Study sets, textbooks, questions
Upgrade to remove ads
Terms in this set (148)
Any point on earth that a satellite can communicate with
Can be packed up and deployed anywhere in the world; can be mounted on trucks and trailers in order to provide high bandwidth communications anywhere
What are the limitations of SATCOM?
most expensive form of communication, dependent of external organizations, not easily concealable, affected by the environment
What is the LOS range?
50 miles or 80 km
the standard method of transmitting data at long distances, however installation and maintenance cost are very high, very fragile
How do satellites communicate?
with transponders and a simplex mode
What are transponders
receives, re-transmits and amplifies signals. Can be multiple on one satellite
What allows for high bandwidth communication between two geographically distant terrestrial terminals and will avoid any line of site link connection?
Point-to-Point Satellite Communication
Provides platform for implementation of video broadcasting services
Transmission cost is independent from both the numbers of receivers and extent of geographical distribution
Mesh Satellite Network
Allows several terminals in the same network to communicate with each other via a single relay link through the satellite,
What allows for a mesh network to have minimal time delay between signal transmission and reception?
The single hop nature of this network
What has made mesh networks more cost efficient?
commonly used to implement a mesh network
Hub and Spoke (Star) satellite network
All signals and transmissions from a individual terminal must be routed through a central location or hub
Best suited for large amount of terminals transmitting small amounts of data that are all organized at the hub
What is a massless stream of photons traveling in a wave like pattern at the speed of light?
What are the types of radiation?
Radio Waves *
Radio Frequency theory
theory of how electromagnetic waves travel through space and time
What frequency range does radio waves and microwaves fall under?
10 KHz - 300 GHz
What are the microwave bands?
1 to 2 GHz
4 to 8 GHz
8 to 12 GHz
12 to 18 GHz
18 to 26.5 GHz
26.5 to 40 GHz
110 to 170 GHz
Radiation Hazard Zone
an area that will contaminate any object or organism inside the area
What is the general rule when it comes to Radiation Hazard (RadHaz)?
Standoff from the primary lobe of any satellite antenna should be at least 20 feet
How is polarization of an EM determined?
By the orientation of the electric field in relation to the Earth's surface.
When does circular polarization occur?
Orientation of the E-Plane rotates in phase with the frequency. The amplitude always stays constant.
magnetic vector executes a circle perpendicular to the path of propagation with a frequency equal to that of the wave.
Left-hand circular polarization
Right-hand circular polarization
True or False: Your terminal's receive (Rx) polarization must ALWAYSmatch the transmit (Tx) polarization of the satellite.
What is the original unit of sound measurement?
What is a metric prefix in one tenth?
one tenth of a bel
When power level is doubled, it has a ____ dB gain. Any power level lowered by the same dB will always _____ that power level.
3 and halve
Any power level raised by 10 dB will multiply that power level by a factor of what?
decibels of electrical power with respect to one milliwatt
This level occurs when the measured intensity equals the reference level
0 dBm does not mean nothing or no power! It means that the power level at the measurement point is equal to the established reference level of 1 mW
Process of superimposing a signal onto a carrier wave for transmission.
What is Amplitude Modulation?
The signal strength of the carrier wave changes. The change represents the varying modulating signal.
What is it when the carrier wave's number of cycles per second is varied to represent the varying modulating signal?
What is another name for phase modulation?
What is phase modulation?
The direction of the carrier wave is modified to represent the varying modulating signal (intelligence).
Certain types of signals have characteristics that allow them to travel more efficiently as they propagate to the distant end
What is keying?
"Toggle" the current ON and OFF from the sending unit to the receiving unit
What is it called when a standard switching sequence of the reference signal ON and OFF is used to denote a specific character?
Amplitude shift keying
Frequency shift keying
When a specific frequency represents an ON state and another frequency an OFF state
Phase shift keying
When a specific phase of a signal represents an ON state and another phase for an OFF state
What is frequency translation?
The process of moving a signal from one part of the frequency axis, to another part of the axis.
When is frequency translation done?
In wireless communications systems to move a pass band signal to base band before demodulation.
What is encoding?
converting from analog to digital or digital to analog
This type of coding combines clocking signal and data signalBit represented by high/low state, as well as synchronizing itself
What is sequential encoding?
When the channel symbol is uniquely determined by the sequence of output letters from the message source up to that time
This type of encoding uses an algorithm to decode information in CDMA and GSM cellular networks.
What is the carrier wave in Bi-phase shift keying (BPSK) shifted at?
