Mod 5 Flashcards
Transmitter
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
Receiver
reverses the transmit process to recover the intelligence
Electronic Oscillator
Generates a constant frequency. This frequency is called a carrier wave.
Audio Amplifier (Transmitter)
In a transmitter, takes the weak audio signal and amplifies it to be sent to the modulator
Modulator
Superimposes (overlays) the intelligence onto the carrier wave
RF Amplifier
Increases signal power to increase the transmit distance
Antenna Tuner/Coupler
Enables an antenna to operate over different frequencies by matching impedance of the transmitter and the antenna
Phase Lock Loop
Is used to keep the oscillator frequency stable and accurate by means of an error voltage
Carrier Wave
Is a pure wave of constant frequency produced by the VCO
Modulation
The process of superimposing an input signal onto a carrier wave
RF Control
Maintain the transmitter output power (wattage) at a constant level
Filter
Passive devices located strategically throughout the transmitter
Audio Amplifier (Receiver)
Amplifies intelligence to the proper output level
Mixer
Combines the oscillator frequency and received RF frequency to recover the Intermediate Frequency (IF).
DETECTOR (DEMODULATOR)
Extracts the intelligence from the IF (carrier).
AUTOMATIC GAIN CONTROL (AGC)
Controls the output level (volume control) of the intelligence.
Transceiver
Contains both a transmitter and a receiver in one package
Simplex
One frequency is used for both transmit and receive. Cannot transmit and receive at the same time
Most military portable and man pack radios are..
Simplex
Half-Duplex
Uses two frequencies, cannot transmit and receive at the same time
The transmission distance of a _______ radio is extended by using a repeater.
Half-Duplex
Full-Duplex
Can transmit and receive at the same time
Transceivers are made up of all the same components of transmitters and receivers but the transceiver has an additional component called a _______
Transmit/Receive Relay
Switches the oscillator between transmit and receive frequencies in transceivers
Transmit/Receive Relay
Allows multi-mode, multi-band, and/or multi-functional wireless devices to be enhanced by using software upgrades
Software Defined Radio
What enables the RF carrier to “carry” the intelligence to the distant end
Modulation
The three major analog modulation techniques are
AM, FM, SSB
Digital modulation techniques include
Pulse Code Modulation (PCM), Amplitude Shift Keying (ASK), Binary Phase Shift Keying (BPSK), and Quadrature Amplitude Modulation (QAM).
The modulation process produces three signals at the output of the modulator:
The oscillator frequency (carrier), and the Upper Sideband (USB), and the Lower Sideband (LSB)
Simplest way for AM demodulation
A single diode rectifier circuit
This technique of AM demodulation reduces the effects of selective fading, provides lower levels of distortion, and improves the signal to-noise ratio
Synchronous demodulation
This demodulation technique is normally used only when higher quality is required, and cost is not a major factor.
Synchronous demodulation
Advantages of AM
- Simple to implement.
- Can be demodulated using a single diode rectifier circuit.
- AM receivers are cheap, as no specialized components are required.
Disadvantages of AM
- Inefficient use of power. Most of the power consumed by the carrier, which does not carry the intelligence.
- Inefficient use of bandwidth. AM requires bandwidth twice the highest audio frequency.
- Prone to high levels of noise. Most noise is amplitude based and AM detectors are sensitive to it.
Derived from using two carrier signals that are 90° out of phase
Quadrature Amplitude Modulation (QAM)
Single Side Band
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)
Peak Envelope Power (PEP)
Power measurement for an SSB signal
SSB variants
Lower Sideband Single Sideband (LSB SSB)
Upper Sideband Single Sideband (USB SSB)
DSB is Double or Dual Sideband
ISB
AME
Advantages of SSB
50% reduction in transmitter power level
Receiver bandwidth can be reduced by half
Disadvantages of SSB
More complex circuits that cost more than basic AM
More complex circuits also require more maintenance and expertise.
Different methods to generate frequency modulated signals
Varactor Diode Oscillator
Phase Locked Loop (PLL)
Advantages of FM
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.
