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RF > Mod 5 > Flashcards

Mod 5 Flashcards

1
Q

Transmitter

A

Generates a Radio Frequency (RF) which it will use as the means to transmit intelligence (voice or data that is to be transmitted) by way of an antenna

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2
Q

Receiver

A

reverses the transmit process to recover the intelligence

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3
Q

Electronic Oscillator

A

Generates a constant frequency. This frequency is called a carrier wave.

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4
Q

Audio Amplifier (Transmitter)

A

In a transmitter, takes the weak audio signal and amplifies it to be sent to the modulator

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5
Q

Modulator

A

Superimposes (overlays) the intelligence onto the carrier wave

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6
Q

RF Amplifier

A

Increases signal power to increase the transmit distance

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7
Q

Antenna Tuner/Coupler

A

Enables an antenna to operate over different frequencies by matching impedance of the transmitter and the antenna

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8
Q

Phase Lock Loop

A

Is used to keep the oscillator frequency stable and accurate by means of an error voltage

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9
Q

Carrier Wave

A

Is a pure wave of constant frequency produced by the VCO

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10
Q

Modulation

A

The process of superimposing an input signal onto a carrier wave

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11
Q

RF Control

A

Maintain the transmitter output power (wattage) at a constant level

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12
Q

Filter

A

Passive devices located strategically throughout the transmitter

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13
Q

Audio Amplifier (Receiver)

A

Amplifies intelligence to the proper output level

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14
Q

Mixer

A

Combines the oscillator frequency and received RF frequency to recover the Intermediate Frequency (IF).

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15
Q

DETECTOR (DEMODULATOR)

A

Extracts the intelligence from the IF (carrier).

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16
Q

AUTOMATIC GAIN CONTROL (AGC)

A

Controls the output level (volume control) of the intelligence.

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17
Q

Transceiver

A

Contains both a transmitter and a receiver in one package

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18
Q

Simplex

A

One frequency is used for both transmit and receive. Cannot transmit and receive at the same time

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19
Q

Most military portable and man pack radios are..

A

Simplex

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20
Q

Half-Duplex

A

Uses two frequencies, cannot transmit and receive at the same time

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21
Q

The transmission distance of a _______ radio is extended by using a repeater.

A

Half-Duplex

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22
Q

Full-Duplex

A

Can transmit and receive at the same time

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23
Q

Transceivers are made up of all the same components of transmitters and receivers but the transceiver has an additional component called a _______

A

Transmit/Receive Relay

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24
Q

Switches the oscillator between transmit and receive frequencies in transceivers

A

Transmit/Receive Relay

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25
Q

Allows multi-mode, multi-band, and/or multi-functional wireless devices to be enhanced by using software upgrades

A

Software Defined Radio

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26
Q

What enables the RF carrier to “carry” the intelligence to the distant end

A

Modulation

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27
Q

The three major analog modulation techniques are

A

AM, FM, SSB

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28
Q

Digital modulation techniques include

A

Pulse Code Modulation (PCM), Amplitude Shift Keying (ASK), Binary Phase Shift Keying (BPSK), and Quadrature Amplitude Modulation (QAM).

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29
Q

The modulation process produces three signals at the output of the modulator:

A

The oscillator frequency (carrier), and the Upper Sideband (USB), and the Lower Sideband (LSB)

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30
Q

Simplest way for AM demodulation

A

A single diode rectifier circuit

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31
Q

This technique of AM demodulation reduces the effects of selective fading, provides lower levels of distortion, and improves the signal to-noise ratio

A

Synchronous demodulation

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32
Q

This demodulation technique is normally used only when higher quality is required, and cost is not a major factor.

