assignments vv modes of propagations of radio waves

8/6/2019 Assignments Vv Modes of Propagations of Radio Waves

1/16

Modes of propagations of radio waves

Radio propagation describes how radio wavesbehave when they are transmitted, or

arepropagated from one point on the Earth to another. Like light waves, radio wavesare affected by the phenomena of reflection, refraction, diffraction, absorption,

polarization and scattering. Consequently, radio waves at different frequencies

propagate in different ways for the velocity of radio wave is related by the product of

the corresponding frequency and wavelength of the wave. Velocity of the wave being

constant, we have different bands of frequencies and accordingly ranges of

wavelength. The tables illustrate the relationship of the modes of propagation of radio

waves of the frequency bands between VLF and EHF.

Fig1

Fig1 describes how the frequency and the wavelength from the electromagnetic

spectrum vary accordingly, as frequency increases, wavelength decreases and

consequently the mode the propagations of the band waves vary.
http://en.wikipedia.org/wiki/Radio_wavehttp://en.wikipedia.org/wiki/Transmittedhttp://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Reflection_(physics)http://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/Scatteringhttp://en.wikipedia.org/wiki/Radio_wavehttp://en.wikipedia.org/wiki/Transmittedhttp://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Reflection_(physics)http://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/Scattering


2/16

Fig2

Fig2 tabulates the band designation for radio waves according to their corresponding

band of frequencies.

Mode of propagation for the corresponding designations

VLF- Guided between the earth and the ionosphere.

LF- Guided between the earth and the D layerof the ionosphere; Surface waves.

MF- Surface waves propagation in E, F layerionospheric refraction at night, when D

layer absorption weakens used for AM broadcasting.

HF- E layerionospheric refraction. F1, F2 layer ionospheric refraction. Used forAM

broadcasting and Single Side Band two-way communications.

VHF- Infrequent E ionospheric refraction. Extremely rare F1,F2 layer ionospheric

refraction during high sunspot activity up to 80 MHz. Used forFM radio broadcasting

and television broadcasting.

UHF- Direct wave. Sometimes tropospheric ducting. Includes American televisionbroadcasting.

SHF- Direct wave.

EHF- Direct wave limited by absorption.
http://en.wikipedia.org/wiki/D_layerhttp://en.wikipedia.org/wiki/Surface_wavehttp://en.wikipedia.org/wiki/F_layerhttp://en.wikipedia.org/wiki/E_layerhttp://en.wikipedia.org/wiki/F2_propagationhttp://www.chemistrydaily.com/chemistry/Amplitude_Modulationhttp://www.chemistrydaily.com/chemistry/Broadcastinghttp://www.chemistrydaily.com/chemistry/Single_Side_Bandhttp://en.wikipedia.org/wiki/Sporadic_E_propagationhttp://en.wikipedia.org/wiki/F2_propagationhttp://www.chemistrydaily.com/chemistry/FM_radiohttp://en.wikipedia.org/wiki/Line-of-sight_propagationhttp://en.wikipedia.org/wiki/Tropospheric_ductinghttp://en.wikipedia.org/wiki/D_layerhttp://en.wikipedia.org/wiki/Surface_wavehttp://en.wikipedia.org/wiki/F_layerhttp://en.wikipedia.org/wiki/E_layerhttp://en.wikipedia.org/wiki/F2_propagationhttp://www.chemistrydaily.com/chemistry/Amplitude_Modulationhttp://www.chemistrydaily.com/chemistry/Broadcastinghttp://www.chemistrydaily.com/chemistry/Single_Side_Bandhttp://en.wikipedia.org/wiki/Sporadic_E_propagationhttp://en.wikipedia.org/wiki/F2_propagationhttp://www.chemistrydaily.com/chemistry/FM_radiohttp://en.wikipedia.org/wiki/Line-of-sight_propagationhttp://en.wikipedia.org/wiki/Tropospheric_ducting


3/16

What is the ionosphere?

The ionosphere is a name for the layer of the earth's atmosphere that is ionized by

solar radiation. The more common name for this radiation is solar wind. The sun's

upper atmosphere (the corona) is very hot and some of its hydrogen and helium are

able escape the sun's gravity. Because the gas is hot and is in a constant stream of

solar energy it becomes a fully ionized plasma. This streaming plasma is the solar

wind, and it flows out past the earth affecting the earth's magnetic field, the

magnetosphere and ionosphere. The Earth receives a lot of energy from the sun in the

form of radiation- about 1370 Watts per square meter.

