Introduction to Radio
Course Code: RP1302 Duration: 1 day Technical Level: 1
Contents
Section 1
A Need for Radio
Section 2
Frequency and Bandwidth
Section 3
Modulation
Section 4
Radio Spectrum
Section 5
Antennas and Transmission Lines
Section 6
Propagation
Section 7
Radio Coverage
Section 8
Radio Interference
Section 9
Analogue and Digital Systems
Glossary
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Introduction to Radio
SECTION 1
A NEED FOR RADIO
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A Need for Radio
CONTENTS
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1
Fibre Optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5
Limitations of Human Voice Projection . . . . . . . . . . . . 1.2
The Radio Carrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6
Electromagnetic Propagation . . . . . . . . . . . . . . . . . . . 1.3
The Radio System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7
Transmission Media . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4
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A Need for Radio
Introduction
This course introduces non-technical staff to the concepts of radio spectrum, the basics of radio communications and
provides an appreciation of the relevant aspects of radio technology and the need for legislative bodies.
Telecommunication is defined as the communication of audio, video and data information over a distance. This
distance could be anything from a few metres to thousands of kilometres.
All electronic communications systems have the basic form illustrated above. The fundamental elements are a
transmitter, a communications channel or medium, and a receiver.
In most systems a human being generates a message, known as ‘information’ or ‘intelligence’. The message is applied
to the transmitter, which then transmits it over the communications channel. The receiver picks up the message and
relays it to another human being at the other end of the link.
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Limitations of Human Voice Projection
The distance over which a human being can project their voice is limited. We do not have sufficient physical power to
achieve distances measured in kilometres.
Supposing these distances could be achieved, further limitations would soon be realised.
The velocity (speed) of sound waves through air is 332 metres/second. It would take such a sound wave approximately
30 seconds to travel 10 km. This would have serious implications for holding any sort of practical conversation.
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A Need for Radio
Electromagnetic Propagation
Forms of electromagnetic energy such as light, electricity and radio waves travel (propagate) at approximately
300,000,000 metres/second, a significant increase on the velocity of sound waves in air. These forms of energy can
cover great distances very quickly. It is this electromagnetic energy that is used as a vehicle to carry information over
potentially vast distances.
The thunderstorm shown in the diagram illustrates the difference in velocity of sound and electromagnetic energy
through air.
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Introduction to Radio
Transmission Media
As electromagnetic energy is used to carry information over distance, a choice needs to be made as to which form of
electromagnetic energy (light, radio or electricity) to use.
Factors affecting this choice include mobility requirements, bandwidth requirements and cost implications.
Metal cable carries electrical currents and has been the traditional method used to connect residential and business
premises into the PSTN (Public Switched Telephone Network).
The main disadvantages of metal cable are restricted capacity over significant distances and cost of installation
compared with other media types.
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A Need for Radio
Fibre Optics
Developments in glass technology and the production of high-quality optical fibre have created a revolution in the field
of digital communications.
Optical fibre provides a low-loss guiding mechanism, which allows light energy to pass from an optical source to an
optical detector. At the optical source, the signal is superimposed on the light and is emitted using either a LED (Light
Emitting Diode) or a laser.
Optical communication has several advantages over metal cable systems, including low transmission loss and high
capacity.
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Introduction to Radio
The Radio Carrier
Radio waves pass through space at approximately the speed of light, 300,000,000 m/sec. This form of electromagnetic
energy can also be used to carry information over a distance. The information to be transmitted has to be
superimposed on a carrier using a technique called modulation. To ‘modulate’ something means to change or vary it.
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A Need for Radio
The Radio System
A basic radio system combines the information to be communicated with a radio carrier in a process known as
modulation. The output (a modulated signal) is transmitted and received across the radio link by antennas. The
received signal is demodulated, that is the original information is extracted from the radio carrier, and is passed to an
output device such as a loudspeaker or visual screen.
This workshop provides an insight into each of these radio system components and highlights the difference between
analogue and digital systems. The relevant section number is show in the diagram.
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Introduction to Radio
SECTION 2
FREQUENCY AND BANDWIDTH
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Frequency and Bandwidth
CONTENTS
Sine Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1
Human Speech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4
Sine Waves 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2
Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5
Time and Frequency Domains . . . . . . . . . . . . . . . . . . 2.3
Commercial Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . 2.6
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Frequency and Bandwidth
Sine Waves
The information to be carried over a telecoms network can be referred to as the ‘baseband information’. This consists
of a finite number of individual sine waves.
A sine wave has four quantities associated with it: velocity, frequency, wavelength and amplitude.
Velocity (v) is the speed at which the waveform travels as it passes through a particular medium such as air or water or
along a piece of wire.
The frequency (ƒ) is the number of waves or cycles that pass a fixed point in one second. Frequency is therefore
measured in cycles per second and is given the unit Hertz (Hz).
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Introduction to Radio
Sine Waves 2
The wavelength l is the distance between two similar points. This could be measured between consecutive crests but
is commonly shown covering one cycle of the wave. Wavelength is measured in metres.
The amplitude often expresses the maximum value of a sine wave. When applied to an audio signal, it is often referred
to as the ‘volume’ or ‘loudness’.
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Frequency and Bandwidth
Time and Frequency Domains
An important factor in understanding any telecommunications system is the relationship between the time-domain and
frequency-domain representation of signals.
Figure a) illustrates a 1 kHz sine wave in the time domain.
Figure b) illustrates the same sine wave in the frequency domain.
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Human Speech
The previous example was of a single audio tone (sine wave) of 1 kHz. Human speech consists of a range of
frequencies from approximately 100 Hz to 5 kHz. When represented in the time domain it appears as a constantly
varying signal. Such a signal is referred to as a complex signal, not because it is difficult to understand, but because it
contains a range of frequencies. The diagram gives an example of such a signal.
As speech consists of a number of frequencies constantly varying in amplitude and frequency, then the representation
in the frequency domain at any instant in time may also look something like the example shown above.
The time domain axis shows the sum of all the frequency components present.
Every waveform that is not a pure sine wave is known as a ‘complex wave’. This consists of a number of frequency
components (sine waves).
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Frequency and Bandwidth
Bandwidth
Bandwidth may be defined as the range between the lowest and highest frequencies of a signal.
To hear (receive) a single tone, all that needs to be received is that same single tone.
To hear (receive) a speech signal exactly as it was transmitted, all the frequency components need to be received. All
of these frequencies are constituent parts of the information.
Because the speech signal comprises more information, it occupies a wider bandwidth than the single tone.
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Commercial Bandwidth
The human ear can detect frequencies in the range of approximately 20 Hz to 15,000 Hz. However, to save costs in
communication systems, a narrower bandwidth is used. Measurements show that if certain frequency components are
removed from the speech signal its intelligibility is still retained.
Most voice energy is transferred in the low frequencies between 600–700 Hz. Some energy is transferred in
frequencies beyond 10,000 Hz, but this adds very little to the intelligibility of the signal to the human ear as shown
above by the solid line. The dashed line shows the portion of the frequency band that carries emotion. Therefore, for
economical transfer of intelligible speech, a much narrower bandwidth than 20 to 15,000 Hz (15 kHz) is possible.
In many communication systems speech occupies the range of frequencies from 300–3400 Hz, giving a bandwidth of
3.1 kHz as specified in the ITU-T (International Telecommunication Union – Telecommunication Standardisation Sector)
Recommendations G.132 and G.151. This is often referred to as the nominal 4 kHz voice channel. It is considered a
good compromise between quality and cost.
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Introduction to Radio
SECTION 3
MODULATION
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Modulation
CONTENTS
Radio Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1
DSB (Double Sideband) Modulation . . . . . . . . . . . . . . 3.6
Radio Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2
FM (Frequency Modulation) . . . . . . . . . . . . . . . . . . . . 3.7
Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3
Radio Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8
AM (Amplitude Modulation) . . . . . . . . . . . . . . . . . . . . . 3.4
Spectral Mask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9
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Modulation
Radio Transmitters
Transmitters are the devices which generate the required transmit frequency – the radio carrier.
The carrier is then modulated by the baseband information signal prior to being amplified by the power amplifier.
Frequency Generator
The frequency generator produces a pure sinusoidal waveform at the exact carrier frequency for which the system has
been licensed. A programmable frequency synthesiser is the preferred device used in modern equipment. The power
output of this device is very low.
Modulator
The modulator combines the radio carrier with the baseband information signal to create the modulated signal to be
transmitted. Filtering is applied after the modulator to ensure the modulated spectrum fits into the licensed bandwidth.