A

Synchronous demodulation

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33
Q

Advantages of AM

A
  1. Simple to implement.
  2. Can be demodulated using a single diode rectifier circuit.
  3. AM receivers are cheap, as no specialized components are required.
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34
Q

Disadvantages of AM

A
  1. Inefficient use of power. Most of the power consumed by the carrier, which does not carry the intelligence.
  2. Inefficient use of bandwidth. AM requires bandwidth twice the highest audio frequency.
  3. Prone to high levels of noise. Most noise is amplitude based and AM detectors are sensitive to it.
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35
Q

Derived from using two carrier signals that are 90° out of phase

A

Quadrature Amplitude Modulation (QAM)

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36
Q

Single Side Band

A

Consists of only one of the sidebands (either upper or lower). The carrier is suppressed, and the other sideband is eliminated, widely used in the High Frequency (HF)

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37
Q

Peak Envelope Power (PEP)

A

Power measurement for an SSB signal

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38
Q

SSB variants

A

Lower Sideband Single Sideband (LSB SSB)

Upper Sideband Single Sideband (USB SSB)

DSB is Double or Dual Sideband

ISB

AME

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39
Q

Advantages of SSB

A

50% reduction in transmitter power level

Receiver bandwidth can be reduced by half

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40
Q

Disadvantages of SSB

A

More complex circuits that cost more than basic AM

More complex circuits also require more maintenance and expertise.

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41
Q

Different methods to generate frequency modulated signals

A

Varactor Diode Oscillator

Phase Locked Loop (PLL)

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42
Q

Advantages of FM

A

Resilience to noise and interference used for high quality broadcast transmissions.

Easy to apply modulation at low power stage of the transmitter

Use of non-linear RF amplifiers are more efficient than the linear, less battery power is required and makes the use of FM more viable for portable two-way radio applications.

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43
Q

Disadvantages of FM

A

Poor spectrum efficiency

Complicated circuits

Some modes have higher spectrum requirements

Sidebands extend to infinity (filters are required)

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44
Q

Bit

A

a binary digit—a logic one or logic zero

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45
Q

transmission speeds are measured in

A

bits per second (bps)

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46
Q

Byte

A

a unit of digital information that consists of eight bits

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47
Q

The first step in converting an analog signal to a digital signal

A

Sampling

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48
Q

A continuous wave that changes in either amplitude, frequency, or phase to carry data (intelligence)

A

Analog Signal

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49
Q

Digital Signal

A

comprised of bits, which are discrete and finite

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50
Q

Sampling

A

The process of measuring the analog signal to obtain its value, then converting that value to a bit for transmission in a digital circuit

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51
Q

Multiplexer

A

Combines digital voice, video, and data from two or more channels/users into a single composite output signal called an aggregate

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52
Q

In multiplexing, a frame is

A

A collection of data samples taken from the individual user channels

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53
Q

Frame Period

A

is the amount of time it takes for one frame to occur in between Framing Bits

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54
Q

Bandwidth

A

the amount of data transmitted across the network and is expressed as bits per second (bps)

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55
Q

Pulse Code Modulation (PCM)

A

Converts analog voice to digital according to a sampling theorem developed in the 1920’s by Dr. Harry Nyquist. The Nyquist Theorem states that analog voice must be sampled at rate that is twice the highest frequency

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56
Q

PCM involves three steps:

A

Step 1 - Sample
Step 2 - Quantize
Step 3 - Encode

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57
Q

Three basic characteristics of the analog signal

A

frequency, amplitude, and phase

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58
Q

Frequency Shift Keying (FSK)

A

Takes digital information from the user and modulates an analog carrier output by alternating the frequency

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59
Q

Works exactly like FSK except that an alternating voltage (amplitude) will modulate the output carrier

A

Amplitude Shift Keying (ASK)

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60
Q

Binary Phase Shift Keying, Quadrature Phase Shift Keying, and Quadrature Amplitude Modulation—are utilized by ________ only

A

Modems

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61
Q

Modulates the digital data input by shifting the phase of an analog carrier in only two degrees: 0° and 180°

A

Binary Phase Shift Keying (BPSK)

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62
Q

Why is there a Necessity of Digitization

A

Analog signals suffer from many losses such as distortion and interference. Analog signals are also susceptible to security breaches

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63
Q

Transducer

A

Takes a physical input and converts it to an electrical signal.

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64
Q

Source Encoder

A

Compresses the data into a minimum number of bits

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65
Q

Channel Encoder

A

Adds redundant bits to the transmitted data. These are the error correcting bits.

