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Topic 3 Intro to RFTopic 3 Intro to RFEnabling Objectives3.1 DEFINE the terms: Hertz, Cycle, Frequency, Wavelength, Bandwidth, and EIRP and how they apply in the electromagnetic spectrum.3.2 DISCUSS antenna theory, including directivity, polarization, LOS, and antenna types.3.3 DESCRIBE some of the advantages and disadvantages of circuits operating in the HF through EHF bands.3.4 DESCRIBE types of communication links and multiple access methods.3.5 DEFINE modulation terms, including AM, FM, ASK, FSK, and PSK.3.6 LIST atmospheric layers and DEFINE ionization, reflection, refraction, diffraction, doppler, ducting, and atmospheric variations.3.7 DISCUSS wave transmission properties.
Signals Environment
BACKGROUND
Year(s)
-1895-1901 Marconi invents radio (called “wireless”)
-1945 Arthur Clarke describes concept of using a geo-stationary satellite for communications
-1957 USSR Launches Sputnik
-1967 INTELSAT I (24 voice channels)/DSCS I
-1976 GAPFILLER satcom (used by US Navy)
-1990-present UHF Follow-On (UFO), DSCS III SHF, MILSTAR EHF, Satcom and many more…….
Clarke Orbit - 1945
• Concept conceived by science fiction author Arthur C. Clarke
• Envisioned three artificial satellites in a 24-hour (GEO) orbit, giving complete television and microwave coverage to the entire planet
Moon Relay - 1954
• U.S. Navy experiment - world's first operational space communications system, called Communication by Moon Relay (CMR) was used between 1959 and 1963 to link Hawaii and Washington, DC.
Echo 1 Satellite - 1960
• NASA spacecraft - 100-ft. diameter balloon made of aluminized polyester placed in 800-900 nautical mile orbit
• Radio waves could be reflected off of the smooth aluminum surface
SATCOMUPLINK
SATCOMDOWNLINK
Non-SatelliteCommunications
Radio – communication between two or more points, using electromagnetic waves as the transmission medium
ELF VLF LF MF HF VHF UHF SHF EHF IR VL UV Xrays Gamma rays etc.
THE ELECTROMAGNETIC SPECTRUM
Freq HighLow
Frequency x Wavelength = Speed of Light
Wavelength ShortLong
Radio Portion
RADIO WAVES
1 wavelength
1 wavelength
Higher Frequency
Lower Frequency
Frequency x Wavelength = Speed of Light
Wave Classifications
TravelTravel
Dis
turb
ance
Dis
turb
ance
Transverse Wave
TravelTravel
DisturbanceDisturbance
Longitudinal Wave
Basic Sine Wave
Frequency/Period
1 Second1 Second
4 Hz4 Hz
Wavelength - Distance between points of corresponding phase of Wavelength - Distance between points of corresponding phase of two consecutive cycles of a wave. The distance a wave will travel two consecutive cycles of a wave. The distance a wave will travel (propagate) in one complete cycle.(propagate) in one complete cycle.
= v / f = Propagation velocity / Frequency
e.g., 1 Hz
~ 300,000 Km ~ 186,400 Mi
Am
pli
tud
e
Time
0 .25 .50 .75 1.0 1.25 1.50
e.g., 2 Hz
~ 150,000 Km
Am
pli
tud
e
Time
0 .25 .50 .75 1.0 1.25 1.50
Radio Frequency Terms
Velocity (C)
186,000 Miles186,000 Miles300,000,000 Meters300,000,000 Meters
1 Second1 Second
Relationships
11
TTƒCC
λ냃
ƒƒ= Frequency C = Velocity= Frequency C = Velocity
T = Period T = Period λλ = Wavelength = Wavelength
BandwidthBandwidth - - The width, The width, in Hertz, of the satellite in Hertz, of the satellite signal or channelsignal or channel..• NarrowbandNarrowband• WidebandWideband
Po
wer
50 MHz Bandwidth50 MHz Bandwidth
Frequency
10.475GHz
10.500GHz
10.525GHz
Center Freq
• Throughput - The number of bits per second of information passing through a data communication system. Also referred to as data rate.
Maximum Throughput is directly proportional to BW
Radio Frequency Related Terms
Bandwidth
A signal is centered at 15kHz with a A signal is centered at 15kHz with a total BW of 6kHz. How does it look in total BW of 6kHz. How does it look in
the spectrum?the spectrum?
00kHzkHz
55kHzkHz
1010kHzkHz
1515kHzkHz
2020kHzkHz
2525kHzkHz
3030kHzkHz
Antennas
Directivity
• Unidirectional - Receives or radiates efficiently in one direction only.