0 and 180 degrees
Quadra Phase Shift Keying (QPSK)
Phase of the carrier wave is shifted at 0, 90, 180, and 270 degrees
Offset Quadra-Phase Shift Keying (OQPSK)
Variation of QPSK Phase of the carrier wave is shifted at 90 degree increments from prior state
What uses 1/2 the bandwidth of BPSK
The number of symbol changes (waveform changes orsignaling events) made to the transmission medium per second using a digitally modulated signal
Also referred to as baud rate
Each symbol represents a phase change
What is the symbol rate for BPSK?
1 symbol created for every bit
What is the symbol rate for QPSK?
1 symbol created for every 2 bits
What is the symbol rate for OQPSK?
1 symbol created for every 2 bits
What is the symbol rate for 8PSK?
1 symbol for every 3 bits
What does the Forward Error Correction (FEC) do?
Creates data symbols to ensure higher rate of data recovery
What is a high performance forward error correction code that is used to achieve reliable information transfer over bandwidth constrained communication links in the presence of data corrupting noise
This adds check symbols to data to detect and correct errors
1/2 rate; FEC coding
1 data bit in 2 bits out
What is multiple access?
Describes the ability of communications equipment to handle more than one subscriber with minimal or no degradation in signal quality
What is FDMA?
Frequency Division Multiple Access; Simple, Reliable, Easy
Lacks flexibility, uses more bandwidth, lesser throughput
What is a satellite's capability of allowing a number of users (or links) to transmit their signals using a single frequency with a designated BW by allocating specific time intervals in a predetermined sequence
Time Division Multiple Access (TDMA)
What is DAMA?
Demand Assigned Multiple Access-
A technique which matches user demands to available satellite resources
Satellite channels are grouped (pooled) together and DAMA assigns user variable time slots that match the users information transmission (bandwidth) requirements
What are the advantages of TDMA/DAMA?
All stations transmit on the same frequency
More users - increased satellite capability
Uses less satellite bandwidth
No inter-modulation effect
What are the disadvantages of TDMA/DAMA?
Timing becomes critical
Closer monitoring and coordination of network required
The need for synchronization makes the system morecomplex
What is Center Frequency?
Either the arithmetic or geometric mean of the lower and upper cutoff frequency
What is another name for receive frequency?
What is the function of a mixer?
Electronic component that mixes two or more input signals to produce a single (composite) output signal
What is a device that allows frequencies within a certain range and attenuates (rejects) frequencies outside that range?
Low pass filters block what?
frequencies that are too high
High pass filters block what?
frequencies that are too low
A band-pass filter eliminates what?
harmonics created by the mixer
What is an electronic device that accepts an input and reproduces it at a greater amplitude (increases the power)?
What is the need for frequency conversion?
Modem frequencies are not conducive for effectiveatmospheric propagation
What is the frequency range know as the microwave window or the "cleanest band" available?
What conversion involves frequency mixing (Mixer Theory)
4 outputs: sum and difference of inputs and the two original inputs
What is intermodulation?
When the RF waves (frequencies) interact and cause attenuation
What is the natural result of mixing signals?
What is it called when two separate signals of the same frequency when in phase will gain power?
two separate signals of the same frequency when out phase will lose power
What causes reflected power?
Anytime there is transition from one medium to another a certain amount of power is reflected back towards the source due to impedance mismatch
What does reflected power cause?
signal degradation and a possibility of equipment damage in HPAs
What satellite orbit perfect for communications?
geostationary orbits (GEO)
Low Earth Orbit (LEO) are used for what?
International Space Station and space shuttle orbits
What orbits do GPS' use?
medium earth orbits (MEO)
What are polar orbits used for?
spy satellites and mapping
Polar orbits are also what type of orbit
A transponder can see how far?
1/3 of earths surface
What is a satellite footprint?
the signal coverage area
What is an orbit that has a period equal to the earth's rotational period?
How many orbits will a geosynchronous orbit make in 24 hours?
Geostationary orbits are what?
the satellite to effectively hover over a point on the Earth
What must a geostationary orbit be?
in Geosynchronous orbit over the equator with an inclination of +/- 8 degrees
Har far from earth does a geostationary orbit?
How much can a single geostationary see?
42% of the Earth's surface between 81 South and 81 North
What is the result of gravitational attraction of the sun and the moon is an apparent drift of the satellite, typically in a small figure 8 pattern which over time will become larger?
What is it called when fuel is used to periodically correct any changes over the planned lifetime of the satellite?
What is the primary limitation of geostationary?
spacing the satellites along the Geostationary belt so that the limited frequencies allocated to this purpose do not result in interference between satellites on uplink or downlink
What two major groups are satellites broken into?
bus and payload
What is a bus?