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66
Q

The two types of multiplexing

A

Frequency Division Multiplexing (FDM)

Time Division Multiplexing (TDM)

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67
Q

Frequency Division Multiplexing (FDM)

A

Divides the total frequency bandwidth among its users

Each user is modulated to their individual frequencies, combined, and transmitted on the same link making up the full system bandwidth

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68
Q

Time Division Multiplexing (TDM)

A

Uses time slots to divide the total bandwidth to all connected users

used in most of our military communications

This lets each channel provide input data at its own analog frequency or digital data rate within bandwidth limits

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69
Q

A standard TDM multiplexer normally provides inputs for ___ channels.

A

24

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70
Q

2 modes of TDM multiplexers to transmit data

A

Synchronous, Asynchronous

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71
Q

Mode of TDM that only assigns time slots to channels that are connected on an as-needed basis

A

Asynchronous

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72
Q

Which TDM mode utilizes start and stop bits

A

Asynchronous

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73
Q

Start bits will be a logic _____ and the Stop bit will be a logic ______

A

Zero, One

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74
Q

What makes an asynchronous transmission flow at a synchronous rate

A

Stuffing Bits

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75
Q

How logic ones and zeroes are represented in and out of a multiplexer

A

Signal Format

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76
Q

3 Features of Guided Media

A

Secure
High speed
Shorter distances

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77
Q

3 Advantages of UTP

A

o Least expensive
o Easy installation
o High speed capacity

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78
Q

3 Disadvantages of UTP

A

o Susceptible to external interference
o Lower capacity and performance in comparison to STP
o Short distance transmission due to attenuation

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79
Q

3 Advantages of STP

A

o Better performance at a higher data rate in comparison to UTP
o Crosstalk elimination
o Comparatively faster

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80
Q

3 Disadvantages of STP

A

o Comparatively difficult to install and manufacture
o More expensive
o Bulky

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81
Q

4 Advantages of Coaxial

A
  • High Bandwidth
  • Better noise Immunity
  • Easy to install and expand
  • Inexpensive
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82
Q

The disadvantage of Coaxial

A

Single cable failure can disrupt the entire network

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83
Q

5 Advantages of Optical Fiber

A
  • Increased capacity and bandwidth
  • Light weight
  • Less signal attenuation
  • Immunity to electromagnetic interference
  • Resistance to corrosive materials
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84
Q

4 Disadvantages of Optical Fiber

A
  • Difficult to install and maintain
  • High cost
  • Fragile
  • Unidirectional, i.e., will need another fiber, if we need bidirectional
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85
Q

3 Features of unguided media

A
  • Signal is broadcasted through air
  • Less Secure
  • Used for larger distances
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86
Q

3 major types of Unguided Media

A

Radio Waves, Microwaves, Infrared

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87
Q

Radio waves

A

Easy to generate and penetrate buildings

The sending and receiving antennas need not be aligned

3 KHz to 10 GHz

88
Q

Microwaves

A

Line of sight transmission

Needs antennas to be aligned with each other

Normally 1 GHz to 300 GHz

89
Q

Infrared

A

Short distance

Cannot penetrate through obstacles

300 GHZ to 400 THZ

90
Q

We characterize a radio wave in terms of

A

amplitude, frequency, and wavelength

91
Q

Radio wavelength is the distance between

A

crests of a wave

92
Q

Propagation

A

how radio signals radiate outward from a transmitting source

93
Q

The two basic types of propagation

A

Ground waves and sky waves

94
Q

The ground wave has three components:

A

Direct Wave

Ground Reflected Wave

Surface Wave

95
Q

Direct Wave

A

travels directly through space from transmitting antenna to receiving antenna.

96
Q

Ground Reflected Wave

A

travels through space from the transmitting antenna towards the earth’s surface. It is reflected by the earth’s surface, and travels through space to the receiving antenna.

97
Q

Surface Wave

A

electromagnetic field is induced in the earth’s surface and travels through this medium (dirt, water, etc.) from transmitting antenna to receiving antenna.