Disadvantages of FM
Poor spectrum efficiency
Complicated circuits
Some modes have higher spectrum requirements
Sidebands extend to infinity (filters are required)
Bit
a binary digit—a logic one or logic zero
transmission speeds are measured in
bits per second (bps)
Byte
a unit of digital information that consists of eight bits
The first step in converting an analog signal to a digital signal
Sampling
A continuous wave that changes in either amplitude, frequency, or phase to carry data (intelligence)
Analog Signal
Digital Signal
comprised of bits, which are discrete and finite
Sampling
The process of measuring the analog signal to obtain its value, then converting that value to a bit for transmission in a digital circuit
Multiplexer
Combines digital voice, video, and data from two or more channels/users into a single composite output signal called an aggregate
In multiplexing, a frame is
A collection of data samples taken from the individual user channels
Frame Period
is the amount of time it takes for one frame to occur in between Framing Bits
Bandwidth
the amount of data transmitted across the network and is expressed as bits per second (bps)
Pulse Code Modulation (PCM)
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
PCM involves three steps:
Step 1 - Sample
Step 2 - Quantize
Step 3 - Encode
Three basic characteristics of the analog signal
frequency, amplitude, and phase
Frequency Shift Keying (FSK)
Takes digital information from the user and modulates an analog carrier output by alternating the frequency
Works exactly like FSK except that an alternating voltage (amplitude) will modulate the output carrier
Amplitude Shift Keying (ASK)
Binary Phase Shift Keying, Quadrature Phase Shift Keying, and Quadrature Amplitude Modulation—are utilized by ________ only
Modems
Modulates the digital data input by shifting the phase of an analog carrier in only two degrees: 0° and 180°
Binary Phase Shift Keying (BPSK)
Why is there a Necessity of Digitization
Analog signals suffer from many losses such as distortion and interference. Analog signals are also susceptible to security breaches
Transducer
Takes a physical input and converts it to an electrical signal.
Source Encoder
Compresses the data into a minimum number of bits
Channel Encoder
Adds redundant bits to the transmitted data. These are the error correcting bits.
The two types of multiplexing
Frequency Division Multiplexing (FDM)
Time Division Multiplexing (TDM)
Frequency Division Multiplexing (FDM)
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
Time Division Multiplexing (TDM)
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
A standard TDM multiplexer normally provides inputs for ___ channels.
24
2 modes of TDM multiplexers to transmit data
Synchronous, Asynchronous
Mode of TDM that only assigns time slots to channels that are connected on an as-needed basis
Asynchronous
Which TDM mode utilizes start and stop bits
Asynchronous
Start bits will be a logic _____ and the Stop bit will be a logic ______
Zero, One
What makes an asynchronous transmission flow at a synchronous rate
Stuffing Bits
How logic ones and zeroes are represented in and out of a multiplexer
Signal Format
3 Features of Guided Media
Secure
High speed
Shorter distances
3 Advantages of UTP
o Least expensive
o Easy installation
o High speed capacity
3 Disadvantages of UTP
o Susceptible to external interference
o Lower capacity and performance in comparison to STP
o Short distance transmission due to attenuation
3 Advantages of STP
o Better performance at a higher data rate in comparison to UTP
o Crosstalk elimination
o Comparatively faster
3 Disadvantages of STP
o Comparatively difficult to install and manufacture
o More expensive
o Bulky
4 Advantages of Coaxial
- High Bandwidth
- Better noise Immunity
- Easy to install and expand
- Inexpensive
The disadvantage of Coaxial
Single cable failure can disrupt the entire network
5 Advantages of Optical Fiber
- Increased capacity and bandwidth
- Light weight
- Less signal attenuation
- Immunity to electromagnetic interference
- Resistance to corrosive materials
4 Disadvantages of Optical Fiber
- Difficult to install and maintain
- High cost
- Fragile
- Unidirectional, i.e., will need another fiber, if we need bidirectional
3 Features of unguided media
- Signal is broadcasted through air
- Less Secure
- Used for larger distances
3 major types of Unguided Media
Radio Waves, Microwaves, Infrared
Radio waves
Easy to generate and penetrate buildings
The sending and receiving antennas need not be aligned
3 KHz to 10 GHz
Microwaves
Line of sight transmission
Needs antennas to be aligned with each other
Normally 1 GHz to 300 GHz
Infrared
Short distance
Cannot penetrate through obstacles
300 GHZ to 400 THZ
We characterize a radio wave in terms of
amplitude, frequency, and wavelength
Radio wavelength is the distance between
crests of a wave
Propagation
how radio signals radiate outward from a transmitting source
The two basic types of propagation
Ground waves and sky waves
The ground wave has three components:
Direct Wave
Ground Reflected Wave
Surface Wave
Direct Wave
travels directly through space from transmitting antenna to receiving antenna.
Ground Reflected Wave
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.
Surface Wave
electromagnetic field is induced in the earth’s surface and travels through this medium (dirt, water, etc.) from transmitting antenna to receiving antenna.