What is the structure of the ionosphere?

The ionosphere is composed of three main parts: the D, E, and F regions namely;

F-region: 150-1000km contains a range of ion from NO+ and O+ at the bottom to H+and He+ ions at the top. Electron density is highest in this layer.

E-region: 95-150km, contains mostly 02+ ions

D-region: 75-95 kilometers up, relatively weak ionization due to its position at the

bottom.

Our society has learned to use the properties of the ionosphere in many beneficial

ways over the last century (radio, television, satellite communications, etc.) Since the

ionosphere's existence is due to radiation from the sun striking the atmosphere, it

changes in density from daytime to nighttime. All three layers are denser during thedaytime. At night, all layers decrease in density with the D-Layer undergoing the

greatest change. At night the D-Layer virtually disappears.

Fig3

Fig3 illustrates the effect of the sun position and how the ionospheric layers are

affected accordingly, refer to fig4 to have more details about the change inionospheric layers.


4/16

Fig4

In Fig4 we can clearly see the contrast between day and night effects on the

ionosphere. During the day, communication ranging from frequencies of about

3.5MHz and 10MHz is possible but during the night, ad the D layer virtually

disappears, communication can be made from about 10MHz.

During the day, the sky wave coverage reaches a maximum distance of about 2800km

but during the night the maximum sky wave coverage reaches about 3500km

Structure and nature of the Ionosphere with reference to daily, seasonal and

long-term changes

Because the existence of the ionosphere is directly related to radiations emitted from

the sun, the movement of the Earth about the sun or changes in the sun's activity will

result in variations in the ionosphere. These variations are of two general types:

Those which are more or less regular and occur in cycles and, therefore, can

be predicted in advance with reasonable accuracy,

Those which are irregular as a result of abnormal behavior of the sun and,therefore, cannot be predicted in advance.

Both regular and irregular variations have important effects on radio wave

propagation.

Regular Variations

The regular variations that affect the extent of ionization in the ionosphere can be

divided into four main classes: daily, seasonal, 11-year, and 27-day variations.


5/16

Daily Changes

Daily variations in the ionosphere are a result of the 24-hour rotation of the Earth

about its axis. Daily variations of the different layers are summarized as follows;

The D layer reflects VLF (Very Low Frequencies) which is important for long rangeVLF communications; refracts Low Frequencies and Medium Frequencies waves for

short range communications; absorbs High Frequencies waves but has little effect on

Very High Frequencies and above and disappears at night. In the E layer, ionization

depends on the angle of the sun. The E layer refracts HF waves during the day up to

20 megahertz to distances of about 1200 miles. Ionization is greatly reduced at night.

Structure and density of the F region depend on the time of day and the angle of the

sun. This region consists of one layer during the night and splits into two layers

during daylight hours.

Ionization density of the F1 layer depends on the angle of the sun.

Its main effect is to absorb HF waves passing through to the F2 layer.

The F2 layer is the most important layer for long distance HF

communications.

It is a very variable layer and its height and density change with time of day, season,

and sunspot activity. Fig4 illustrate this daily changes in the iononsphere.

Fig4


6/16

Seasonal Changes

Seasonal variations are the result of the Earth revolving around the sun; the relative

position of the sun moves from one hemisphere to the other with changes in seasons.Seasonal variations of the D, E, and F1 layers correspond to the highest angle of the

sun; thus the ionization density of these layers is greatest during the summer. The F2

layer, however, does not follow this pattern; its ionization is greatest in winter and

least in summer, the reverse of what might be expected. As a result, operating

frequencies for F2 layer propagation are higher in the winter than in the summer. In

fig 5 we can clearly see how absorption in dB varies with the seasonal

change( summer and winter) in year 1980.

