Radio Communication Jto Lice Study Material Sample

LICE-JTORadio Communication Systems 1 LICE-JTO Limited Internal Competitive Examination STUDY MATERIAL Radio Communication Systems Principles of Radio Communication, A.M., F.M. Radio, Phase Modulation. Signal conditioning and Transmission Study of special chips, output interfacing, output instruments-indicators, recorders, data acquisition systems data loggers, servo mechanism, electronic process control instrumentation. Wave propagation, Microwave devices & components, microwave measurements, antenna fundamental & their characteristic. Audio Engineering, sound transducers, sound recording & reproduction, sound transmission, radio transmission, radio reception. © 2016ENGINEERS INSTITUTE OF INDIA® .All Rights Reserved LICE / JTO / SSC : Classroom , POSTAL, All India TEST Series 28-B/7, Jia Sarai, Near IIT, HauzKhas, New Delhi-110016. Ph. 011-26514888. www.engineersinstitute.com Radio. A. 011-26514888. F.MEMORY 108-114 SYLLABUS: Radio Communication Systems Principles of Radio Communication. New Delhi-110016.engineersinstitute. Audio Engineering. servo mechanism.M. radio transmission.LICE-JTO Radio Communication Systems 2 CONTENTS Basics of Radio Communication 3. Ph. electronic process control instrumentation. microwave measurements. sound transmission. Signal conditioning and Transmission Study of special chips. radio reception. output interfacing. Near IIT. HauzKhas.6 Modulation 7-17 AM /FM Radio System 17-20 Microwave Engineering 20-63 ANTENNAS 63-75 Microwave measurements 76-86 Data acquisition system and data loggers 87-89 Audio Engineering 90-94 Sample Questions 94-107 IMPORTANT TERMS . Microwave devices & components. data acquisition systems data loggers.. All India TEST Series 28-B/7. Wave propagation. POSTAL.M. Jia Sarai. © 2016ENGINEERS INSTITUTE OF INDIA® .All Rights Reserved LICE / JTO / SSC : Classroom . Phase Modulation. www. sound recording & reproduction.com . recorders. antenna fundamental & their characteristic. sound transducers. output instruments-indicators. Remote sensing Wavelength Broadcasting TV. fixed and mobile satellite services 100 Broadcasting. Fixed satellite services. and distress frequencies. Meteor burst communication 1000 Fixed point to point communication. Remote sensing underground. Wireless LAN. radar systems. www. land services. Ph. New Delhi-110016. satellites. Satellite communication. Mobile services. sounds or intelligence of any nature by means of electromagnetic waves of frequencies lower than three thousand gigacycles per second (3000 GHz) propagated in space without artificial guide.LICE-JTO 3 Radio Communication Systems Basics of Radio Communication Radio or radio communication means any transmission. Navigation. Personal telephone systems.engineersinstitute. 3003000 Hz Frequency Long distance communication (fixed and marine). HauzKhas. or reception of signs. Examples of radio communication systems:       Radio broadcasting. amateur radio and broadcasting 3-30 kHz AM broadcasting. Broadcasting. Near IIT. FM. Mobile Cellular Telephony. images. Jia Sarai. radio beacons. signals. Maritime telegraphy Application The path loss © 2016ENGINEERS INSTITUTE OF INDIA® . All India TEST Series 28-B/7.All Rights Reserved LICE / JTO / SSC : Classroom .com . aeronautical and land. Mobile maritime aeronautical. Wireless microphones. TV broadcasting. Mobile services for maritime. writing. emission. Underwater Communication. 011-26514888. Navigation. Radio beacons Time and Frequency Normal. POSTAL. TV. navigation. Multimedia communication & Mobile Internet Classification of radio spectrum -10 km Term ELF VLF • 30-300 kHz 3003000 KHz 3-30 MHz 30-300 MHz 3003000 MHz 3-30 GHz 30-300 GHz 10 1000 100 10 100 10 10 -1 km -100 m -10 m -1 m -10 cm -1 cm -1 mm LF MF HF VHF UHF SHF EHF Radio Communication has three main problems: – Frequency assignments up 60 GHz -100 km Fixed services. military communication. • The key circuit is the mixer. Jia Sarai.LICE-JTO Radio Communication Systems – Noise – Sharing the radio spectrum 4 • In radio communication systems.  Bipolar and FETs can be used as RF amplifiers. which acts like a simple amplitude modulator to produce sum and difference frequencies. • The radio receiver best suited to this task is known as the super heterodyne receiver.  RF amplifiers provide some initial gain and selectivity and are sometimes called preselectors.  RF amplifiers minimize oscillator radiation.com . • The incoming signal is mixed with a local oscillator signal. 011-26514888. All India TEST Series 28-B/7. • Superheterodyne receivers convert all incoming signals to a lower frequency. also called a low-noise amplifier (LNA). the transmitted signal is very weak when it reaches the receiver. at which a single set of amplifiers is used to provide a fixed level of sensitivity and selectivity. • Gain and selectivity are obtained in the IF amplifiers. Block diagram of a superheterodyne receiver. Mixers and Local Oscillators  The output of the RF amplifier is applied to the input of the mixer. particularly when it has traveled over a long distance.  