Medium Frequency (MF)
300khz to 3mhz
primarily ground waves, can utilize high frequencies
High Frequency (HF)
3mhz - 30mhz, ground waves, sky waves, BLOS
Ultra High Frequency (UHF)
30mhz - 300mhz, ground waves, LOS
Very High Frequency (VHF)
300mhz - 3ghz. Earth, surface, space, and tropospheric scatter waves
Super High Frequency (SHF)
3ghz - 30ghz, Earth, surface, space, and tropospheric scatter waves below 5ghz
Extremely High Frequency (EHF)
30 ghz - 300ghz , Earth, surface and space waves
Troposphere
Allows for BLOS, high data rate communications using tropospheric scatter radios.
Extends around 11 miles high
Ionosphere
30 miles above earth
radiation from sun causes particles to lose electrons becoming ionized
Ionosphere D Layer
Signal absorption occurs here, lowest and densest layer.
AM broadcast is competely absorbed when D layer is present.
The incident angle is the angle at which a radio wave enters a layer of the atmosphere
Ionosphere E Layer
Not normally used for long range HF
Anomalies can cause unexpected behavior
Ionosphere F layer
Divided into F1 and F2
Increasing ionization during the day causes the layer to separate
Anomalous Propagation
Paths that do not follow a straight line
Refraction, reflection, diffraction
Reflection
When a wave bounces off a surface or obstruction at the same angle as the angle of incidence
F2 Layer
most useful for long range sky wave propagation HF
Law of reflection
the angle of incidences equals the angle of reflection
Critical Angle
Maximum angle that will reflect off each ionospheric layer
Lowest Useable Frequency (LUF)
lowest frequency that can be used before it is absorbed in the ionosphere.
Optimum frequency for a given layer
roughly 85% of MUF
Refraction
Bending of a wave as it enters a medium of different density
A refracted wave will change speed because of..
Change in density
The amount the wave turns in refraction is determined by …
the angle the wave enters, size of the wave and speed of wavelength
Diffraction
the scientific process involving the bending of a wave as it encounters a constriction or edge
Lower frequencies diffract more due to
Longer wavelengths
Shadow Zone
An Area where RF signals, those of higher frequencies, are blocked by an obstruction
Ducting
When a wave enters a layer of the atmosphere and contuines to reflect within the same layer
Scintillation
Sudden changes in atmospheric temperatures can cause varying degrees of refraction
Rapid changes to signals direction causes
Signal to lose amplitude, resulting in weaker signals
Tropospheric scintillation
Rapid fluctuation of amplitude or phase occurs
Free Space
Space from the transmitting antenna to the receiving antenna
Free space loss
the ratio of the receieved power to the transmitted power
In satellite com, free space loss is inversely proptional to
dish diameter
Path loss
Reduction in total power density of an electromagnetic wave as it propagates
difference between power transmitted and power received
2 Most common and impactful types of path loss
Free space loss and atmospheric attenuation
Attenuation
Loss of energy or power of the RF signal while traveling through the air
Attenuation increases as frequency __________
Increases
Scintillation is caused by
Random air pockets with different densities
Scintillation is more severe at lower elevation angles due to..
Increased travel time in the troposphere
Antenna efficiency
Compares power delivered to the antenna versus power transmitted
Main product of inefficient antenna
Reflected energy
The most common loss of energy from an antenna is caused by
Impedance mismatch
Dummy load
Test equipment that is an inefficient antenna
Impedance Matching
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
Standing voltage
Caused by impedance mismatch between radio and antenna.
Power is being reflected back to the radio
Voltage Standing Wave Ratio (VSWR)
How much power is being reflected back to the radio
Which frequency is impedance mismatch more common in?
HF and Lower
Resonant antenna
Has one natural frequency that will transfer maximum power.
works effiently for a given frequency
Resonance
The frequency an object naturally wants to vibrate at
Non - Resonant Antenna
a reactive circuit that must be tuned for for resonance.
Not natural, most be electrically tuned to a frequency
As wavelength gets shorter frequency __________
Increases
Law of Reciprocity
receive and transmit properties of an antenna are identical
Polarization
Electromagnetic waves orientation as it travels
Linear or Non linear
Antennas require like polarity to communicate
With dissimilar polarization, a 45 degree mismatch will do what to power
Half power will be received
With dissimilar polarization, a 90 degree mismatch will do what to power
Complete signal loss
Linear polarization
the electrical and magnetic fields travel in the same plane
Non linear polarization
The fields rotate as they travel, considered circular or elliptical
If the E and H field are the same amplitude and non polar, the fields will rotate circular or elliptical?
