The Link - https://drive.google.com/file/d/0B4VLfbiiR_kbU1JvLWFaOUZENFE/view?usp=sharing
http://www.livemint.com/Home-Page/lD9Q8oKr2cSGWtLrynE0YI/India-should-look-at-efficient-lowcost-airports-IndiGos.html
https://onedrive.live.com/?cid=a0bc7de4467a7edc&id=a0bc7de4467a7edc%21833&ithint=folder,&authkey=!AMcfXYz48t_Zcak
https://onedrive.live.com/?cid=F333375EC88B32B8&id=F333375EC88B32B8%21104&authkey=%21AA_Xf4E3roWC-tI
Chapter 1 – Basic Radio
The word 'radio' means the radiation of electromagnetic waves conveying
information, and detection of such waves. Within this meaning, such applications
as telegraphy, telephony, television and a host of navigation aids are all classified
as radio. This volume is primarily concerned with the air navigation aids
commonly used worldwide.
Hertz not only verified Maxwell's prediction but also established
the speed of the radio waves and other properties. He showed that they can
propagate in a vacuum, and that they are stopped by a metallic screen (the
foundation of our present day radar). He calculated wavelengths for various
frequencies and determined the relationship between the two.
Propagation of radio waves
If a source of alternating voltage is connected to a wire (i.e. an aerial) an
oscillating current will be set up in the wire, the electrons of which move about a
mean position. The electric field present in the wire is accompanied by a magnetic
field and at a suitable frequency (in relation to the length of the aerial) both fields
radiate efficiently outward from the wire in the form of electromagnetic or radio
waves. In the earth environment these disturbances travel approximately at the
speed of light, that is,
186000 statute miles per second or
162000 nautical miles per second or
300000000 metres per second or
300000 kilometres per second.
As the waves are alternating fields, the terminology involved with alternating
currents will be looked into first, extending this to radio terminology. An a.c.
voltage in a wire reverses its direction a number of times every second.
Consequently, if a graph of the current in the wire is plotted against time, it will be
found that it is a sine curve
Cycle. A cycle is one complete series of values, or one complete process.
Hertz. One hertz is one cycle per second. The number of cycles per second is
expressed in hertz. (This term is a relatively recent adoption in honour of the
above-mentioned eminent scientist).
Amplitude. Amplitude of a wave is the maximum displacement, or the
maximum value it attains from its mean position during a cycle. It is both positive
and negative. (That part of the curve in Fig. 1.1. above the mean or time axis is
called positive and that part which is below the line is negative.)
Frequency (f). Frequency of an alternating current or a radio wave is the
number of cycles occurring in one second, expressed in hertz (Hz). For example,
500 Hz means 500 cycles per second. Since the number of cycles per second of
normal radio waves is very high it is usual to refer to them in terms of kilohertz,
megahertz and giga-hertz as follows:
1 cycle per second = 1 Hz
1000 Hz = 1 kHz (kilohertz)
1000 kHz = 1 MHz (megahertz)
1000 MHz = 1 GHz (giga hertz)
Wavelength (l). This is the physical distance travelled by the radio wave
during one complete cycle of transmission. It is defined as the distance between
successive crests or the distance between two consecutive points at which the
moving particles of the medium have the same displacement from the mean value
and are moving in the same direction.
Chapter 2 Radio Wave
Propagation
Simple Transmitter
The basic components of a simple radio transmitter are shown in Fig. 2.1.
Oscillator. The purpose of an oscillator is to provide a radio carrier wave. At
very high frequencies a unit called a magnetron may be used to produce the
oscillations.
RF Amplifier. The signals produced by the oscillator are too weak for
transmission and they must be amplified. This amplification is done at the RF
amplifier, which is coupled, to the oscillator, and the outgoing amplified signals
are fed to the modulator.
Microphone and AF Amplifier. Similarly, a microphone produces weak
audio signals, which are amplified by the AF amplifier unit. The amplified signals
are then fed to the modulator.
Modulator. In this unit the audio signals modulate the carrier waves by
varying the amplitude (amplitude modulation) or the frequency (frequency
modulation); the resultant modulated signals are fed for further amplification to
the power amplifier.
Power Amplifier. Modulated signals arriving at this unit (not shown in Fig.
2.1) are finally amplified (by stages if necessary) to the transmission level.