The platform that supports the payload from launch through the end of its life
What is a payload?
The specialized equipment needed for the satellite to perform its designed function.
What does a payload typically act like in a communications satellite?
communications repeater; RF signals are received, converted, amplified and transmitted back to Earth
Payloads typically consist of what?
Antenna, Wide-band Receivers, Input and Output Multiplexers, Attenuation Devices, and Amplifiers
What is a satellite antenna called?
What does a satellite antenna do and why is it important?
direct the RF energy to the satellite which is important because of the great distance to/from the satellite
Receive and transmit signals in all directions
Size is determined by frequency, usually a specific fraction of the wavelength
More expensive, provide some directivity to signal
Size is determined by frequency, usually a specific fraction of the wavelength
Parabolic (Dish) Antennas
Most expensive type
Provide maximum directivity
What do the parabolic reflectors act as?
a magnifying glass, that focuses RF energy, referred to as antenna gain (dBi)
What type of parabolic uses two parabolic surfaces primary large concave dish and a secondary small convex dish
Center Feed; Parabolic Dish Antenna
Least expensive and simplest configuration
Decent for smaller antennas
Larger antennas lead to blockage of signal
Offset Feeds; Parabolic Dish Antenna
Very expensive Low blockage and best performance
Usually used in small earth terminals (STT)
Most military parabolic dish systems are offset feed
Who, what, and when of a site survey
completed in the planning phase of communication architecture, the SATCOM operator is ultimately responsible for the Installation Area, clear line of sight, Electromagnetic Interference (EMI), antenna base foundation, grounding power source - standard 110v 20 amp circuits and, Cable Length Limitations - Cat5 100m
What is an installation area?
location in which the operator establishes the SATCOM terminal
What are latitude lines?
lines that run horizontal across the Earth's surface
measured from -90 degrees (south) to 90 degrees (north)
What are longitude line?
lines that run vertical across the Earth's surface measured from -180 degrees (west) to 180 degrees (east)
What is the time at the prime meridian called?
runs along the lines of longitude on the earth
It is the direction of north you would follow to arrive at the very center of the north pole, used for point a to point b on maps
A compass will not point true north because it only points to the magnetic north pole
difference in direction between the true azimuth and the magnetic azimuth.
Direction indicating the direction to your objective
When will the angle of elevation change?
as you move further and closer to the equator
your elevation will always point towards the equator
point in which the Earth's curvatureprevents any further line of sight, in terms of elevation it will always be 0 degrees
What do you combine to get your look angle?
azimuth and the elevation
Global Positioning System
GPS's are receive only systems that require at least 4 or more satellites within line of sight to develop a three-dimensional position on earth
What type of tracking is it when human intervention keeping the antenna pointed at the satellite?
What is memory tracking?
Automated process of keeping the antenna pointed to the satellite using date and time stamped data
What is the automated process of keeping the antenna pointed to the satellite using readings of downlink power?
Measures the variance in RF from the satellite illuminating the antenna
Most accurate, but very complex and expensive
What is it when commanded to move a pre-determined amount and take another power measurement?
what are the link variables?
Transmit Data Rate (BAUD rate)
Link Margin (Bit Error Rate-BER) Earth StationLatitude/Longitude
Spacecraft LongitudeDownlink Frequency
Effective Isotropic Radiated Power (EIRP)
Intermediate Frequency (IF) Receive Bandwidth
Bit Error Rate (BIT)
If you have sent 1,000,000 bits of data and receive 1error then the error rate is 1 in 1 million bits or 1 x E-6
How high of a BIT can FDMA have?
1 x E-7
What is the Energy per bit/ noise(Eb/No)
measure of signal to noise ratio for digital communications.
Strength of signal being received
Signal must be above noise floor
Eb/No of 9 or 10 is good, 14 or higher can result inequipment damage
the amount of signal loss after traveling through the atmosphere and outer space to the satellite
Atmospheric loss varies by location of the terminal, frequency, and weather
Effective Isotropic Radiated Power (EIRP)
estimated gain (measured in dB) of an antenna taking into account the maximum gain of the transmitters, the line loss of cables and connectors, and the antenna size
What is Non-Interfering Basis (NIB)?
All transmit frequencies should be Host Nation Cleared
equipment and line loss due to use of equipment
Other sets by this creator
Radio and antenna specs, TSOC BLOCK II STUDENT GUI…
Other Quizlet sets
Biochemistry Chapter 5
Microeconomics Test #2 Ch. 9,10 &11