The power output of this device is very low.
RF (Radio Frequency) Power Amplifier
The radio signal is amplified to the licensed output power and filtered again, before being applied to the antenna
system.
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Introduction to Radio
Radio Receivers
Receivers are the devices which pick up the transmitted signal, amplify it and then extract the baseband information
signal.
RF Amplifier
The radio frequency amplifier takes the received signal and amplifies it prior to processing. The received signal
strength can be extremely small compared with that at the transmitter – hence the need for amplification.
Demodulator
The demodulator separates the baseband information from the RF carrier.
Baseband Power Amplifier
This device amplifies the baseband signal to a sufficient level to drive the required output device, i.e. a loudspeaker or
television screen.
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Modulation
Modulation
The process of modulation superimposes an information signal such as voice or music onto a higher frequency,
referred to as an RF carrier. At the receiver, demodulation or detection is used to remove the information from the
received modulated carrier.
There are two families of modulating techniques: analogue and digital. Modulation techniques generally involve
modifying either the amplitude, the frequency or the phase of a sinusoidal RF carrier relative to changes in the
information signal.
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Introduction to Radio
AM (Amplitude Modulation)
In AM (Amplitude Modulation) systems, the amplitude of a sinusoidal carrier is altered relative to the amplitude of the
information signal.
The diagram illustrates a basic amplitude modulator with two inputs. One input is the information signal (in this case an
audio tone at 1 kHz), the second input is the carrier, e.g. 100 kHz. At the output of the modulator three frequency
components are present:
■■
the carrier, (fc) = 100 kHz
■■
a lower side frequency, (fc – fm) = 99 kHz
■■
an upper side frequency, (fc + fm) = 101 kHz
Irrespective of the modulation scheme used the information frequencies will appear alongside the carrier in the radio
spectrum. These translated frequency components are known individually as side frequencies, and collectively as side
bands.
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Modulation
AM (continued)
This diagram shows the 1 kHz audio tone, a 100 kHz RF carrier and subsequent amplitude-modulated waveform. With
reference to the modulated waveform, if the positive and negative peaks of the waveform are interconnected with a
dashed line, the exact shape of the modulating information signal (a 1 kHz audio tone) is recreated. The dashed line
shown on the modulated waveform is referred to as the envelope.
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DSB (Double Sideband) Modulation
The previous example used a single sinusoidal tone. In practical situations, however, the input to the modulator is likely
to be a complex signal, such as speech.
In this example, the output consists of a carrier plus two sidebands. Each component of the information signal
produces an upper and a lower side frequency within the respective sideband.
In this example, the output this form of modulation is DSB (Double Sideband) AM. It is used for radio broadcasting at
low and medium frequencies. The bandwidth of such a transmission can be computed by subtracting the highest
frequency in the upper sideband (USB) from the lowest frequency in the lower sideband, i.e:
3.6
Bandwidth = 103.4 kHz – 96.6 kHz = 6.8 kHz
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Modulation
FM (Frequency Modulation)
In an FM (Frequency Modulation) system the carrier has a constant amplitude and the carrier frequency is varied in
proportion to the amplitude of the information signal. The amount of change in carrier frequency from its nominal value
to either its minimum or maximum value is called the deviation. The total variation of the carrier from the lowest to the
highest frequency is termed carrier swing.
In FM, when a carrier is modulated, an infinite number of sidebands are created by each component (i.e. each
sinusoidal signal) in the information signal. The sidebands are separated by an amount equal to the modulating signal
frequency. Although not all the sidebands need be transmitted for acceptable quality in an FM system the bandwidth
occupied by an FM signal is generally much larger than an AM signal.
The diagram shows an RF carrier modulated by a sinusiodal modulating signal. As the signal goes positive, the
frequency of the carrier increases proportionally. The highest frequency change in the carrier occurs at the peak of the
information signal. As the information signal goes negative, the carrier frequency decreases. When the information
signal passes through zero the carrier frequency is at its nominal value, i.e. it is unmodulated.
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Radio Channels
Information can be converted to electrical signals and conveyed from one point to another using a transmission
medium. The transmission medium can be copper, fibre optic or a radio frequency carrier.
In a radio system a radio frequency carrier is assigned to a system and the information to be carried, for example
speech, is modulated onto the carrier and transmitted to the receiver.
Once the information has been modulated onto the RF carrier a new signal is produced in the RF spectrum. Depending
on the modulation process employed, this new signal will occupy a finite bandwidth.
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Modulation
Spectral Mask
The spectrum space allocated must be sufficient to contain the bandwidth of the signal.
This space is known as the channel, or channel space, with the carrier being the centre or identifying frequency.
Regulatory authorities produce spectral mask diagrams for radio channels. Manufacturers need to ensure that the
spectrum radiated from their equipment fits within the limits of the spectral mask.
When both receivers and transmitters are tuned to this centre frequency and the respective input and output filters
have the requisite bandwidth capabilities, no more, no less, then a reliable and accurate channel is realised.
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SECTION 4
RADIO SPECTRUM
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CONTENTS
Social and Economic Benefits of Spectrum . . . . . . . . . 4.1
WRC (World Radio Conference) . . . . . . . . . . . . . . . . . 4.8
UK Research – November 2012 . . . . . . . . . . . . . . . . . 4.2
CEPT (European Conference of Postal and
The Radio Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3
Telecommunications Administrations) . . . . . . . . . . . . 4.9
‘Step’ Changes in Telecommunications . . . . . . . . . . . . 4.4
ECO (European Communications Office) . . . . . . . . . 4.10
Radio Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5
Ofcom (Office of Communications) . . . . . . . . . . . . . . 4.11
The ITU-R (International Telecommunication Union –
Spectrum Management within the UK – Ofcom . . . . 4.12
Radiocommunications Sector) . . . . . . . . . . . . . . . . . . 4.6
Licensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13
Frequency Allocation . . . . . . . . . . . . . . . . . . . . . . . . . 4.7
Licence Exemption . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14
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Social and Economic Benefits of Spectrum
The above mentioned stories highlight the positive impact that mobile telephony has had on both developed and
developing nations.
The advent of true mobile broadband, and the associated sophisticated applications and services, has coupled the
benefits of broadband with those of mobility.
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UK Research – November 2012
On 5 November 2012 the UK Government published a report entitled:
“Impact of radio spectrum on the UK economy and factors influencing future spectrum demand”
*
A number of the key findings are listed above, reinforcing the view that, as time passes, the economic benefits of
spectrum continue to increase.
*
http://www.culture.gov.uk/publications/9498.aspx
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Radio Spectrum
The Radio Spectrum
The diagram illustrates the electromagnetic spectrum and indicates the portion occupied by radio systems.
Radio systems are identified by the frequency or wavelength of operation.
The radio spectrum is subdivided into a number of bands, which are listed in full below.
Very Low Frequency (VLF)
Low Frequency (LF)
Medium Frequency (MF)
High Frequency (HF)
Very High Frequency (VHF)
Ultra High Frequency (UHF)
Super High Frequency (SHF)
Extra High Frequency (EHF)
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–
–
–
–
–
–
–
10–30 kHz (Long wave)
30–300 kHz (Long wave)
300–3000 kHz (Medium wave)
3–30 MHz (Short wave)
30–300 MHz
300–3000 MHz
3–30 GHz (Microwaves)
30–300 GHz
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‘Step’ Changes in Telecommunications
There have been many ‘step’ changes in telecommunications technology over the last 170 years. The most significant
are listed above, with the advent of true mobile broadband being the most recent.
The detail behind the technologies that enable such developments is almost irrelevant; what is important is recognising
that each development in radio technology places an additional demand on the finite resource that is the radio
spectrum.
It is interesting to note that the International Telegraph Union was formed in 1865, prior to the invention of the
telephone. Even at this early date in the evolution of telecommunications it was realised that some form of international
co-operation was required.
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Radio Spectrum
Radio Services
It is also important to realise that, over time, technological developments always impact a wide range of ICT services.
Here we are considering those services which utilise radio spectrum, particularly those available to the general public
via commercial fixed and mobile radio operators. However, it is not wise to consider these services in isolation; the
spectrum is utilised by a wide range of radio services. A range of radio services are listed above and all are making
ever increasing demands on this valuable, but finite, resource.
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The ITU-R (International Telecommunication Union – Radiocommunications Sector)
With so many services and so many users, it is necessary to manage the radio spectrum and regulate both the
services and users. This is done at three levels, globally, regional and nationally.