Fig5


7/16

Long-term changes

As the sun rotates on its own axis sun spots are visible at 27 days interval that is the

approximate period required for the sun to make one complete revolution. The sun

spot cycle have a minimum and a maximum level of sunspot activity that occurs

every eleven years. Radiation originates in the hot regions that overlie sunspot areas.The more sunspots there are, the better the ionisation. The most recent sunspot

maximum occurred in 2002. Fig 6 shows the characteristic changes occurred in the

ionosphere since year 1970-2000

Fig 6


8/16

Satellite Communication

A communication satellite is placed into synchronous orbit. Synchronous orbit of a

satellite means a satellites position remains fixed with respect to the earths rotation

and appear to be stationary when observed form the earth to achieve this synchronousorbit, the satellite stationed approximately 36000km above the Earths surface as

shown in fig 7.

Fig 7

The geostationary satellite is the artificial satellite which looks stationary from the

ground. Three to four geostationary satellites can cover almost the entire surface of

the earth. Most of the artificial satellites actually used for communications or

broadcasting are geostationary satellites.

Altitude: about 36,000km

Orbit: the circle orbit cycle on the equator is the same as the earth's

autorotation time.

Number of Satellites: four (service areas are duplicated.)

Principle Satellite System: Inmarsat Communication System, N-STAR

Communication System, Omunitrucks Communication System

The quasi-zenith satellite is an artificial satellite of the satellite system where one

satellite always stays near the zenith in Japan by positioning at least three satellites

synchronously on the orbit inclined at 45 degrees from the geostationary orbit. As the

ground surface orbit draws the shape of number 8, it's also called "Number 8 OrbitSatellite". It can obtain a high elevation angle to reduce the influence of buildings and

so forth (blocking.)

Altitude: about 36,000km

Orbit: circle orbit crossing with the equator by the angle of 45 degrees

3 as the minimum

The research and development of the satellite communication system is in

progress.


9/16

Fig8 Quasi-zenith satellite

This is roughly divided into three kinds of orbits: highly elliptic orbit, medium earth

orbit, and low earth orbit. The medium and low earth orbits have lower satellite

altitudes to shorten the radio transmission delay, enabling more speedy and smooth

communication. Specifically, the highly elliptic orbit can obtain a higher elevation

angle. It is currently being researched and developed.

Highly Elliptic Orbit (HEO)

1. Altitude: about 40,000km

2. Orbit: about 5-6 hours

3. Number of Satellites: 2-3 as the minimum

4. The system planning is in progress.

Medium Earth Orbit (MEO)

1. Altitude: several thousand - 20,000km (about 10,000km)

2. Orbit: about 5-6 hours3. Number of Satellites: 8-10 (for the entire world)

4. The system planning is in progress.

Low Earth Orbit (LEO)

1. Altitude: 500km - several thousand km (about 1,000km)

2. Orbit: about 5-6 hours

3. Number of Satellites: several dozen (for the entire world)

4. Principle Satellite System: Globalstar Mobile Satellite Communication

System, Orbcomm Mobile Satellite Communication System (IRIDIUMMobile Satellite System)


10/16


11/16

Common terms used

Uplink: transmission of signals to the satellite

Downlink: receiving signals from a satellite

Transponder: electronic system on a satellite that performs reception, frequency

translation, and retransmission of received signals

Microwaves (1GHz to 40GHz) are used for satellite communication because: Microwaves are not affected by the troposphere and move virtually in a

straight line

Unaffected by ionized regions in the upper atmosphere

Microwaves signals start at high frequencies and consequently can carry

proportionately higher information content

Fig 11 Satellite can be used for receiving and transmitting data form different sources from ground

stations to different ground stations


12/16

Advantages and Disadvantages of Satellite Communications

Advantages

High-capacity, long-range

When first deployed, satellite communications had the advantage of being able to

provide high capacity communications over long ranges. This was seen with

applications such as inter-continental transmission of voice, television, and high speed

data. Satellites made this possibly without the requirement of land-based

infrastructure such as submarine coaxial cables. In todays technology environment,

this advantage has lessened with the development of low-cost optical fiber. A single

undersea fiber optic cable system has an approximate capacity of 640 Gbps which

greatly exceeds the combined throughput of the world's 200 commercial

communications satellites (approximately 260 Gbps)

Coverage

A single geostationary satellite can provide communications coverage of 42.4% of the

Earth's surface. This uses much less infrastructure and power than similar coverage

with terrestrial based system would require.