98
Q

Medium Frequency (MF)

A

300khz to 3mhz
primarily ground waves, can utilize high frequencies

99
Q

High Frequency (HF)

A

3mhz - 30mhz, ground waves, sky waves, BLOS

100
Q

Ultra High Frequency (UHF)

A

30mhz - 300mhz, ground waves, LOS

101
Q

Very High Frequency (VHF)

A

300mhz - 3ghz. Earth, surface, space, and tropospheric scatter waves

102
Q

Super High Frequency (SHF)

A

3ghz - 30ghz, Earth, surface, space, and tropospheric scatter waves below 5ghz

103
Q

Extremely High Frequency (EHF)

A

30 ghz - 300ghz , Earth, surface and space waves

104
Q

Troposphere

A

Allows for BLOS, high data rate communications using tropospheric scatter radios.

Extends around 11 miles high

105
Q

Ionosphere

A

30 miles above earth

radiation from sun causes particles to lose electrons becoming ionized

106
Q

Ionosphere D Layer

A

Signal absorption occurs here, lowest and densest layer.

AM broadcast is competely absorbed when D layer is present.

106
Q

The incident angle is the angle at which a radio wave enters a layer of the atmosphere

A
106
Q

Ionosphere E Layer

A

Not normally used for long range HF

Anomalies can cause unexpected behavior

107
Q

Ionosphere F layer

A

Divided into F1 and F2

Increasing ionization during the day causes the layer to separate

108
Q

Anomalous Propagation

A

Paths that do not follow a straight line

Refraction, reflection, diffraction

108
Q

Reflection

A

When a wave bounces off a surface or obstruction at the same angle as the angle of incidence

108
Q

F2 Layer

A

most useful for long range sky wave propagation HF

109
Q

Law of reflection

A

the angle of incidences equals the angle of reflection

110
Q

Critical Angle

A

Maximum angle that will reflect off each ionospheric layer

111
Q

Lowest Useable Frequency (LUF)

A

lowest frequency that can be used before it is absorbed in the ionosphere.

112
Q

Optimum frequency for a given layer

A

roughly 85% of MUF

113
Q

Refraction

A

Bending of a wave as it enters a medium of different density

114
Q

A refracted wave will change speed because of..

A

Change in density

115
Q

The amount the wave turns in refraction is determined by …

A

the angle the wave enters, size of the wave and speed of wavelength

116
Q

Diffraction

A

the scientific process involving the bending of a wave as it encounters a constriction or edge

117
Q

Lower frequencies diffract more due to

A

Longer wavelengths

118
Q

Shadow Zone

A

An Area where RF signals, those of higher frequencies, are blocked by an obstruction

119
Q

Ducting

A

When a wave enters a layer of the atmosphere and contuines to reflect within the same layer

120
Q

Scintillation

A

Sudden changes in atmospheric temperatures can cause varying degrees of refraction

121
Q

Rapid changes to signals direction causes

A

Signal to lose amplitude, resulting in weaker signals

122
Q

Tropospheric scintillation

A

Rapid fluctuation of amplitude or phase occurs

123
Q

Free Space

A

Space from the transmitting antenna to the receiving antenna

124
Q

Free space loss

A

the ratio of the receieved power to the transmitted power

125
Q

In satellite com, free space loss is inversely proptional to

A

dish diameter

126
Q

Path loss

A

Reduction in total power density of an electromagnetic wave as it propagates

difference between power transmitted and power received

127
Q

2 Most common and impactful types of path loss

A

Free space loss and atmospheric attenuation

128
Q

Attenuation

A

Loss of energy or power of the RF signal while traveling through the air

129
Q

Attenuation increases as frequency __________

A

Increases

130
Q

Scintillation is caused by

A

Random air pockets with different densities

131
Q

Scintillation is more severe at lower elevation angles due to..

A

Increased travel time in the troposphere

132
Q

Antenna efficiency

A

Compares power delivered to the antenna versus power transmitted

133
Q

Main product of inefficient antenna

A

Reflected energy

134
Q

The most common loss of energy from an antenna is caused by

A

Impedance mismatch

135
Q

Dummy load

A

Test equipment that is an inefficient antenna

136
Q

Impedance Matching

A

Ensures max power transfer
When capacitance and inductance are equal, resistance is 0 (real) (voltage and current are in phase)

When capacitance and inductance are unequal, resistance is imaginary

137
Q

Standing voltage

A

Caused by impedance mismatch between radio and antenna.