The International Telegraph Union, as the ITU was formerly known, was founded in 1865 to standardize rules and
equipment to interconnect differing telegraph systems within Europe.
The CCIR – Comité Consultatif International pour la Radio, Consultative Committee on International Radio or
International Radio Consultative Committee – was founded in 1927.
In 1932 the CCIR and several other organizations (including the original ITU) merged to form what would in 1934
become known as the International Telecommunication Union. In 1992, the CCIR became the ITU-R.
Today, as a specialized agency of the United Nations, the ITU coordinates the shared global use of the radio spectrum,
promotes international cooperation in assigning satellite orbits and establishes worldwide standards for
communications systems. For the purposes of allocation the ITU-R considers the world as divided into three Radio
Regions as illustrated above.
The ITU is based in Geneva, Switzerland, and is divided into three ITU Sectors and ITU Telecom.
■■
ITU-R (Radiocommunication)
■■
ITU-T (Standardization)
■■
ITU-D (Development)
■■
ITU Telecom
The Radiocommunication Sector is concerned with radio communications at a global level. Details about the other
sectors can be found at http://www.itu.int
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Radio Spectrum
Frequency Allocation
The ITU-R publishes the RR (Radio Regulations), which is an international treaty to which all the 192 ITU Member
States are bound. The Regulations include a Table of Frequency Allocations (Article 5 of the RR) that indicates which
types of services are allocated to the various parts of the radio spectrum. The Table divides the world into three radio
regions with services potentially allocated to different frequencies in those regions.
An allocation is defined by the ITU-R as an:
‘Entry in the Table of Frequency Allocations of a given frequency band for the purpose of its use by one or more
terrestrial or space radiocommunication services or the radio astronomy service under specified conditions. This term
shall also be applied to the frequency band concerned’.
The diagram illustrates the allocations for the 11.7–13.4 GHz band across the three radio regions.
Allocations can be specific; for example an allocation for a mobile service may be restricted to land mobile, which
excludes aeronautical and marine use.
In addition, allocations are either Primary or Secondary, where Secondary Services have no recourse to interference
from Primary Services. A Primary Service is indicated by the use of upper case letters.
ITU-R footnotes are appended to some of the allocations. The footnotes can refer to additional allocations, technical
parameters or other spectrum management issues. For example:
5.489 Additional allocation: in Peru, the band 12.1-12.2 GHz is also allocated to the fixed service on a primary basis.
5.493 The broadcasting-satellite service in the band 12.5-12.75 GHz in Region 3 is limited to a power flux-density not
exceeding –111 dB(W/(m² • 27 MHz)) for all conditions and for all methods of modulation at the edge of the service
area.
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WRC (World Radio Conference)
The WRC (World Radio Conference) is held every 3 to 4 years with the latest having taken place between 23rd
January and 17th February of 2012.
WRCs consider the results of the studies on options to improve the international spectrum regulatory framework based
on the effectiveness, appropriateness and impact of the Radio Regulations in respect of the evolution of existing,
emerging and future applications, systems and technologies. WRCs make decisions on the most profitable and
efficient ways to exploit the limited resource of radio frequency spectrum and manage satellite orbits, which will be
critical and increasingly valuable for the development of the global economy in the 21st Century.
WRCs also address any radiocommunication matters of worldwide character, instruct the Radio Regulations Board and
the Radiocommunication Bureau, and review their activities, determine the Questions for study by
Radiocommunication Assemblies and the Study Groups in preparation for future radiocommunication conferences.
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Radio Spectrum
CEPT (European Conference of Postal and Telecommunications Administrations)
CEPT was established in 1959 and its original members were monopoly-holding postal and telecommunications
administrations.
The work of CEPT was to promote cooperation on commercial, operational, regulatory and technical standardization.
This work has evolved and is now conducted by three autonomous business committees:
■■
ECC (Electronic Communications Committee)
■■
CERP (European Committee for Postal Regulation)
■■
Com-ITU (Committee for ITU Policy)
Of these three, it is the work performed by the ECC that has an impact on radio communications at a regional
European level.
Details about the other committees can be found at http://www.cept.org
The role of the ECC is to develop policies on electronic communications at a European level, taking into account
European and International legislation and regulations.
The ECC is also responsible for planning and harmonizing the efficient use of the radio spectrum and satellite orbits
within Europe to satisfy the requirements of users and industry.
The work performed by the ECC is done by a number of WGs, including:
■■
WG FM – Frequency Management
■■
WG RA – Regulatory Affairs
■■
WG SE – Spectrum Engineering
■■
WG CPG – Conference Preparatory Group
■■
WG NNA – Numbering, Naming and Addressing
The ECC is guided by a Steering Group or think tank and the European Communications Office (ECO).
Further details can be found at http://www.eco.dk
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ECO (European Communications Office)
The ECO was established in 2009 following the merger of the ERO (European Radiocommunications Office) and the
ETO (European Telecommunications Office).
The ECO is based in Copenhagen and its role is to support CEPT and its three committees by performing the following
functions:
■■
to be a centre of expertise in electronic communications
■■
to plan the future use of scarce resources
■■
to support the national frequency management authorities
■■
to perform consultations about specific parts of the radio spectrum
■■
to liaise with national authorities
The ECO website gives access to a number of online information systems including the DocDB (Document Database),
the EFIS (ERO Frequency Information System) and the ECA (European Common Allocation Table).
The ECA details strategies for the current and future use of radio spectrum in Europe and EFIS is an online frequency
information system where CEPT administrations publish their frequency allocations.
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Radio Spectrum
Ofcom (Office of Communications)
In the UK, Ofcom is responsible for all matters concerning radio.
Ofcom is the regulator for the UK communications industries. It has responsibility for television, telecommunications
and radio communications. Granted its powers on 29th December 2003, Ofcom inherited the duties of the five legacy
regulators listed above.
Ofcom is responsible for managing the radio spectrum in the UK and coordinates the interests of spectrum users,
including government and other interested parties. Ofcom represents the UK Government at meetings held with the
ITU-R, CEPT and ECO. Ofcom publishes the UK Frequency Allocation Table (UKFAT) which is available from the
Ofcom website.
Ofcom manages the spectrum in the UK through frequency planning, assignment and licensing, and keeping the
spectrum free .
Frequency Planning involves allocating different parts of the radio spectrum to particular radio services on a strategic
basis so that services do not interfere with each other.
Assignments made to individual users within the allocations and licensing systems are planned so that the spectrum is
used efficiently without interference from other users.
If harmful interference occurs, it is investigated and appropriate action is taken.
Further information can be obtained from Ofcom’s website, www.ofcom.org.uk.
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Spectrum Management within the UK – Ofcom
Until December 29th 2003, radio spectrum in the UK was managed by the RA (Radiocommunications Agency), an
executive agency of the Department of Trade. The role of the RA is now carried out by the Ofcom (Office of
Communications). More details about Ofcom can be found at their website:
http://www.ofcom.org.uk.
Ofcom produce the UK Frequency Allocation Table detailing how the spectrum and associated services are allocated
within the UK. It is available free of charge at:
http://stakeholders.ofcom.org.uk/binaries/spectrum/spectrum-information/UKFAT_2013.pdf
The diagram illustrates how the band 11.7–13.25 GHz is allocated within the UK.
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Radio Spectrum
Licensing
Users of radio services in the UK must (with one or two exceptions) be licensed.
Each Wireless Telegraphy licence issued by Ofcom under Section 1 of the Wireless Telegraphy Act 2006 authorizes the
licensee to establish and use a radio station or install or use equipment for wireless communications. The licence
details strict conditions, which are outlined below.
Although there are slight variations between individual licences, in general they all cover similar areas (see above).
Licences include a schedule giving further details such as transmit and receive frequencies, allowed range of
transmission, type of emission, output power and the type approval requirements.
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Licence Exemption
Not all types of radio equipment require the operator or user to obtain a licence. It would be extremely difficult and
expensive to administer a system whereby every remote car locking key fob user required a licence. The situation is
similar for domestic and commercial cordless telephones and radio controlled models. Such a system is unnecessary
where the equipment uses low power and is unlikely to cause interference to other radio systems.
Licence exemption is achieved by allocating parts of the spectrum to licence-free usage and by making regulations that
certain types of equipment may be used without licence, providing the general conditions set in the regulations are met.
These conditions may include common standards under which such equipment may be put freely on the market and
brought into use. These are often harmonised across Europe.