Circular
When transmitting to a linear antenna, it is common to use ________ polarized antennas
Circularly
Antenna Gain
Describes the directivity of an antenna
Beam Width
Size of the antennas peak lobe where power decreases to 50%
Mutual Interference
Interference from two or more electrical systems affecting all systems equally
Whip antenna
omni directional
allows for more interference during receiving
1/4 lambda, vertically polarized, uses ground plane to create a ground reflect
marconi
Whip antenna
Dipole Antenna
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
Common config of dipole antenna
a signal with only 2 lobes parallel to the ground (bidirectional)
The take off angle of a horizontal antenna is determined by
the relationship between frequency and height of the antenna off the ground
When referring to a wire antenna, height is measured in
Wavelengths
Horn antenna
Simplest type
Directs RF energy in the desired direction and provides impedance matching between transmission line and atmosphere
We match impedance for
Max transfer of power and minimum reflected energy
Most common type of antenna
Parabolic
Parabolic antenna
Consists of a parbolic reflector and a horn antenna, referred to as the feed horn.
parabolic are commonly used in
LOS links sucha s microwave and satalitte links. Large dishes can operate at VhF and above
Size of the parabolic antenna is directly proptional to the
Gain of the RF
In parabolic antennas, The size of the feed horn is inversely proptional to the
Frequency
Larger frequency requires a smaller feed horn
CTM-15 is used for which antennas
B & w, 197A
Vertical Whip
Vertically polarized, omnidirectional, used for short range links
MF, HF, VHF, UHF
AT-197A/GR
(Christmas tree)
UHF
omnidirectional
Vertically polarized
ground to aircraft
NVIS (Near Vertical Incident Skywave)
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
B&W
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
AV-2011 Satcom antenna
Foldable, high gain, UHF
Very directional, uses right hand circular polarization
LOS
Coms extend 15% farther than optical horizon, and 33% farther than true horizon
multi channel, wideband coms
Repeaters
Must be able to perform frequency translation and amplification
4 types of repeaters
RF, IF, Baseband, and Audio
RF Repeater
Simplest
largest amount of noise distortion
IF repeater
The IF is amplified rather than the RF, lowers noise distortion
Baseband Repeater
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
Audio Repeater
Also known as back to back radios
most expensive
VF channels are amplified, multiplexed into baseband, modulated on an IF and converted to SHF
Limitations of repeaters
Distance to be covered
effective range of equipment
terrain
the need to drop/insert users
System limit of repeaters in FDM before noise begins
8
Frequency Translation
Ensures the transmit and receive frequencies are different to minimize interference in repeaters
Blurring
Paths take different amount of time to reach receiver, making high speed inputs harder to see as they arrive at the receiver
To overcome polarity, troposcatter systems employ a system comprised of
Polarization
Angle
Space
Frequency
Troposcatter requires
High power transmitters, sensitive receiver, high gain antennas
Cheaper than using satellites for medium distance
2G
First cellular data, 1991
introduced encrypting phone calls and texts
3G
Speeds from 348kbs to 21.6mbs
introduced Network authentication for User equipment (UE) ensures users connected to the network they intended to connect to
4G
Stopped using circuit switching, uses IP communications
5G
Uses mid and high band spectrums, covers smaller areas. Cells will be smaller than previous generations
CDMA (Code Division Multiple Access)
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
GSM (Global System for Mobile Communications)
Offers wider international roaming capabilities
TDMA (Time Division Multiple Access)
Allows several users to share the same frequency channel
Used in GSM
popular cellular technologies
GSM
GPRS
UMTS
CDMA
Base Transceiver Station
Enables cellular devices to make direct communication with mobile phones
Base Station Controller (BSC)
Coordinates with the MSC to interface with the landline based PSTN, VLR, and HLR to route calls toward different base center controllers
Cellular network systems channels are categorized into 2 fields:
Strong dedicated control channel
Strong Paging Channel
Strong dedicated control channel
Used to transmit digital info to a cellular mobile phone from the base station and vice versa
Strong Paging Channel
For tracking the mobile phones by MSC (Mobile Switching Center) when a call is routed to it
A typical cell site offers coverage of how many miles?
9-21 miles
Handover (in cellular networking)
Base stations request to the MSC to transfer the control of a user mobile phone call to receive a stronger signal
RoIP
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
Radio functions added to RoIP
PTT
Radio Identification
Identification of the call in progress
Radio carrier operated Switch generates busy signal
Emergency, revive and remote monitoring
Benefits of RoIP
Save time and money
Broaden your reach
Site linking
RoIP Broadening reach:
Interoperability, connect users across disparate radio frequiencies, legacy systems, dispatch consoles, computers, and smart phones
Push to talk
Allows smartphone users to communicate with radio users
IP Dispatch
Using a soft console, users can operate radios remotely
For every sample there is a
Frame
Multipathing
Multiple transmission paths, reciever receieves the signal at differernt times
Causes fading of received signal
This freq band suffers from manmade interferences like powerlines
HF
Which layer of the ionosphere has the most signal absorption
D Region
(Because it is the lowest and densest layer