Aerial. Modulated and amplified signals are fed to the aerial by the power
amplifier and the electromagnetic radiation takes place.
General Properties of Radio Waves
1) In a given medium, radio waves travel at a constant speed.
2) When passing from one medium to another of different refractive index, the
velocity of the waves changes. The waves are also deflected towards the
medium of higher refractive index, that is, they change their direction.
3) Radio waves are reflected by objects commensurate with their wavelengths
Radio Spectrum
The electromagnetic spectrum starts at the lower end of the radio frequencies,
that is 30 Hz, and stretches to over ten million, million giga hertz where the
radiation takes the form of gamma radiation. In this vast spectrum, radio
frequencies occupy only a very small part. Different frequencies are found to have
different characteristics and in order to identify frequencies having similar
characteristics the full range of the radio spectrum is divided into various groups
called frequency bands. The frequency bands shown in Table 2.1 are
internationally recognised.
Table 2.1
Frequency band Abbreviation Frequencies Wavelength
extremely low frequency ELF 30-300 Hz 10000-1000 km
voice frequency VF 300-3000 Hz 1000-100 km
very low frequency VLF 3-30 kHz 100-10 km
low frequency LF 30-300 kHz 10000-1000 m
medium frequency MF 300-3000 kHz 1000-100m
high frequency HF 3-30 MHz 100-10m
very high frequency VHF 30-300 MHz 10-1 m
ultra high frequency UHF 300-3000 MHz 100-10 cm
super high frequency SHF 3000-30000 MHz 10-1 cm
extremely high frequency EHF 30000- 300 000 MHz 1-0.1 cm
Radar L band 1000-2000 MHz
Radar S band. 2000-4000 MHz
Radar C band 4000-8000 MHz
Radar X band 8000-12500 MHz
It will, however, be appreciated that these divisions are not 'watertight'
divisions and the characteristics of a particular band may overlap above and below
the demarcation frequency limit in the table.
The earth and its surround
Before we set out to discuss the type of propagation, the properties and the
ranges available in the above frequency bands, let us take a quick look at the
physical elements present on and around the earth.
First of all, the shape of the earth: it is approximately a sphere. This means
that the horizon curves away with distance from the transmission point, and if the
radio waves travelled only in straight lines (as they would, by their basic property)
the reception ranges would be limited to 'optical' distance only. This distance is
given by the formula D = 1.0 SVH, where D is the range in nautical miles and H is
the height in it. Fortunately, we will soon see that radio waves do curve to a
greater or lesser extent with the surface of the earth and in the atmosphere, which
means that the above formula is seldom used.
The conductivity of the earth's surface itself varies: seawater provides a
medium of high conductivity whereas the conductivity of the land surface depends
on its composition. It is fairly high where the soil is rich loam, and very poor in
the sands of a desert or the polar ice caps. The terrain itself varies from flat plains
to tall mountains, from deserts to dense jungles.
Surrounding the earth, our atmosphere is rich in water vapour right up to the
height of the tropopause. Water vapour is the major cause of the weather and the
weather means precipitation, thunderstorms, lightning and so forth. Electrical
activity may be expected in any of these attributes of the weather. The other
characteristics of the atmosphere, pressure, density, temperature, all vary
continually, both horizontally along the surface and with height.
And finally, well above the earth's surface we have electrically conducting
belts of ionised layers caused by the ultraviolet rays of the sun.
Radio waves travel best in the free space. On and around the surface of the
earth they are influenced to a varying degree by the factors discussed in the
preceding paragraphs. We will now study these influences in detail.
Propagation: Surface Waves
When electromagnetic waves are radiated from an omni directional aerial,
some of the energy will travel along the surface of the earth. These waves, gliding
along the surface are called surface waves or ground waves. As we learnt earlier,
it is the nature of radio waves to travel in a straight line. However, in appropriate
conditions they tend to follow the earth's surface giving us increased ranges. But,
what causes them to curve with the surface?