The need for this approach has grown over recent years with the advent of such technologies as Bluetooth™, Wi-Fi
and other, predominantly short-range, low-power radio systems.
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Introduction to Radio
SECTION 5
ANTENNAS AND TRANSMISSION
LINES
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Antennas and Transmission Lines
CONTENTS
Transmission Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3
Sample Antennas
Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5
Yagi – Broadcast Television Receive Antenna . . . . . 5.16
The Isotropic Radiator . . . . . . . . . . . . . . . . . . . . . . . . . 5.6
Broadband Satellite Receive Antenna . . . . . . . . . . . . 5.16
Inverse Square Law . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7
Broadcast Satellite Television Receive Antenna . . . . 5.17
The Half-Wave Dipole . . . . . . . . . . . . . . . . . . . . . . . . . 5.8
Communications Tower – TV Broadcast Antenna . . . 5.17
Polar Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.9
Communications Tower – 2 . . . . . . . . . . . . . . . . . . . . 5.18
Antenna Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10
Goonhilly – Satellite Communications . . . . . . . . . . . . 5.18
Transmit Power (ERP/EIRP) . . . . . . . . . . . . . . . . . . . . 5.11
Mobile Phone Mast – Tree . . . . . . . . . . . . . . . . . . . . . 5.19
Yagi Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.12
Mobile Phone Antenna – Camouflaged . . . . . . . . . . . 5.19
Yagi Radiation Patterns . . . . . . . . . . . . . . . . . . . . . . . 5.13
Mobile Phone Antenna – Where is it? . . . . . . . . . . . . 5.20
Microwave Antennas . . . . . . . . . . . . . . . . . . . . . . . . . 5.14
Microwave Radio Configurations . . . . . . . . . . . . . . . . 5.21
Other Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.22
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Antennas and Transmission Lines
Transmission Lines
A transmission line is a system for transferring electrical energy between two points, for example power cables or
telephone lines.
Coaxial cable is a transmission line and is used for connecting the antenna system to the equipment.
A signal travelling along the line must suffer the minimum amount of attenuation possible. This is important for both
transmit and receive paths.
The cable will consist of a central conductor surrounded by an insulating material called the dielectric. Around this will
be a screen of either braided copper wire or solid copper tubing. The whole is encased in a protective sheathing.
The methods of construction vary from manufacturer to manufacturer.
The central conductor may be a single copper or copper-plated aluminium strand, or a number of strands twisted
together for flexibility, or copper ‘tubing’.
The dielectric may be air with polythene spacers for support, polythene foam, or solid polythene.
If the outer screen is solid it will be corrugated to improve flexibility. The sheath, which has to be robust and watertight,
is usually PVC or polythene.
Each type has its advantages and disadvantages.
The engineer’s main concern is ensuring the selection of the correct feeder for the job.
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Transmission Lines
A coaxial cable consists of a central conductor surrounded by an insulating material called the dielectric. The central
conductor may be a single copper or copper-plated aluminium strand, or a number of strands twisted together for
flexibility, or copper ‘tubing’. The dielectric may be air with polythene spacers for support, polythene foam, or solid
polythene. If the outer screen is solid it will be corrugated to improve flexibility. The sheath, which has to be robust and
watertight, is usually PVC or polythene.
The simplest type of waveguide is a rectangular, air filled metal tube. The metal is often brass because it has good
mechanical rigidity and good electrical properties. Copper and sometimes silver is used to minimize losses. Aluminium
and other alloys can be used instead to reduce the weight. For practical reasons the waveguide is supplied in fixed
lengths. To extend the length, pieces of waveguide can be joined together using flanges. Rectangular waveguide is
rigid making an installation difficult; however flexible waveguide is also available. It is made from a thin corrugated
rectangular spiral that is encased in rubber. This is useful for connecting an antenna to a microwave radio because it
allows some adjustment in the positioning of the antenna.
Elliptical waveguide is not as rigid as rectangular so it can be bent. However, it is recommended to consult the
manufacturer’s data sheet with regard to the bending radius. Couplers/adapters are available to connect to rectangular
waveguide.
Circular waveguide is most commonly used to couple two differently polarised signals to the same antenna.
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Antennas and Transmission Lines
Antennas
The antenna is the connecting link between free space and a transmitter or receiver.
All antennas have the same properties when transmitting and when receiving, i.e. the gain is the same, the radiation
patterns are the same, and the frequency of operation and beam width are the same.
No matter how good the transmitter or receiver is, a poor antenna will seriously limit the performance of a radio system.
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Introduction to Radio
The Isotropic Radiator
An isotropic radiator is a fictitious antenna. It radiates equally in all directions. It cannot be constructed, but is a useful
standard against which all other antennas can be compared. If such an antenna is placed in free space away from all
other influences, then the total radiated power will be spread over the surface of a sphere.
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Antennas and Transmission Lines
Inverse Square Law
The power intensity at a distance (d) will be proportional to the inverse of the square of the distance from the
transmitter. This is known as the inverse square law. This concept can be demonstrated using a light source as the
radiator (light, of course, is just a very high frequency electromagnetic wave).
The same amount of radiated energy must illuminate an ever-increasing area with increasing distance from the light
source. The area covered increases as the square of the distance; hence, the intensity of light per unit area decreases
as the square of the distance.
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Introduction to Radio
The Half-Wave Dipole
In free space, the velocity of an EM (Electro-Magnetic) wave is approximately 300,000,000 metres per second. This is
the speed of light (light is an EM wave) and is usually given by the symbol ‘c’. The relationship between ‘c’ (velocity), ‘ƒ’
(frequency) and ‘l‘ (wavelength) of an EM wave is given by the equation:
c=ƒxl
Where:
c = velocity of propagation in metres per second (3 x 108 metres per second)
ƒ = frequency in Hertz (Hz)
l = wavelength in metres (m)
The half-wave dipole is so called because it should be half a wavelength long at the transmitted frequency (or, more
practically, at the frequency in the centre of the band of frequencies on which transmission is to occur).
Such an antenna is said to be resonant at the transmit frequency and when this occurs it radiates with maximum
efficiency. If the antenna is greater or smaller than half a wavelength then the efficiency is reduced.
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Antennas and Transmission Lines
Polar Diagrams
The radiation pattern or polar diagram of an antenna displays the spatial distribution of the radiated energy. That is, the
direction in which the signal is transmitted or from where it is best received.
As can be seen from the diagram, no energy is radiated away from the ends of the antenna.
When mounted vertically, the antenna radiates omnidirectionally: it radiates equally well in all directions horizontally.
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Antenna Gain
Antenna gain is the result of the focusing action of a practical antenna, radiating more energy in one direction and less
in others.
The vertical l/2 dipole radiates equally well in all directions in the horizontal plane, but not in the vertical plane. In other
words, the radiated energy is focused in the horizontal direction.
Since a half-wave dipole directs more of the transmitted energy towards the horizontal plane, than an isotropic radiator,
it is said to have gain with respect to the isotropic radiator. The more directional the antenna is, the higher its gain.
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Antennas and Transmission Lines
Transmit Power (ERP/EIRP)
The radio licence stipulates the maximum transmitter power allowed. This power limit will be stated as either Effective
Radiated Power (ERP) or Effective Isotropic Radiated Power (EIRP).
ERP is calculated using the half-wave dipole as a reference antenna, EIRP is calculated using the isotropic radiator as
the reference.
The system designer will have a number of antenna types to choose from, all with different amounts of gain. The
designer must ensure that the power input to the antenna multiplied by the antenna gain does not exceed the licensed
maximum.
Antenna designers will publish gain figures for their antennas in respect of an isotropic, or a dipole, or both.
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Introduction to Radio
Yagi Antenna
The Yagi antenna adds more elements to the half-wave dipole, which are known as parasitic since they are not fed with
the signal from the feeder (connection between the transmitter/receiver and the antenna). There are two main types of
‘parasitic’ elements: reflectors and directors. The reflector element, as its name suggests, reflects the signal. It needs to
be longer than the half wave dipole and is placed behind the dipole to increase radiation in the required direction. This
antenna has one main element (half-wave dipole) and one reflecting element. The distance between the dipole and the
reflector is very important.
Director elements can be added to this antenna to increase the gain in the required direction. The directors are
generally smaller than the main element.
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Antennas and Transmission Lines
Yagi Radiation Patterns
The diagram illustrates typical Yagi radiation patterns. Note the focussing of energy (gain) compared to the dipole, and
the side and rear lobes.
