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

Whip Parabolic

LPAYagi

Rhombic

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