Primarily there are two factors. One, the phenomenon of diffraction and
scattering causes the radio waves to bend and go over and around any obstacles in
their path (see Fig. 2.2). As the earth's surface is full of large and small obstacles,
the waveform is assisted almost continually to curve round the surface. The extent
of diffraction depends on the radio wave's frequency (see Fig. 2.3). The diffraction
is maximum at the lowest end of the spectrum and it decreases as the frequency is
increased. At centimetric wavelengths (SHF) an upstanding obstacle stops the
wave front, causing a shadow behind it. It is because of this effect that LF
broadcasts give good field strength behind a range of hills but there is no reception
on your car radio when going under a railway bridge.
This bending downward is further assisted (the other factor) by the fact that as
a part of the wave-form comes in contact with the surface it induces currents in it,
thereby losing some of its energy and slowing down. This is called surface
attenuation. This slowing down of the bottom gives the wave forms a forward and
downward tilt encouraging it to follow the earth's curvature (see Fig. 2.4).
Thus, bending due to diffraction and tilting due to attenuation (imperfect
conductivity of the surface) cause the waves to curve with the surface. Waves
continue until they are finally attenuated, that is, become undetectable.
Attenuation, in its turn, depends on three factors:
1) The type of the surface. As mentioned earlier, different surfaces have different
conductivities. For a given transmission power a radio wave will travel a longer
distance over the sea than over dry soil. For example an MF transmitter's range
over the sea is nearly double that over the land.
2) Frequency in use. The higher the frequency, the greater the attenuation (see Fig.
2.5).
3) Polarisation of radio waves. Vertically polarised waves are normally used with
minimum attenuation.
In combating attenuation, we have no control over the surface over which the
propagation is to be made. The primary consideration therefore, is the choice of
frequency. We are now ready to summarise the ground ranges expected from
frequencies in various frequency bands.
VLF. Attenuation is least, maximum bending is due to diffraction. Given
sufficient power, ranges of several thousand miles may be obtained.
LF. Attenuation is less and the signals will bend with the earth's surface;
ranges to a distance of 1500 nm may be expected.
MF. Attenuation is now increasing, signals still bend with the surface and the
ranges are approximately 300 to 500 nm, maximum is 1000 nm over the sea.
HF. Severe attenuation, bending is least. The maximum range obtainable is
around 70 to 100 nm.
VHF and above. The signals do not bend and the radio waves travel in a
straight line, giving line-of-sight ranges.
Disadvantages at low frequencies.
Although low frequencies produce very long ranges there are considerable
drawbacks, which prohibit their inconsiderate employment.
1) Low efficiency aerials. Ideally the length of the transmitter and receiver aerials
should each be equal to the wavelength. An aerial approximately half the size of
the wavelength is also considered to be suitable for satisfactory operation. Any
further reduction in the aerial size would result in a loss of efficiency. The
largest aerials are found in the lowest frequency band -VLF.
2) Static is severe at lower frequencies and additional power must be supplied to
combat its effect. The effect of static decreases as the frequency is increased:
VHF is considered to be practically free from static.
3) Installation and power. The cost of initial installation is high and subsequent
power requirement to maintain the desired range giving satisfactory reception is
very large.
It should be noted that the range of a surface wave varies as the square root of
its power which may be written in the form of the equation:
Range (nm) = 3 ×√Power (watts)
Sky Waves
We have seen how surface waves may be transmitted to varying distances in
VLF to HF bands. In these bands, signals may also be received having first been
reflected from a huge reflecting layer surrounding the earth known as the
ionosphere. These reflected signals are referred to as sky waves and they form the
principal mechanism for long range communication.
The Ionosphere
The ionosphere is an electrically conducting sphere, completely surrounding
the earth. The ultra-violet rays from the sun impinging upon the upper atmosphere
cause electrons to be emitted from gas molecules. These free electrons are
believed to form a reflecting layer (positive ions would be too heavy to influence
electromagnetic waves). Because the absorption of the solar radiation is uneven at
different levels in the upper atmosphere, several distinct and separate layers, rather
than one continuous zone, are formed. They are given code names D, E and F (see
Fig. 2.6). During the period 1901-1930, the E layer was more commonly known as
the Kennelly-Heaviside layer, named after its discoverers. The presence of the F
layer was established simultaneously by E. V. Appleton in England and A. F.
Barnett in the USA and direct measurements were made in 1925, when the name F
layer was coined. At present, these belts may be identified either by the code letter
or the layer names. Average heights of these layers are as follows, and there are
diurnal and seasonal variations.