High availability

There are few sources of interference that cannot be factored into the link budget of

the propagation path of the satellite. This results in a very high availability. The major

causes of significant outages are unavoidable natural events, eg sun-transit outages

Good quality

As with high availability, variations in the satellite path are few and well

characterized. The link budget for a particular path can be determined to guarantee a

desired level of quality of service.

Reliability

While the propagation path between Earth stations and satellite can be significant (as

long as 40,000 km for example), all significant propagation parameters are well-

defined, well-understood and can be modeled accurately. Even though long path

lengths lead to large signal attenuation (in excess of 200 dB) path losses are fairly

constant with only a small number of relatively brief disturbances such as sun-transitoutages and magnetic storms. This is still significant better that comparable terrestrial

based systems. For example, satellite communications link budgets need only include

a fade margin of approximately 2 dB in C band, compared with an allowance of more

than 30 dB for terrestrial systems in the same frequency range.


13/16

Disadvantages

Cost

All aspects of satellite systems are expensive by comparison to terrestrial systems. To

survive the environment of space all components need to be of very high grade.Additionally all systems need to have significant redundancy due to the inability to

effect repairs after launch. As well as the satellite segment, the other required

segments are expensive due to size and complexity such as the ground station and the

launch platform

Delay

The time taken for a transmission to travel the large distances required for satellite

communications is significant. For example, a geostationary satellite 36,000 km

above the surface has an uplink/downlink delay of 0.25 s. This results in a half-second

round trip delay. While this may be suitable for some forms of communication such

as voice, for data and/or video communications this will result in an unacceptable

level of performance.Security

Ground stations are generally large and expensive and are easy to locate and destroy.

Satellite communications are also very simple to intercept and very volatile to

jamming of signal or telemetry links.

Reliability

The inability to service the platform once operational and the harsh environment that

the platform will operate in makes satellite communications prone to catastrophic

system failure

System complexity and ownership

Due to the cost and size of a given platform, ownership and associated business issues

can cause problems with operations of the platform.


14/16

REFERENCES:

Principles of Satellite Communications, Michael J Ryan. Argos Press

http://www.thecanadianencyclopedia.comhttp://en.allexperts.com

spaceflightnow.com

sunearthplan.net

http://www.tpub.com/neets/book10/40k.htm

http://www.tpub.com/neets/book10/40h.htm

http://highfrequencyradio.radio-europe.co.uk/

http://www.tpub.com/content/neets/14182/css/14182_74.htm

https://reader009.{domain}/reader009/html5/0518/5afe020954166/5afe020fdf9de.jpg-

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter1/ion2.htmlhttp://www.qsl.net/vu2msy/propagation.htmb



http://en.wikipedia.org/wiki/Radio_propagation

http://www.sgr.org.uk/ArmsControl/schematic-overview-small_NL23.png

https://reader009.{domain}/reader009/html5/0518/5afe020954166/5afe021081dd1.jpg

http://www.sgr.org.uk/ArmsControl/StarWarsSpaceControl_NL23.htm

http://images.google.mu/images?

hl=en&rlz=1C1GGLS_enMU363MU363&um=1&q=Spotless+Sun&sa=N&start=36

&ndsp=18

http://www.nasa.gov/topics/solarsystem/features/spotless_sun.html

http://www.daviddarling.info/encyclopedia/M/MEO.html

http://www.compassroseintl.com/pubs/Intro_to_sats.html

http://www.nss.gc.ca/site/ss/magazine/vol13_2/beacons_e.asp

http://www.aero.org/publications/crosslink/summer2003/02_06b.html

http://www.sgr.org.uk/ArmsControl/StarWarsSpaceControl_NL23.htm

http://www.globalsecurity.org/space/library/report/1998/sbirs-brochure/part08.htm