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Introduction to Radio
Microwave Antennas
The antenna generally employed at microwave frequencies is the parabolic reflector. This type of antenna consists of a
large reflecting surface, the geometry of which is parabolic, thus creating a focal point from which energy can be fed to
illuminate the dish. When receiving signals, the parabola concentrates energy on the focal point.
The diagram illustrates the importance of the antenna geometry. Energy illuminating the reflector from the focal point
will create a parallel wavefront in front of the dish. This form of antenna is to be found employed in microwave line-ofsight (LoS) systems for both terrestrial and satellite applications.
Yagi – Broadcast Television Receive Antenna
Broadband Satellite Receive Antenna
Broadcast Satellite Television Receive Antenna
Communications Tower – TV Broadcast Antenna
Communications Tower – 2
Goonhilly – Satellite Communications
Mobile Phone Mast – Tree
Mobile Phone Antenna – Where is it?
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Introduction to Radio
SAMPLE ANTENNAS
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Yagi – Broadcast Television Receive Antenna
Broadband Satellite Receive Antenna
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Antennas and Transmission Lines
Broadcast Satellite Television Receive Antenna
Communications Tower – TV Broadcast Antenna
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Communications Tower – 2
Goonhilly – Satellite Communications
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Antennas and Transmission Lines
Mobile Phone Mast – Tree
Mobile Phone Antenna – Camouflaged
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Mobile Phone Antenna – Where is it?
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Antennas and Transmission Lines
Microwave Radio Configurations
Traditionally with microwave systems, all the hardware was placed in a self-contained hut or cabinet at the foot of the
mast and the RF output travelled up the mast via a waveguide.
However, with more reliable systems and large scale integration, Split Outdoor Units (ODUs) have become very
common, mixing down the RF to IF, or even performing complete demodulation to baseband. In these circumstances
coaxial lines may be used, with a short length of flexible waveguide connecting the ODU to the antenna.
Further technological developments have allowed the manufacture of complete ODUs, with the antenna being slip
fitted directly to the transceiver, and baseband data (Ethernet) being delivered directly to the transmission network via
co-axial cable.
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Other Antennas
Yagi antennas are generally used when the frequency of operation is too low to allow realisation of a practical parabolic
antenna. For example, they are used extensively on 400 MHz telemetry systems.
Grid antennas are also used at lower microwave frequencies. The antenna has exactly the same electrical
performance characteristics as a solid parabola. However, the front to back ratio is generally lower because of the
diffraction of RF energy around the bars of the grid structure. Also, they only support one plane of polarisation due to
the plane of the grid structure. An advantage of this method of construction is that grid antennas have excellent cross
polar discrimination properties. They also have very low wind loading properties.
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Introduction to Radio
SECTION 6
PROPAGATION
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Propagation
CONTENTS
Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1
Daytime Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7
The VLF (Very Low Frequency) Band . . . . . . . . . . . . . 6.2
Night-time Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 6.8
The LF (Low Frequency) Band . . . . . . . . . . . . . . . . . . 6.3
The HF (High Frequency) Band . . . . . . . . . . . . . . . . . 6.9
The MF (Medium Frequency) Band . . . . . . . . . . . . . . . 6.4
VHF (Very High Frequencies) and Above
The Ionosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5
(UHF, SHF and EHF) . . . . . . . . . . . . . . . . . . . . . . . . . 6.10
Antenna Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6
Space Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.11
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Propagation
Propagation
Propagation describes the way that radio waves travel between a transmitter and a receiver, or receivers, at some
distant point.
As stated previously, a radio wave is electromagnetic energy, which propagates through free space at the speed of light
(300,000,000 metres/sec).
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The VLF (Very Low Frequency) Band
In this band, the radio wave follows the curvature of the earth’s surface and is therefore known as a ground, or surface,
wave.
Given sufficient transmitter output power and large antenna arrays, very-long-range communication is possible, up to
5,000 kilometres.
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Propagation
The LF (Low Frequency) Band
In this band, the radio wave again follows the curvature of the Earth’s surface, so it is a ground or surface wave.
However, because the frequency is now higher, the radio wave is attenuated by the Earth more quickly, meaning that
the effective range of communication is reduced to one or two thousand miles, depending upon transmitter output
power.
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The MF (Medium Frequency) Band
In the MF band the radio wave is again ground/surface wave, but because the transmit frequency is increased, the
range of communication is further reduced. This attenuation in signal strength occurs because as frequency increases,
the earth absorbs more energy.
The range of communication now depends on the transmitter power output and the type of signal being transmitted.
The greater the bandwidth the shorter the range. Figures vary, but could range from 100 to 500 km.
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Propagation
The Ionosphere
The ionosphere is another factor affecting MF propagation. The ionosphere is a region of ionised particles 50–500 km
above the earth’s surface. It exists due mainly to radiation from the sun, but also to cosmic radiation from space.
The overall average density of ionisation will change due to a number of factors. As the sun moves across the sky
during daytime, the level of radiation and therefore ionisation, changes; and at night the sun is around the other side of
the earth and so the radiation is minimal and so is the level of ionisation. Also, the ionisation varies between spring,
summer, autumn and winter and the 11.1-year sun spot cycle affects the level of ionisation.
During daytime, the ionosphere tends to form itself into four layers (D, E, F1 and F2). These are peaks in the level of
ionisation. During the night, the peaks in ionisation fall and the layers combine into E and F layers.
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Antenna Radiation
It has been shown that depending on the antenna type and construction, an antenna may display the property of gain.
The antenna may radiate in both the horizontal and vertical planes to a more or lesser degree.
This means that while some energy may travel through free space (following the curvature of the earth), some may
also be directed towards the ionosphere.
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Propagation
Daytime Conditions
On medium frequency during daytime, communication is by ground wave only. Components that enter the ionosphere
are absorbed and therefore lost.
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Night-time Conditions
Compared to daytime conditions, there are now only two layers in the ionosphere with different densities. The result is
that components of the MF signal entering the ionosphere are refracted (bent) to such an extent that they return to
earth. These waves are known as sky waves. This greatly increases the range of communications at night such that at
night it could be four or five times greater than during the day.
There is an area where ground/surface waves and sky waves can be received at the same time. This often causes
problems because when the two signals are received, they may or may not be in-phase and will tend to partially, or in
some cases totally, negate each other. This is caused by the waves travelling different distances before they reach the
receive antenna. Also, the ionosphere is a very unstable medium, which often causes changes to both the amplitude
and phase of the sky waves. As a result, the received signal tends to fade in and out and become distorted.
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Propagation
The HF (High Frequency) Band
In the HF band the ground/surface wave component, being high in frequency, is attenuated by the earth very quickly
after leaving the transmit antenna. The ground/surface wave is therefore ignored.
As a high-frequency signal enters the ionosphere it is refracted sufficiently to return to earth. However, the higher the
frequency, the less the refraction, so that frequencies around, say, 4 MHz are refracted sharply and return to earth
quickly, while the higher frequencies need to pass further through the ionospheric layers before they finally undergo
sufficient refraction to return to earth.
Higher HF frequencies tend to come back to earth at a greater distance than lower ones. Although the ionosphere may
attenuate the signals, the higher the frequency is, the less the attenuation will be. It is not unusual for the signals to
return to earth, reflect off the surface and re-enter the ionosphere such that the higher frequency signals bounce (multihop) around the earth over varying distances.
The range achieved by HF communication is typically between 10 and 10,000 kilometres.
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VHF (Very High Frequencies) and Above (UHF, SHF and EHF)
These frequencies are above about 30 MHz, where the wavelength becomes very short. Towards the top of the UHF
band, the term microwaves is used. At these frequencies, the ground wave is again negligible, being absorbed very
rapidly. Sky waves tend to escape into space because of the different properties of the ionosphere at these
frequencies. This allows satellite relays to be used, extending the range well over the horizon.
Low-angle radiation from the antenna propagates as space waves.
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Propagation
Space Waves
The space wave travels in the lower atmosphere (known as the troposphere) and is generally said to follow a LoS (Line
of Sight) path. This does not mean that the waves travel in a straight line – they are in fact refracted in the troposphere,
meaning that the radio horizon is significantly greater that the geometric horizon. Under standard tropospheric
conditions, ranges of tens of kilometres are normal, increasing with antenna height.
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SECTION 7
RADIO COVERAGE
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CONTENTS
Radio Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1
Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4
Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2
Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5
Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3
Tropospheric Anomalies . . . . . . . . . . . . . . . . . . . . . . . 7.6
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Radio Coverage
The general rule of propagation with VHF and UHF frequencies is that the range is limited to the horizon, because
radio waves at these frequencies propagate in the LoS.