Power is being reflected back to the radio

138
Q

Voltage Standing Wave Ratio (VSWR)

A

How much power is being reflected back to the radio

139
Q

Which frequency is impedance mismatch more common in?

A

HF and Lower

140
Q

Resonant antenna

A

Has one natural frequency that will transfer maximum power.

works effiently for a given frequency

141
Q

Resonance

A

The frequency an object naturally wants to vibrate at

142
Q

Non - Resonant Antenna

A

a reactive circuit that must be tuned for for resonance.

Not natural, most be electrically tuned to a frequency

143
Q

As wavelength gets shorter frequency __________

A

Increases

144
Q

Law of Reciprocity

A

receive and transmit properties of an antenna are identical

145
Q

Polarization

A

Electromagnetic waves orientation as it travels

Linear or Non linear

Antennas require like polarity to communicate

146
Q

With dissimilar polarization, a 45 degree mismatch will do what to power

A

Half power will be received

147
Q

With dissimilar polarization, a 90 degree mismatch will do what to power

A

Complete signal loss

148
Q

Linear polarization

A

the electrical and magnetic fields travel in the same plane

149
Q

Non linear polarization

A

The fields rotate as they travel, considered circular or elliptical

150
Q

If the E and H field are the same amplitude and non polar, the fields will rotate circular or elliptical?

A

Circular

151
Q

When transmitting to a linear antenna, it is common to use ________ polarized antennas

A

Circularly

152
Q

Antenna Gain

A

Describes the directivity of an antenna

153
Q

Beam Width

A

Size of the antennas peak lobe where power decreases to 50%

154
Q

Mutual Interference

A

Interference from two or more electrical systems affecting all systems equally

155
Q

Whip antenna

A

omni directional

allows for more interference during receiving

1/4 lambda, vertically polarized, uses ground plane to create a ground reflect

156
Q

marconi

A

Whip antenna

157
Q

Dipole Antenna

A

Consists of a conductive wire or rod that is half the length of the max wavelength the antenna operates end to end

1/2 lambda, horizontally polarized

orientation and height above the ground plane will affect radiation pattern

158
Q

Common config of dipole antenna

A

a signal with only 2 lobes parallel to the ground (bidirectional)

159
Q

The take off angle of a horizontal antenna is determined by

A

the relationship between frequency and height of the antenna off the ground

160
Q

When referring to a wire antenna, height is measured in

A

Wavelengths

161
Q

Horn antenna

A

Simplest type

Directs RF energy in the desired direction and provides impedance matching between transmission line and atmosphere

162
Q

We match impedance for

A

Max transfer of power and minimum reflected energy

163
Q

Most common type of antenna

A

Parabolic

164
Q

Parabolic antenna

A

Consists of a parbolic reflector and a horn antenna, referred to as the feed horn.

165
Q

parabolic are commonly used in

A

LOS links sucha s microwave and satalitte links. Large dishes can operate at VhF and above

166
Q

Size of the parabolic antenna is directly proptional to the

A

Gain of the RF

167
Q

In parabolic antennas, The size of the feed horn is inversely proptional to the

A

Frequency

Larger frequency requires a smaller feed horn

168
Q

CTM-15 is used for which antennas

A

B & w, 197A

168
Q

Vertical Whip

A

Vertically polarized, omnidirectional, used for short range links

MF, HF, VHF, UHF

169
Q

AT-197A/GR

A

(Christmas tree)

UHF

omnidirectional

Vertically polarized

ground to aircraft

170
Q

NVIS (Near Vertical Incident Skywave)

A

Horizontal and vertically polarized

Take off angle direct up between 60 and 90 degrees

Short range 0 - 300 miles

lower end of HF

can communicate over mountains

171
Q

B&W

A

Non grounded, folded dipole

HF

Doesnt require coupler to maintain VSWR under 2:1

Physical Set up determines type of propagation, polarzation, and distance of coms