http://www.tele.soumu.go.jp/e/adm/system/satellit/move/index.htm
http://www.thecanadianencyclopedia.com/http://en.allexperts.com/http://www.tpub.com/neets/book10/40k.htmhttp://www.tpub.com/neets/book10/40h.htmhttp://www.tpub.com/neets/book10/40h.htmhttp://highfrequencyradio.radio-europe.co.uk/http://www.tpub.com/content/neets/14182/css/14182_74.htmhttp://graphics8.nytimes.com/images/2009/07/20/science/21sunspots.4-1200.jpghttp://graphics8.nytimes.com/images/2009/07/20/science/21sunspots.4-1200.jpghttp://apollo.lsc.vsc.edu/classes/met130/notes/chapter1/ion2.htmlhttp://www.qsl.net/vu2msy/propagation.htmbhttp://www.qsl.net/vu2msy/propagation.htmbhttp://www.tpub.com/content/neets/14182/css/14182_75.htmhttp://www.tpub.com/content/neets/14182/css/14182_66.htmhttp://en.wikipedia.org/wiki/Radio_propagationhttp://www.sgr.org.uk/ArmsControl/schematic-overview-small_NL23.pnghttp://www.globalsecurity.org/space/library/report/1998/sbirs-brochure/fig-20-1.jpghttp://www.sgr.org.uk/ArmsControl/StarWarsSpaceControl_NL23.htmhttp://images.google.mu/images?hl=en&rlz=1C1GGLS_enMU363MU363&um=1&q=Spotless+Sun&sa=N&start=36&ndsp=18http://images.google.mu/images?hl=en&rlz=1C1GGLS_enMU363MU363&um=1&q=Spotless+Sun&sa=N&start=36&ndsp=18http://images.google.mu/images?hl=en&rlz=1C1GGLS_enMU363MU363&um=1&q=Spotless+Sun&sa=N&start=36&ndsp=18http://www.nasa.gov/topics/solarsystem/features/spotless_sun.htmlhttp://www.daviddarling.info/encyclopedia/M/MEO.htmlhttp://www.compassroseintl.com/pubs/Intro_to_sats.htmlhttp://www.nss.gc.ca/site/ss/magazine/vol13_2/beacons_e.asphttp://www.aero.org/publications/crosslink/summer2003/02_06b.htmlhttp://www.sgr.org.uk/ArmsControl/StarWarsSpaceControl_NL23.htmhttp://www.globalsecurity.org/space/library/report/1998/sbirs-brochure/part08.htmhttp://www.tele.soumu.go.jp/e/adm/system/satellit/move/index.htmhttp://www.thecanadianencyclopedia.com/http://en.allexperts.com/http://www.tpub.com/neets/book10/40k.htmhttp://www.tpub.com/neets/book10/40h.htmhttp://highfrequencyradio.radio-europe.co.uk/http://www.tpub.com/content/neets/14182/css/14182_74.htmhttp://graphics8.nytimes.com/images/2009/07/20/science/21sunspots.4-1200.jpghttp://apollo.lsc.vsc.edu/classes/met130/notes/chapter1/ion2.htmlhttp://www.qsl.net/vu2msy/propagation.htmbhttp://www.tpub.com/content/neets/14182/css/14182_75.htmhttp://www.tpub.com/content/neets/14182/css/14182_66.htmhttp://en.wikipedia.org/wiki/Radio_propagationhttp://www.sgr.org.uk/ArmsControl/schematic-overview-small_NL23.pnghttp://www.globalsecurity.org/space/library/report/1998/sbirs-brochure/fig-20-1.jpghttp://www.sgr.org.uk/ArmsControl/StarWarsSpaceControl_NL23.htmhttp://images.google.mu/images?hl=en&rlz=1C1GGLS_enMU363MU363&um=1&q=Spotless+Sun&sa=N&start=36&ndsp=18http://images.google.mu/images?hl=en&rlz=1C1GGLS_enMU363MU363&um=1&q=Spotless+Sun&sa=N&start=36&ndsp=18http://images.google.mu/images?hl=en&rlz=1C1GGLS_enMU363MU363&um=1&q=Spotless+Sun&sa=N&start=36&ndsp=18http://www.nasa.gov/topics/solarsystem/features/spotless_sun.htmlhttp://www.daviddarling.info/encyclopedia/M/MEO.htmlhttp://www.compassroseintl.com/pubs/Intro_to_sats.htmlhttp://www.nss.gc.ca/site/ss/magazine/vol13_2/beacons_e.asphttp://www.aero.org/publications/crosslink/summer2003/02_06b.htmlhttp://www.sgr.org.uk/ArmsControl/StarWarsSpaceControl_NL23.htmhttp://www.globalsecurity.org/space/library/report/1998/sbirs-brochure/part08.htmhttp://www.tele.soumu.go.jp/e/adm/system/satellit/move/index.htm


15/16


16/16

assignments vv modes of propagations of radio waves

Documents