However, within this distance there is a loss of signal strength in proportion to the distance from the transmitter. This
loss increases with the frequency, hence it limits range.
At VHF frequencies, this loss is generally not a problem, but with UHF frequencies it can limit the range to somewhat
less than the horizon, especially at low power levels.
Nevertheless, with the power levels typically used in land mobile communications, good communication conditions can
normally be expected within the LoS.
Hills, mountains, chimneys, large buildings, etc. are often in the way of radio waves. They absorb, reflect and diffract
these waves, sometimes in an unwanted manner.
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Reflection
Reflection occurs when the wave impacts a relatively smooth surface. The wave is reflected with an angle of reflection
equal to the angle of incidence and with a strength dependent upon the conductivity of the reflector. The greater the
conductivity, the stronger the reflection.
This type of reflection is often termed specular.
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Radio Coverage
Scattering
Scattering occurs when a wave reflects off a rough surface. The degree of scatter depends on the roughness of the
surface relative to the operating wavelength. This is sometimes termed diffuse reflection.
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Diffraction
Diffraction occurs when a wave passes over an edge of an object, with the degree of defraction increasing with
frequency.
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Radio Coverage
Attenuation
Attenuation is caused by any object obstructing the path of the wave. Once again, this tends to increase with
frequency.
The value of attenuation will depend upon a number of factors including operating wavelength, the dimensions of the
object and the materials from which it is made.
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Tropospheric Anomalies
Like the ionosphere, the troposphere is subject to change. Here, the changes are due to changes in temperature,
barometric pressure and humidity at various altitudes. The result of these variations is that the amount of refraction
varies with a consequent change to the radio signal path. There are three effects of this: subrefraction, super-refraction,
and ducting.
Sub-refraction causes the range of the radio horizon to be reduced and tends to occur in the polar regions.
Super-refraction causes an increase in the radio horizon up to 100–200 kilometres and tends to occur in tropical
regions.
Ducting is an extreme case of super-refraction. Ducting occurs as the refracted wave reflects from the Earth’s surface
and extreme range increases of several hundred kilometres can occur. This is known to occur in the Persian Gulf and
Red Sea areas and, on occasion, around the UK.
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Introduction to Radio
SECTION 9
RADIO INTERFERENCE
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Radio Interference
CONTENTS
Co-Channel Interference . . . . . . . . . . . . . . . . . . . . . . . 8.1
Frequency Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4
Adjacent Channel Interference . . . . . . . . . . . . . . . . . . 8.2
Anomalous Weather Conditions . . . . . . . . . . . . . . . . . 8.5
Illegal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3
Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6
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Radio Interference
Co-Channel Interference
Any communication system that relies on a radio link has a large number of problems to overcome to make the system
work reliably and with maximum quality. The biggest problem is interference, which is due to a number of causes.
Channel interference occurs when the receiver receives signals from other transmitters on the same channel or
frequency. This is minimised by having a large reuse distance, i.e. transmitters placed geographically apart.
The diagram illustrates a situation where a radio broadcast receiver in a vehicle is receiving a wanted radio carrier from
a transmitter and is also suffering co-channel interference from another transmitter operating on the same channel.
This causes interference and as the vehicle moves closer to the unwanted signal transmitter it may become ‘locked’
onto that signal.
Co-channel interference also occurs on MF and HF bands from hundreds of kilometres via sky waves.
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Introduction to Radio
Adjacent Channel Interference
This is caused by signals adjacent to each other on the radio spectrum being received simultaneously. This is
minimised by adequate channel spacing or by improving the selectivity of the receiver, i.e. its ability to pick out the
wanted signal and reject all others.
Adjacent channel interference occurs when a radio tuned to a particular channel fc suffers interference from an
adjacent channel fc - 1 or fc + 1. Although the radio is not actually tuned to the adjacent channel, it may still receive a
weaker signal from it, allowing the adjacent channel to interfere with the wanted channel to which the radio is tuned.
The more selective the receiver is, the less will be its response to adjacent channels.
The strength of the wanted channel to that of the adjacent channel is expressed by the Carrier to Adjacent Channel
(C/A) Ratio.
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Radio Interference
Illegal Operation
This type of interference is usually easy to identify, but often difficult to trace. Pirate radio stations are probably the
most familiar source of such interference. The allocation of spectrum for community radio broadcasting has had some
positive impact on the reduction of the number of pirate stations. However a significant number do exist, some as a
cover for other illicit operations. Other examples of illegal operation are many and varied e.g. mobile phone blockers,
transmitting to aircraft pilots, and operating radio systems without a licence.
The field engineering functions within Ofcom have the technical equipment and skills required to trace interference
sources and can legally pursue avenues to close down transmission, seize equipment or material and prosecute for
illegal usage.
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Introduction to Radio
Frequency Planning
Frequency allocation takes place in the international and national arenas. The licensing of systems takes place at the
national level. In the UK Ofcom assigns spectrum to users as part of the licence issuing process. Some users will be
assigned a single channel at the discretion of Ofcom. In these cases frequencies are assigned in accordance with a
national frequency plan produced by Ofcom. This frequency plan will minimise the likelihood of any co-channel
interference.
Licences are also issued to system network operators e.g. the mobile phone operators. Blocks of spectrum are
assigned to these operators and the frequency planning process is the responsibility of the licensed operator. The
initial resolution of interference experienced by the operators is the responsibility of the licensed operator. If the
operator believes the interference is emanating from outside their network they can then contact Ofcom for help in
pursuit of the interference source.
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Radio Interference
Anomalous Weather Conditions
Atmospheric conditions affect radio propagation. Occasionally, conditions arise that cause radio energy to propagate
distances far in excess of the planned coverage area. Stories abound of such instances such as New York taxi cab
radio being picked up in the UK and the Marseille Police received on Cumbria County Council radios. There is not
much that engineers can do under these circumstances; they just have to wait for the weather to change.
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Introduction to Radio
Noise
Noise in telecommunications is generally defined as any unwanted signal which appears with the wanted signal at a
point of measurement. Specifically, noise produces an unintelligible output from the receiver. There are many sources
of noise which are either external to the system or the product of internal elements.
The receiver antenna picks up not only the desired signal but also electromagnetic radiation created by lightning and
electrical discharge between clouds (referred to as static), by solar flares on the sun and by violent outbursts on other
stars in galactic space. These causes are known as naturally occurring noise.
Man-made radiation is usually caused by couplings from such things as power lines, motors, neon signs, light flashers
and dimmers, vehicle ignition, medical apparatus, industrial equipment, switched power supplies, computers and, of
course, other radio systems.
In theory, undesired non-random signals can be eliminated by the application of proper suppression techniques as
close to the source as possible.
An important measure of quality for analogue systems is the SNR (Signal-to-Noise Ratio). The higher the ratio, the
better the quality of received signal.
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Introduction to Radio
SECTION 9
ANALOGUE AND DIGITAL
SYSTEMS
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Analogue and Digital Systems
CONTENTS
Analogue and Digital Signals . . . . . . . . . . . . . . . . . . . . 9.1
Digital Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7
Digital Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2
Data Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.8
Analogue Signal Quality . . . . . . . . . . . . . . . . . . . . . . . 9.3
Square Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.9
Digital Signal Quality . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4
Complex Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.10
Integrated Services . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5
ASK (Amplitude Shift Keying) . . . . . . . . . . . . . . . . . . . 9.11
Analogue to Digital Conversion . . . . . . . . . . . . . . . . . . 9.6
FSK (Frequency Shift Keying) . . . . . . . . . . . . . . . . . . 9.12
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Analogue and Digital Systems
Analogue and Digital Signals
Most of the signals considered so far have all been analogue signals. However, most telecommunications systems are
now based on digital technology.
An analogue signal has an infinite range of amplitude values in respect of time, which is continuous, whereas a digital
signal has a discrete limited range of amplitude values in respect of time, which is discontinuous.
The term data is often used when people talk about digital technology; but what is data? The literal meaning of the
word is simply ‘information’. However, in this context it means information which is conveyed in a digital form.
It should be noted that information itself may well be analogue. Modern telephony, music and television are examples
of analogue information (speech, music and moving pictures) that is converted to a digital form.
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Introduction to Radio
Digital Systems
All modern telecommunication networks are digital. The benefits of digital networks include quality improvements and
the integration of different services onto one network.
Information, such as speech, does not originate as a digital signal – it is analogue. The process of digitization –
conversion from analogue to digital – will be performed as close to the point of origin as possible. In a fixed telephone
network, this would be at the local exchange. For a digital mobile network, it takes place in the handset.