D layer: 50-100 km, average 75 km
E layer:100-150 km, average 125 km
F layer:150-350km, average 225km.
http://www.livemint.com/Home-Page/lD9Q8oKr2cSGWtLrynE0YI/India-should-look-at-efficient-lowcost-airports-IndiGos.html
https://onedrive.live.com/?cid=a0bc7de4467a7edc&id=a0bc7de4467a7edc%21833&ithint=folder,&authkey=!AMcfXYz48t_Zcak
https://onedrive.live.com/?cid=F333375EC88B32B8&id=F333375EC88B32B8%21104&authkey=%21AA_Xf4E3roWC-tI
Chapter 1 – Basic Radio
The word 'radio' means the radiation of electromagnetic waves conveying
information, and detection of such waves. Within this meaning, such applications
as telegraphy, telephony, television and a host of navigation aids are all classified
as radio. This volume is primarily concerned with the air navigation aids
commonly used worldwide.
Hertz not only verified Maxwell's prediction but also established
the speed of the radio waves and other properties. He showed that they can
propagate in a vacuum, and that they are stopped by a metallic screen (the
foundation of our present day radar). He calculated wavelengths for various
frequencies and determined the relationship between the two.
Propagation of radio waves
If a source of alternating voltage is connected to a wire (i.e. an aerial) an
oscillating current will be set up in the wire, the electrons of which move about a
mean position. The electric field present in the wire is accompanied by a magnetic
field and at a suitable frequency (in relation to the length of the aerial) both fields
radiate efficiently outward from the wire in the form of electromagnetic or radio
waves. In the earth environment these disturbances travel approximately at the
speed of light, that is,
186000 statute miles per second or
162000 nautical miles per second or
300000000 metres per second or
300000 kilometres per second.
As the waves are alternating fields, the terminology involved with alternating
currents will be looked into first, extending this to radio terminology. An a.c.
voltage in a wire reverses its direction a number of times every second.
Consequently, if a graph of the current in the wire is plotted against time, it will be
found that it is a sine curve
Cycle. A cycle is one complete series of values, or one complete process.
Hertz. One hertz is one cycle per second. The number of cycles per second is
expressed in hertz. (This term is a relatively recent adoption in honour of the
above-mentioned eminent scientist).
Amplitude. Amplitude of a wave is the maximum displacement, or the
maximum value it attains from its mean position during a cycle. It is both positive
and negative. (That part of the curve in Fig. 1.1. above the mean or time axis is
called positive and that part which is below the line is negative.)
Frequency (f). Frequency of an alternating current or a radio wave is the
number of cycles occurring in one second, expressed in hertz (Hz). For example,
500 Hz means 500 cycles per second. Since the number of cycles per second of
normal radio waves is very high it is usual to refer to them in terms of kilohertz,
megahertz and giga-hertz as follows:
1 cycle per second = 1 Hz
1000 Hz = 1 kHz (kilohertz)
1000 kHz = 1 MHz (megahertz)
1000 MHz = 1 GHz (giga hertz)
Wavelength (l). This is the physical distance travelled by the radio wave
during one complete cycle of transmission. It is defined as the distance between
successive crests or the distance between two consecutive points at which the
moving particles of the medium have the same displacement from the mean value
and are moving in the same direction.
Chapter 2 Radio Wave
Propagation
Simple Transmitter
The basic components of a simple radio transmitter are shown in Fig. 2.1.
Oscillator. The purpose of an oscillator is to provide a radio carrier wave. At
very high frequencies a unit called a magnetron may be used to produce the
oscillations.
RF Amplifier. The signals produced by the oscillator are too weak for
transmission and they must be amplified. This amplification is done at the RF
amplifier, which is coupled, to the oscillator, and the outgoing amplified signals
are fed to the modulator.
Microphone and AF Amplifier. Similarly, a microphone produces weak
audio signals, which are amplified by the AF amplifier unit. The amplified signals
are then fed to the modulator.
Modulator. In this unit the audio signals modulate the carrier waves by
varying the amplitude (amplitude modulation) or the frequency (frequency
modulation); the resultant modulated signals are fed for further amplification to
the power amplifier.
Power Amplifier. Modulated signals arriving at this unit (not shown in Fig.
2.1) are finally amplified (by stages if necessary) to the transmission level.