172
Q

AV-2011 Satcom antenna

A

Foldable, high gain, UHF

Very directional, uses right hand circular polarization

173
Q

LOS

A

Coms extend 15% farther than optical horizon, and 33% farther than true horizon

multi channel, wideband coms

174
Q

Repeaters

A

Must be able to perform frequency translation and amplification

175
Q

4 types of repeaters

A

RF, IF, Baseband, and Audio

176
Q

RF Repeater

A

Simplest

largest amount of noise distortion

177
Q

IF repeater

A

The IF is amplified rather than the RF, lowers noise distortion

178
Q

Baseband Repeater

A

The input RF is amplified, IF is changed to a baseband of individual signals

known as back to back radios because of dropping and reinserting groups of traffic

Noise level compared to IF repeater

179
Q

Audio Repeater

A

Also known as back to back radios

most expensive

VF channels are amplified, multiplexed into baseband, modulated on an IF and converted to SHF

180
Q

Limitations of repeaters

A

Distance to be covered
effective range of equipment
terrain
the need to drop/insert users

181
Q

System limit of repeaters in FDM before noise begins

A

8

182
Q

Frequency Translation

A

Ensures the transmit and receive frequencies are different to minimize interference in repeaters

183
Q

Blurring

A

Paths take different amount of time to reach receiver, making high speed inputs harder to see as they arrive at the receiver

184
Q

To overcome polarity, troposcatter systems employ a system comprised of

A

Polarization
Angle
Space
Frequency

185
Q

Troposcatter requires

A

High power transmitters, sensitive receiver, high gain antennas

Cheaper than using satellites for medium distance

186
Q

2G

A

First cellular data, 1991

introduced encrypting phone calls and texts

187
Q

3G

A

Speeds from 348kbs to 21.6mbs

introduced Network authentication for User equipment (UE) ensures users connected to the network they intended to connect to

188
Q

4G

A

Stopped using circuit switching, uses IP communications

189
Q

5G

A

Uses mid and high band spectrums, covers smaller areas. Cells will be smaller than previous generations

190
Q

CDMA (Code Division Multiple Access)

A

uses a spread spectrum technique to allow a signal with a wider bandwidth spread.

Allows several cell phones to be multiplexed over the same channel

191
Q

GSM (Global System for Mobile Communications)

A

Offers wider international roaming capabilities

192
Q

TDMA (Time Division Multiple Access)

A

Allows several users to share the same frequency channel

Used in GSM

193
Q

popular cellular technologies

A

GSM
GPRS
UMTS
CDMA

194
Q

Base Transceiver Station

A

Enables cellular devices to make direct communication with mobile phones

195
Q

Base Station Controller (BSC)

A

Coordinates with the MSC to interface with the landline based PSTN, VLR, and HLR to route calls toward different base center controllers

196
Q

Cellular network systems channels are categorized into 2 fields:

A

Strong dedicated control channel

Strong Paging Channel

197
Q

Strong dedicated control channel

A

Used to transmit digital info to a cellular mobile phone from the base station and vice versa

198
Q

Strong Paging Channel

A

For tracking the mobile phones by MSC (Mobile Switching Center) when a call is routed to it

199
Q

A typical cell site offers coverage of how many miles?

A

9-21 miles

200
Q

Handover (in cellular networking)

A

Base stations request to the MSC to transfer the control of a user mobile phone call to receive a stronger signal

201
Q

RoIP

A

Radio over IP

Effective, low cost boost that leverages networks you already have in place (internet, VPN)

adds PTT, radio identification, and frequency change

Links two or more radios using an internet based connection

202
Q

Radio functions added to RoIP

A

PTT

Radio Identification

Identification of the call in progress

Radio carrier operated Switch generates busy signal

Emergency, revive and remote monitoring

203
Q

Benefits of RoIP

A

Save time and money

Broaden your reach

Site linking

204
Q

RoIP Broadening reach:

A

Interoperability, connect users across disparate radio frequiencies, legacy systems, dispatch consoles, computers, and smart phones

205
Q

Push to talk

A

Allows smartphone users to communicate with radio users

206
Q

IP Dispatch

A

Using a soft console, users can operate radios remotely

207
Q

For every sample there is a

A

Frame

208
Q

Multipathing

A

Multiple transmission paths, reciever receieves the signal at differernt times

Causes fading of received signal

209
Q

This freq band suffers from manmade interferences like powerlines

A

HF

210
Q

Which layer of the ionosphere has the most signal absorption

A

D Region
(Because it is the lowest and densest layer

RF (5 decks)

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