9.2
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Analogue and Digital Systems
Analogue Signal Quality
In any electronic environment, whether it is a piece of equipment or a link between equipment (cable or radio), there
will be random signals present referred to collectively as ‘noise’. This noise may originate from several sources but is
always present to a greater or lesser degree. Once noise becomes mixed with an analogue signal, the two components
(noise and signal) can never be fully separated. This means that any attempt to amplify an attenuated (diminished)
analogue signal will amplify not only the wanted signal, but noise as well. Hence over any transmission path the quality
of an analogue signal will continuously degrade.
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Digital Signal Quality
Digital signals also become corrupted by noise. However, it is a relatively simple process to remove the noise by
regenerating the digital waveform.
Although a clean digital bit stream is transmitted, it becomes corrupted by noise along the transmission link to its
destination. The receiver examines each individual bit as it arrives and interprets its value in relation to a threshold
value. For example, if the value is above the threshold, the value will be interpreted as a logical ‘1’, and if it is below the
threshold, it will be interpreted as a logical ‘0’. Assuming the correct decision is made, the digital bit stream may then
be regenerated to its original noise-free form.
If the signal is pushed too far along the transmission medium without regeneration, the received waveform will be so
corrupt that the system will be unable to recognise it. During transmission, therefore, the signal needs to pass through
a regenerator before it becomes too corrupt.
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Analogue and Digital Systems
Integrated Services
The reasons for the move from analogue to digital within the telecommunications industry include better quality and
integrated services.
All types of communication can be treated in the same way and information can be transmitted and processed by a
common (integrated) network. This reduces the cost of building and maintaining the network.
In addition, other information crucial to the operation of a complex network, such as signalling and network
management, can travel on common shared channels.
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Introduction to Radio
Analogue to Digital Conversion
A number of techniques exist for the conversion of analogue signals into a digital format. The diagram above illustrates
a simplified version of one such method: PCM (Pulse Code Modulation).
The analogue signal is sampled (a). The amplitude of each sample is given a decimal value or quantity – quantization
(b).
Each amplitude value is then converted from decimal to binary – this is the coding (c). The binary numbering scheme
has only two values, 0 and 1. The key to the code is the series of decimal numbers, commencing with 1 (one), each
subsequent number being the previous number doubled i.e. 2, 4, 8, 16, 32 etc.
9.6
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Analogue and Digital Systems
Digital Signals
Digital signals are streams of data bits, where a bit (‘bit’ being a contraction of BInary digiT) is normally one of two
states, either a ‘1’ or a ‘0’. Most modern radio systems are digital and even analogue signals such as speech and
television images can be represented in a digital format.
When a digital signal is transmitted in a system, an important characteristic is the data rate. This is measured or
expressed in bits per second (bits/s). For high data rates it is common to use the following prefixes:
■■
kilobits/s (kbit/s)
[1 kbit/s = 1,000 bit/s]
■■
Megabits/s (Mbit/s)
[1 Mbit/s = 1,000,000 bit/s]
■■
Gigabits/s (Gbit/s)
[1 Gbit/s = 1,000,000,000 bit/s]
In general terms, the higher the data rate in a digital system the greater the resulting bandwidth of a radio signal
created from that data. (In other words, it requires more spectrum).
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Introduction to Radio
Data Rates
The time taken to transmit and receive data is dependent upon the capacity of a network and, if a radio system, on the
spectrum bandwidth allocated.
The higher the data rate of a system, the shorter the time taken to transmit and receive the data. Where services are
offered using radio systems, sufficient spectrum bandwidth must be allocated to provide a data rate which satisfies the
speed requirements of the service. For example, waiting 33 minutes to download a short video clip would be
unacceptable.
The diagram shows the data rates of various telecommunication systems and the length of time it takes to receive
different types of information, assuming no system delays and no inclusion of additional data.
9.8
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Analogue and Digital Systems
Square Waves
A square wave has a periodic variation, known as frequency, just like a sine wave. Although the square wave has a
periodic variation it is a complex wave, not a pure sine wave. The French mathematician Baron Jean Baptiste Joseph
Fourier (1768–1830) determined that any complex wave can be broken down into individual sinusoidal signals (the
frequency domain) that make up the wave shape (the time domain). This is also known as the ‘Fourier Analysis’.
The harmonic relationship between the fundamental square wave frequency (f) and the individual sinusoidal
components that make this square wave shape is interesting. The frequencies are all odd multiples, 3xf, 5xf and 7xf
Figure b) only shows the first four components. A square wave is made up of an infinite number of odd harmonics of
the fundamental ever decreasing in amplitude. Figure b) only shows the first four components.
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Introduction to Radio
Complex Waves
Any complex wave (not sinusoidal) comprises a number of sinusoidal signals. The frequency components are
harmonically related to the fundamental frequency of the complex wave.
The bandwidth (frequency domain) of any signal is related to the shape of the signal (time domain).
The ‘shape’ of the waveform is most often construed as the ‘information’. It is the sum of the individual frequency
components that produces the shape.
9.10
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Analogue and Digital Systems
ASK (Amplitude Shift Keying)
The simplest digital modulation formats are ASK (Amplitude Shift Keying) and FSK (Frequency Shift Keying).
Whichever format is used, the goals are the same: high spectral efficiency, narrow power spectrum and resilience to
the hostile radio environment.
Amplitude shift keying, shown here, is an elementary form of modulation that goes back to the earliest days of radio as
does the term keying (the carrier amplitude is switched manually using a switch called a key).
In this type of modulation, one of the binary states (a logic ‘1’, say) corresponds to high carrier amplitude and the other
binary state (a logic ‘0’, say) corresponds to low carrier amplitude.
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Introduction to Radio
FSK (Frequency Shift Keying)
Until recently, FSK was the most widely used form of digital modulation, being both simple to generate and to detect.
FSK conveys the data using distinct carrier frequencies to represent logic ‘1’ and logic ‘0’. Logic ‘1’ is represented by a
high carrier frequency and logic ‘0’ by a low carrier frequency. The bandwidth of an FSK signal is harder to determine
than in an ASK signal, as it depends on the separation of the frequencies representing a logic ‘1’ and a logic ‘0’.
The bandwidth used by FSK will generally be greater then that of an ASK signal.
