audio signal and amplifies it to be sent to the modulator
Audio Amplifier
Generates a constant frequency; this frequency is called a carrier wave
Electronic Oscillator
Enables an antenna to operate over different frequencies by matching the impedance of the transmitter and the antenna.
Antenna Tuner/Coupler
Superimposes (overlay) the intelligence onto the carrier wave (VCO frequency)
Modulator/Mixer
Creates electromagnetic (RF) wave that gets transmitted
Antenna
Phase is NOT a characteristic of an antenna wave. T or F
True
Antenna waves travel at the speed of light. T or F
T
As frequency increases, the radio wavelength will___
decrease
The distance between the crests of a RF wave is the ____
wavelength
How radio signals radiate from the antenna is___
Outward
2 types of propagation
Ground waves
Sky waves
3 components of a ground wave
Direct wave
Ground Reflected Wave
Surface Wave
Also known as a line-of-sight wave, this wave travels in a straight line and must be “seen” by both the transmitting and receiving antennas
Direct wave
This wave is reflected from the surface of the earth between the transmitter and receiver.
Ground reflected wave
This wave is electrically coupled to the surface of the earth.
Surface wave
All ground waves arrive to their destination at the same time. T or F
False
This wave is reflected/refracted off the ionosphere for beyond line-of-sight (BLOS)
Sky Wave
When and what type of frequencies work better with sky waves?
Day and Higher
300KHz-3MHz
Medium Frequency
3MHz-30MHz
High Frequency
30MHz-300MHz
Ultra High Frequency
300MHz-3GHz
Very High Frequency
3GHz-30GHz
Super High Frequency
30GHz-300GHz
Extremely High Frequency
The bending of a wave as it enters a medium of a different density
Refraction
30-56 miles, it is the lowest and densest layer of the ionosphere. This density allows more molecules to collide, dissipating their energy. Dissipates at night
D Layer
When a wave bounces off a surface or obstruction and the same angle as thr angle of incidence
Reflection
The scientific process involving the bending of a wave as it encounters a constriction or edge.
Diffraction
Theoretical space void of free electrons or ions
Free Space
56-93 miles, it is not normally used for HF communications. Anomalies within the layer can cause unexpected behavior of the signal.
E layer
A reduction in total power density of an electromagnetic wave as it propagates
Path Loss
93-300 plus miles, divided into two sub-regions, F1 and F2. Increasing ionization during the day causes the layer to separate into these two regions and they recombine at night
F Layer
The loss experienced by traveling through space
Free Space Loss
The earths atmosphere is divided into distinct layers separated by____
Height
The lowest layer where all the weather occurs is called the _____
Troposphere
The troposphere extends to around ___ miles. (15km) high
11
The layer important for radio communication after the troposphere is the ____.
Ionosphere
____ is the bending of a wave as it enters a medium of different density.
Refraction
The ionosphere is closer to the sun, causing particles to lose electrons & become ____.
Ionized
Free electrons in the ionosphere form into electron clouds that vary in_____.
Thickness
3 layers of Ionosphere
D, E, F
F layer breaks into 2 layers, what are they?
F1 & F2
The bending of a wave as it encounters a construction or edge is known as____.
Diffraction
Signal absorption mainly of occurs in what layer of the ionosphere?
D layer
The D layer is the lowest & densest layer, causing ____ of AM broadcast radio.
Absorption
The E layer is known for _____ in the layer causing unexpected signal behavior.
Anomalies
The F2 layer is most useful for long-range sky wave propagation due to its height. True or False
True
The law of reflection states that the angle of incidence equals the______.
Angle of reflection
Reflection of sky waves in the ionosphere involves a hybrid of ____ & reflection.
Refraction
The critical angle determines whether a frequency will ____ off a layer or penetrate through.
Reflect
Lower frequencies diffract more than higher frequencies due to their
Longer wavelengths
____ is caused by temperate inversion, layers of warm air above layers of cooler air creating a duct.
Ducting
A wave trapped in this wave continues to reflect between the two layers.
Ducting
Caused by random pockets of air; humidity, temperature variations at different altitudes more severe at lower elevation angles, changes refractive index; rapid fluctuation of amplitude or phase of a wave.
Tropospheric Scintillation
____ is development of multiple transmission paths; receiving signals arrive at different times.
Multipathing
____ ____ is the weakening of signals in the atmosphere; amount fluctuates with frequency, geography, location etc.
Atmospheric Attenuation
Loss incurred traveling in free space between transmitting and receiving antenna.
Free Space Loss
Space between transmitting and receiving antenna.
Free Space
Reduction in total power density of an electromagnetic wave as it propagates.
Path Loss
Difference between power transmitted and power received.
Path Loss
What are the 2 types of path loss?
Free Space Loss
Atmospheric Attenuation
Define antenna efficiency
Compares power delivered to the antenna vs power radiated out the antenna
Antenna losses are dissipated as what?
Heat
The most common loss of radiated energy is due to….
Impedance matching
What is an example of a low efficiency antenna?
Dummy Load
What is VSWR?
Voltage Standing Wave Radio
What frequency ranges are impedance mismatches more prevelant?
HF and lower frequency radios
Antennas designed to work efficiently for a given frequency are _____ antennas
Resonant
Antennas required to be tuned with an antenna tuner or coupler to allow maximum power transfer are ____ antennas.
non-resonant
The difference in the length of a wave as its travels through a new medium as compared to free space is the ____ length.
Electrical
Electrical length is measured in ____.
Wavelength
The actual length of the conductor from end to end including the radio connected from the cable to the antenna is the _______.
Physical length
Physical length is measured in _____.
Meters/Feet
Receive and transmit properties of an antenna are identical is the law of ____.
Reciprocity
Which field determines polarization of an antenna?
E
Antennas with a 45 degree polarization mismatch will have a ___ power loss.
Half
Linear polarization consist of what 2 types of polarization.
Vertical and Horizon
It is possible to transmit in circular polarization and receive linear. T or F
True
What radiation patters are plotted as a function of the square of the magnitude of electric and magnetic fields on a db scale?
Power
What radiation patterns are plotted as a function of electric and magnetic fields on a logarithmic scale?
Field
Directivity of an antenna. Ratio of power radiated in a particular direction vs radiated in all directions is known as….
Antenna gain
A theoretical antenna that radiates well in all directions like a sphere is a what type of antenna?
Theoretical isotropic antenna
The size of the antenna peak lobe where power decreases to 50% is beam ____.
width
Another name for usable beam width is___ ___.
half power beam width
Interference from 2 or more electrical systems affecting all systems equally is____
Mutual interference