Aerial. Modulated and amplified signals are fed to the aerial by the power
amplifier and the electromagnetic radiation takes place.
General Properties of Radio Waves
1) In a given medium, radio waves travel at a constant speed.
2) When passing from one medium to another of different refractive index, the
velocity of the waves changes. The waves are also deflected towards the
medium of higher refractive index, that is, they change their direction.
3) Radio waves are reflected by objects commensurate with their wavelengths
Radio Spectrum
The electromagnetic spectrum starts at the lower end of the radio frequencies,
that is 30 Hz, and stretches to over ten million, million giga hertz where the
radiation takes the form of gamma radiation. In this vast spectrum, radio
frequencies occupy only a very small part. Different frequencies are found to have
different characteristics and in order to identify frequencies having similar
characteristics the full range of the radio spectrum is divided into various groups
called frequency bands. The frequency bands shown in Table 2.1 are
internationally recognised.
Table 2.1
Frequency band Abbreviation Frequencies Wavelength
extremely low frequency ELF 30-300 Hz 10000-1000 km
voice frequency VF 300-3000 Hz 1000-100 km
very low frequency VLF 3-30 kHz 100-10 km
low frequency LF 30-300 kHz 10000-1000 m
medium frequency MF 300-3000 kHz 1000-100m
high frequency HF 3-30 MHz 100-10m
very high frequency VHF 30-300 MHz 10-1 m
ultra high frequency UHF 300-3000 MHz 100-10 cm
super high frequency SHF 3000-30000 MHz 10-1 cm
extremely high frequency EHF 30000- 300 000 MHz 1-0.1 cm
Radar L band 1000-2000 MHz
Radar S band. 2000-4000 MHz
Radar C band 4000-8000 MHz
Radar X band 8000-12500 MHz
It will, however, be appreciated that these divisions are not 'watertight'
divisions and the characteristics of a particular band may overlap above and below
the demarcation frequency limit in the table.
The earth and its surround
Before we set out to discuss the type of propagation, the properties and the
ranges available in the above frequency bands, let us take a quick look at the
physical elements present on and around the earth.
First of all, the shape of the earth: it is approximately a sphere. This means
that the horizon curves away with distance from the transmission point, and if the
radio waves travelled only in straight lines (as they would, by their basic property)
the reception ranges would be limited to 'optical' distance only. This distance is
given by the formula D = 1.0 SVH, where D is the range in nautical miles and H is
the height in it. Fortunately, we will soon see that radio waves do curve to a
greater or lesser extent with the surface of the earth and in the atmosphere, which
means that the above formula is seldom used.
The conductivity of the earth's surface itself varies: seawater provides a
medium of high conductivity whereas the conductivity of the land surface depends
on its composition. It is fairly high where the soil is rich loam, and very poor in
the sands of a desert or the polar ice caps. The terrain itself varies from flat plains
to tall mountains, from deserts to dense jungles.
Surrounding the earth, our atmosphere is rich in water vapour right up to the
height of the tropopause. Water vapour is the major cause of the weather and the
weather means precipitation, thunderstorms, lightning and so forth. Electrical
activity may be expected in any of these attributes of the weather. The other
characteristics of the atmosphere, pressure, density, temperature, all vary
continually, both horizontally along the surface and with height.
And finally, well above the earth's surface we have electrically conducting
belts of ionised layers caused by the ultraviolet rays of the sun.
Radio waves travel best in the free space. On and around the surface of the
earth they are influenced to a varying degree by the factors discussed in the
preceding paragraphs. We will now study these influences in detail.
Propagation: Surface Waves
When electromagnetic waves are radiated from an omni directional aerial,
some of the energy will travel along the surface of the earth. These waves, gliding
along the surface are called surface waves or ground waves. As we learnt earlier,
it is the nature of radio waves to travel in a straight line. However, in appropriate
conditions they tend to follow the earth's surface giving us increased ranges. But,
what causes them to curve with the surface?
Primarily there are two factors. One, the phenomenon of diffraction and
scattering causes the radio waves to bend and go over and around any obstacles in
their path (see Fig. 2.2). As the earth's surface is full of large and small obstacles,
the waveform is assisted almost continually to curve round the surface. The extent
of diffraction depends on the radio wave's frequency (see Fig. 2.3). The diffraction
is maximum at the lowest end of the spectrum and it decreases as the frequency is
increased. At centimetric wavelengths (SHF) an upstanding obstacle stops the
wave front, causing a shadow behind it. It is because of this effect that LF
broadcasts give good field strength behind a range of hills but there is no reception
on your car radio when going under a railway bridge.