9.12
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INTRODUCTION TO RADIO
GLOSSARY OF TERMS
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Introduction to Radio
G.2
3 GPP
3rd Generation Partnership Project
AM
ASK
Amplitude Modulation
Amplitude Shift Keying
CCIR
CEPT
CERP
Com-ITU
Comite Consultatif International pour la Radio, Consultative Committee on
International Radio, or International Consultative Committee
European Conference of Postal and Telecommunications Administration
European Committee for Postal Regulation
Committee for ITU Policy
DSB
DocDB
Double Sideband Modulation
Document Database
ECA
ECC
ECO
EFIS
EHF
EIRP
EM
ERO
ERP
ETO
European Common Allocation Table
Electronic Communications Committee
European Communication Office
ERO Frequency Information System
Extra High Frequency
Effective Isotropic Radiated Power
Electro-Magnetic
European Radio Communications Office
Effective Radiated Power
European Telecommunications Office
FM
FSK
Frequency Modulation
Frequency Shift Keying
HF
High Frequency
ITU
ITU-D
ITU-R
ITU-T
International Telecommunications Union
ITU-Development
ITU-Radio Communication Sector
ITU-Telecommunication Standardization Sector
LED
LF
LoS
Light Emitting Diode
Low Frequency
Line of Sight
MF
Medium Frequency
Ofcom
Office of Communications
PCM
PSTN
Pulse Code Modulation
Public Switched Telephone Network
RF
RR
Radio Frequency
Radio Regulations
SHF
NR
Super High Frequency
Signal-to-Noise Ratio
USB
UHF
UKFAT
Upper Sideband
Ultra High Frequency
UK Frequency Allocation Table
VHF
VLF
Very High Frequency
Very Low Frequency
WRC
WG
WG FM
WG RA
WG SE
WG CPG
WG NNA
World Radio Conference
Working Group
Working Group Frequency Management
WG Regulatory Affairs
WG Spectrum Engineering
WG Conference Preparatory Group
WG Numbering, Naming and Addressing
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RP1302/v1.0
your quick guide to telecoms training
Category
Code
Level
Duration
Small Cell Technologies
Small Cell Overview.....................................................................LT1319.............. 1...............1 hour
LTE SON and Small Cell Deployment..........................................LT1320.............. 2...............2 hours
Small Cells Engineering Overview...............................................LT1311.............. 2...............1 day
Small Cells - Technologies and Markets......................................LT1304.............. 2...............1 day
Small Cell Backhaul Connectivity.................................................LT1321.............. 3...............1 day
Flexible delivery options
LTE
LTE – The 4G Solution.................................................................ELT1001........... 1...............1 hour
Understanding 4G LTE.................................................................ELT1317........... 1...............0.5 hours
LTE Technologies, Services and Markets....................................LT3601.............. 1...............1 day
Essential LTE...............................................................................ELT1002........... 2...............4 hours
LTE Engineering Overview...........................................................LT3600.............. 2...............2 days
LTE Advanced..............................................................................LT1318.............. 2...............1 day
Single RAN . ................................................................................LT1203.............. 2...............1 day
Mobile Backhaul for 3G and 4G Networks...................................TY1201............. 2...............2 days
LTE Backhaul...............................................................................LT1202.............. 2...............1 day
LTE RAN Capacity Planning........................................................LT1322.............. 2...............3 days
LTE Backhaul Planning................................................................LT1312.............. 2...............1 day
LTE Evolved Packet Core Network..............................................LT3604.............. 3...............2 days
LTE EPC Signalling......................................................................LT1309.............. 3...............1 day
LTE Radio Access Network..........................................................LT3603.............. 3...............2 days
LTE RAN Signalling......................................................................LT1308.............. 3...............1 day
LTE Air Interface...........................................................................LT3602.............. 3...............3 days
LTE Air Interface Signalling..........................................................LT1307.............. 3...............1 day
LTE End-to-End Signalling...........................................................LT1301.............. 3...............2 days
LTE Signalling and Operations.....................................................LT1310.............. 3...............0.5 days
LTE Voice Options and Operations..............................................LT1002.............. 3...............2 days
LTE Voice – CS Fallback..............................................................LT1002CS......... 3...............1 day
LTE Voice – VoLTE.......................................................................LT1002VO........ 3...............1 day
LTE Voice – RCS.........................................................................LT1323.............. 3...............1 day
Cell Planning for LTE Networks...................................................LT2901.............. 3...............2 days
LTE Optimization..........................................................................LT1001.............. 3...............2 days
LTE Administration.......................................................................LT1313.............. 3...............2 days
LTE Security.................................................................................LT1303.............. 3...............0.5 days
LTE Quality of Service..................................................................LT1314.............. 3...............1 day
LTE Policy and Charging..............................................................LT1315.............. 3...............0.5 days
LTE Billing and Charging..............................................................LT1316.............. 3 ..............0.5 days
LTE Air Interface Specialist Workshop.........................................LT1302.............. 3+.............1 day
Training can be delivered in a variety
of formats to meet individual and
operational needs.
These include:
▪▪ instructor-led training through open
courses
▪▪ instructor-led training through closed
courses
▪▪ online virtual classroom training
▪▪ workshops
▪▪ e-Learning hosted on your Learning
Management System (LMS) or
supplied on CD
▪▪ technical briefings
▪▪ ‘brown bag’ sessions
▪▪ videos developed to customer
requirements
IP Networks and Protocols
IP Convergence Essentials..........................................................IP1301.............. 1...............1 day
IP/Ethernet Essentials..................................................................IP1302 ............. 1...............1 day
IP Services Essentials..................................................................IP1303.............. 1...............1 day
Internetworking, Ethernet LANs and VLANs Principles...............IP1304.............. 2...............1 day
IP Addressing and Internet Protocols Principles..........................IP1305.............. 2...............1 day
IPv6 System Overview.................................................................IP1101.............. 2...............1 day
Multi Protocol Label Switching.....................................................IP1307.............. 2...............1 day
Quality of Service Principles........................................................IP1308.............. 2...............1 day
Routing Protocol Principles..........................................................IP1306.............. 2...............2 days
IP Multicast Routing.....................................................................IP1311.............. 3...............2 days
MPLS VPNs and Traffic Engineering...........................................IP1312.............. 3...............2 days
OSPF and BGP Routing Protocols..............................................IP1310.............. 3...............2 days
Quality of Service (QoS)..............................................................IP1309.............. 3...............2 days
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your quick guide to telecoms training
Category
Code
Level
Duration
IP Networks and Protocols (continued)
Technical levels
Level 1 Courses
IP Engineering..............................................................................IP2300.............. 2...............2 days
Cloud Computing.........................................................................WR1201........... 2...............1 day
IP Workshop.................................................................................IP2900.............. 3...............5 days
TCP/IP..........................................................................................QS2501............ 3...............2 days
Softswitching and VoIP................................................................IP2001.............. 3...............2 days
NGN Voice Protocols...................................................................TY1202............. 3...............3 days
SIGTRAN.....................................................................................QS2600............ 3...............2 days
IMS and SIP.................................................................................MB2300............ 3...............3 days
AAA Diameter...............................................................................QS1301............ 3...............2 days
UMTS and HSPA
UMTS System Overview..............................................................MB350.............. 2...............2 days
Cell Planning for UMTS Networks................................................MB2005............ 3...............2 days
Introduction to UMTS Optimization..............................................RP2400............ 3............... 3 days
HSPA Principles and Application..................................................RP2500............ 3...............1 day
UMTS Core Network....................................................................MB2004............ 3...............3 days
UMTS Air Interface.......................................................................MB2002............ 3...............3 days
GSM and GPRS
GSM System Overview................................................................MB20................ 2...............2 days
GSM-R Engineering Overview.....................................................MB2803............ 2...............2 days
Packet Engineering for Cellular Mobile Networks........................MB1201............ 2...............2 days
GSM Air Interface.........................................................................MB50................ 3...............3 days
Cell Planning for GSM Networks..................................................RP2602............ 3...............3 days
2G to 4G Indoor Coverage Planning............................................MB1304............ 3...............3 days
Introduction to GSM Optimization................................................MB80................ 3...............3 days
Enhanced Data Rates for Global Evolution (EDGE)....................MD2201............ 3...............3 hours
Professional Mobile Radio (PMR)
TETRA System Overview.............................................................TR1302............. 2...............2 days
dPMR...........................................................................................PR1301............ 2...............1 day
TETRA Air-Ground-Air..................................................................TR1204............. 3...............1 day
TETRA Security............................................................................TR1301............. 3...............1 day
DMR System Design....................................................................PR1302............ 3...............2 days
TETRA Air Interface.....................................................................MB2601............ 3...............2 days
TETRA System Design................................................................TR1202............. 3...............2 days
TETRA Direct Mode Operation....................................................TR1203............. 3...............1 day
Radio Engineering
Level 1 courses are developed
and presented in a style designed
to be easily understood by those
without a technical background. Key
characteristics, uses, trends and
issues relating to technical topics are
examined in a concise and interactive
way. These courses assume no prior
knowledge of the subject matter.
Level 2 Courses
Level 2 courses contain technical
material that is suitable for
engineering staff. Some will find that
these courses completely satisfy their
requirements, while for others they
will be an ideal introduction to more
specialized content. These courses
also provide semi-technical staff with
a deeper appreciation of technology
issues, and, although they assume
no prior knowledge of the subject
matter, they do require the ability to
grasp technical concepts.
Level 3 Courses
Level 3 courses have been
developed for engineering staff who
require detailed knowledge of a
specialist area of technology. These
courses assume some underlying
knowledge of the broader, related
topic areas on which the detailed
content is built, as well as general
engineering skills and
knowledge appropriate
to the course topic.
Introduction to Radio....................................................................RP1302............ 1...............1 day
Radio Principles...........................................................................RP1301............ 2...............3 days
Radio System Design...................................................................RP1303............ 2...............3 days
Principles of Radio Site Engineering............................................RP2100............ 2...............2 days
Microwave Link Planning.............................................................RP1201............ 3...............2 days
Essential Technologies
Telecoms Today and Tomorrow – Technology Workshop............WR2901........... 1...............1 day
Introduction to Telecoms..............................................................TY2600............. 2...............3 days
2G to 4G Mobile Technologies.....................................................MB1101............ 2...............2 days
Broadband Access Technologies.................................................TY2701............. 2...............1 day
Next Generation Transmission.....................................................TY2702............. 3...............3 days
SS7 Engineering..........................................................................QS2500............ 3...............3 days
Mobile Intelligent Networks (CAMEL)..........................................MB90................ 3...............2 days
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