• Bi-directional - Receives or radiates efficiently in two directions, 180 degrees apart.
• Omnidirectional - Receives or radiates efficiently in all directions 360 degrees.
Unidirectional Antenna
Omnidirectional
Polarization
• Vertical
• Horizontal
• Right Hand Circular
• Left Hand Circular
How the wave propagates
in relation to the Earth.
Line Of Sight
Antenna Types
• There are vast number of antenna types used for many different purposes.
– Whip– Rhombic– Log-Periodic– Parabolic– Arrays
FRD-10/WullenweberCircular Disposed Antenna
Array(CDAA)
SIMPLEX One Direction Only
(e.g., GBS)
POINT APOINT A POINT BPOINT B
HALF DUPLEX Two Directions, One At A TimePOINT APOINT A POINT BPOINT B
POINT APOINT A POINT BPOINT BFULL DUPLEX
Two Directions Simultaneously(like a telephone)
Types of Comm Links
SATCOM Related Terms
• EIRP - Effective Isotropic Radiated Power– Power that a theoretical isotropic (point) radiator
would have to put out in all directions to equal the actual power transmitted in one direction by a directional antenna.
• Multiple Access– Use of the allocated spectrum (channel / transponder)
by multiple users:• FDMA - Frequency Division Multiple Access• TDMA - Time Division Multiple Access• SSMA - Spread Spectrum Multiple Access
FDMA PowerA B C
Frequency
Some of the Bandwidth,all of the time
BW
Time
TDMA Power
A B C
T1 T2 T3
BW BW BW
All of the Bandwidthsome of the time
FRAME
SSMA
Time
Freq
ABC
AB
C
AB
CAB
C
All of the Bandwidthall of the time- DSSS (CDMA)- Frequency hopping
SATCOM Related TermsTypes of Multiple Access
Modulation Terms
• Modulating Wave– Intelligence converted to an electromagnetic
waveform (such as: voice converted from AF to an EM waveform after entering a microphone or telephone)
• Carrier Wave (ƒc)– A Radio Frequency Wave with Constant Amplitude,
Frequency & Phase
• Modulated (complex) Wave– The resultant wave after the modulation process.
AM
• The process of varying the Amplitude
of the Carrier Wave in Accordance with
the Amplitude of the Modulating Wave
DSB
SSB
ISB
FM
ASK
FSK
PSK
UHF
300-3000MHZ
Utility
SHF
3-30GHZCapacity
EHF
30-300GHZSurvivability
UHFAdvantages: Workhorse of Naval Satcom, Very Widespread, Can use small, lightweight equipmentDisadvantages: Low Data Rates, Very crowded, Susceptible to jamming
SHF EHFAdvantages: High Data Rate, Joint interoperabilityDisadvantages: Not widespread, DSCS Crowded, CWSP costSmall antennae make ships “disadvantaged users”
Advantages: LDR:Anti-Jam, Anti-Scint, LPD/LPIMDR: better data rates, less survivability
Disadvantages: LDR slow, Not as widespread as UHFCloud bursts can interfere w/ xmsn
Frequency Band
Low Moderate High
UHF
225 MHz - 3 GHz
High
Moderate Moderate
Low Moderate High
SHF
3 Ghz-30 GHz
Low Moderate
Low Moderate
High
Moderate Moderate
Terminal Cost
Maintenance Cost
Technical Complexity
BW Resources Used
Survivability
EHF
30 GHz - 300 GHz
High
High
Military Utility
Comm-On-The-Move
General Frequency Band Attributes
Att
enu
atio
n (
dB
) 25
20
15
10
5
30
0
10 20 30 40 50
• Light Rain (5mm/hr)• 20º Elevation Angle
C-BandCommercialUp/Dn-Link(~0.8 dB)
Ku-BandCommercialUp/Dn-Link(~3.2 dB)
K-BandGBS & Milstar
Down-Link(~7.0 dB)
Ka-BandCommercialUp/Dn-Link(~13.5 dB)
Ka-BandGBS
Up-Link(~15.5 dB)
Ka-BandMilstarUp-Link(~26 dB)
X-BandDSCS
Up/Dn-Link(~1.5 dB)
Frequency (GHz)
Rain Attenuation vs Frequency
Atmospheric Layers
Radio Phenomena
• IONIZATION
• REFLECTION
• REFRACTION
• DIFFRACTION
• DOPPLER
Ducting
Atmospheric Variations
• Sun Spots– Regular - those which are more or less
regular and occur in cycles. – Irregular - Variations which are unpredictable
and that can drastically affect communications capabilities without any advance warning.
Sun Spot Cycles
Wave Transmission
• Ground Wave– Surface Wave– Space Wave
• Sky Wave
Mutipath Fading