This bending downward is further assisted (the other factor) by the fact that as
a part of the wave-form comes in contact with the surface it induces currents in it,
thereby losing some of its energy and slowing down. This is called surface
attenuation. This slowing down of the bottom gives the wave forms a forward and
downward tilt encouraging it to follow the earth's curvature (see Fig. 2.4).
Thus, bending due to diffraction and tilting due to attenuation (imperfect
conductivity of the surface) cause the waves to curve with the surface. Waves
continue until they are finally attenuated, that is, become undetectable.
Attenuation, in its turn, depends on three factors:
1) The type of the surface. As mentioned earlier, different surfaces have different
conductivities. For a given transmission power a radio wave will travel a longer
distance over the sea than over dry soil. For example an MF transmitter's range
over the sea is nearly double that over the land.
2) Frequency in use. The higher the frequency, the greater the attenuation (see Fig.
2.5).
3) Polarisation of radio waves. Vertically polarised waves are normally used with
minimum attenuation.
In combating attenuation, we have no control over the surface over which the
propagation is to be made. The primary consideration therefore, is the choice of
frequency. We are now ready to summarise the ground ranges expected from
frequencies in various frequency bands.
VLF. Attenuation is least, maximum bending is due to diffraction. Given
sufficient power, ranges of several thousand miles may be obtained.
LF. Attenuation is less and the signals will bend with the earth's surface;
ranges to a distance of 1500 nm may be expected.
MF. Attenuation is now increasing, signals still bend with the surface and the
ranges are approximately 300 to 500 nm, maximum is 1000 nm over the sea.
HF. Severe attenuation, bending is least. The maximum range obtainable is
around 70 to 100 nm.
VHF and above. The signals do not bend and the radio waves travel in a
straight line, giving line-of-sight ranges.
Disadvantages at low frequencies.
Although low frequencies produce very long ranges there are considerable
drawbacks, which prohibit their inconsiderate employment.
1) Low efficiency aerials. Ideally the length of the transmitter and receiver aerials
should each be equal to the wavelength. An aerial approximately half the size of
the wavelength is also considered to be suitable for satisfactory operation. Any
further reduction in the aerial size would result in a loss of efficiency. The
largest aerials are found in the lowest frequency band -VLF.
2) Static is severe at lower frequencies and additional power must be supplied to
combat its effect. The effect of static decreases as the frequency is increased:
VHF is considered to be practically free from static.
3) Installation and power. The cost of initial installation is high and subsequent
power requirement to maintain the desired range giving satisfactory reception is
very large.
It should be noted that the range of a surface wave varies as the square root of
its power which may be written in the form of the equation:
Range (nm) = 3 ×√Power (watts)
Sky Waves
We have seen how surface waves may be transmitted to varying distances in
VLF to HF bands. In these bands, signals may also be received having first been
reflected from a huge reflecting layer surrounding the earth known as the
ionosphere. These reflected signals are referred to as sky waves and they form the
principal mechanism for long range communication.
The Ionosphere
The ionosphere is an electrically conducting sphere, completely surrounding
the earth. The ultra-violet rays from the sun impinging upon the upper atmosphere
cause electrons to be emitted from gas molecules. These free electrons are
believed to form a reflecting layer (positive ions would be too heavy to influence
electromagnetic waves). Because the absorption of the solar radiation is uneven at
different levels in the upper atmosphere, several distinct and separate layers, rather
than one continuous zone, are formed. They are given code names D, E and F (see
Fig. 2.6). During the period 1901-1930, the E layer was more commonly known as
the Kennelly-Heaviside layer, named after its discoverers. The presence of the F
layer was established simultaneously by E. V. Appleton in England and A. F.
Barnett in the USA and direct measurements were made in 1925, when the name F
layer was coined. At present, these belts may be identified either by the code letter
or the layer names. Average heights of these layers are as follows, and there are
diurnal and seasonal variations.
D layer: 50-100 km, average 75 km
E layer:100-150 km, average 125 km
F layer:150-350km, average 225km.