Tuned circuits help select the frequency range in which the signal resides. Ph. www. • Receivers must provide the sensitivity and selectivity that permit full recovery of the original signal. Near IIT. New Delhi-110016. RF Amplifier  The antenna picks up the weak radio signal and feeds it to the RF amplifier. known as the intermediate frequency (IF).All Rights Reserved LICE / JTO / SSC : Classroom . © 2016ENGINEERS INSTITUTE OF INDIA® . POSTAL.engineersinstitute. HauzKhas. • The signal has also picked up noise of various kinds. and the sum and difference frequencies of these signals. is rectified and filtered into a dc voltage by a circuit known as the automatic gain control (AGC) circuit. a quadrature detector (for FM).LICE-JTO Radio Communication Systems  The mixer also receives an input from a local oscillator or frequency synthesizer.  Since the intermediate frequency is usually lower than the input frequency. POSTAL. to control receiver gain. which recovers the original modulating information. or a product detector (for SSB). Ph. Automatic Gain Control  The amplitude of the RF signal at the antenna of a receiver can range from a fraction of a microvolt to thousands of microvolts. Demodulators  The highly amplified IF signal is finally applied to the demodulator. and most of the gain is obtained in these stages. HauzKhas. and sometimes the RF amplifier.  The recovered signal. receivers are designed with very high gain so that weak signals can be reliably received.  The demodulator may be a diode detector (for AM). New Delhi-110016. or intermediate frequency (IF). www.  Selective tuned circuits provide fixed selectivity. IF amplifiers are easier to design and good selectivity is easier to obtain.  The signal is amplified by one or more IF amplifier stages.com .  Typically. the amplitude of which is directly proportional to the amplitude of the received signal. Near IIT.  The mixer output is the input signal.  This dc voltage is fed back to the IF amplifiers. which is usually ac.  AGC circuits help maintain a constant output level over a wide range of RF input signal levels.engineersinstitute.All Rights Reserved LICE / JTO / SSC : Classroom . 011-26514888. © 2016ENGINEERS INSTITUTE OF INDIA® . All India TEST Series 28-B/7. Jia Sarai. the local oscillator signal. Automatic Gain Control  The output of a demodulator is usually the original modulating signal.  A tuned circuit at the output of the mixer selects the difference frequency. this wide signal range is known as the dynamic range. 5 IF Amplifiers  The output of the mixer is an IF signal containing the same modulation that appeared on the input RF signal.  The output of the demodulator is then usually fed to an audio amplifier.  The local oscillator is made tunable so that its frequency can be adjusted over a relatively wide range. Mixing Principles  Frequency conversion is a form of amplitude modulation carried out by a mixer circuit or converter. 6 Frequency conversion  Frequency conversion is the process of translating a modulated signal to a higher or lower frequency while retaining all the originally transmitted information.g.  The oscillator is the carrier. wireless comm. intermediate frequency. Jia Sarai. Ph. high-frequency signals are converted to a lower.  In satellite communications. interference from other wireless devices Frequency Carries/Channels  The information from sender to receiver is carrier over a well-defined frequency band. is influenced by physical obstructions. Advantages and disadvantages of wireless communication (Important for LICE)  Advantages:  mobility  a wireless communication network is a solution in areas where cables are impossible to install (e..  With AGC. and the signal to be translated is the modulating signal. New Delhi-110016.)  easier to maintain  Disadvantages:  has security vulnerabilities  high costs for setting the infrastructure  unlike wired comm. climatic conditions. Near IIT.LICE-JTO Radio Communication Systems  However. producing distortion and reducing intelligibility.  The function performed by the mixer is called heterodyning. the overall gain of the receiver is automatically adjusted depending on the input signal level. POSTAL. This is called down conversion.engineersinstitute.  The output contains not only the carrier signal but also sidebands formed when the local oscillator and input signal are mixed. HauzKhas. www.All Rights Reserved LICE / JTO / SSC : Classroom . This is called up conversion. long distances etc. All India TEST Series 28-B/7. hazardous areas. a mixer essentially performs a mathematical multiplication of its two input signals. and the sine wave from a local oscillator is applied to the other input. © 2016ENGINEERS INSTITUTE OF INDIA® . 011-26514888.  Like an amplitude modulator.  Mixers accept two inputs: The signal to be translated to another frequency is applied to one input.com .  In radio receivers. applying a very high-amplitude signal to a receiver causes the circuits to be overdriven. the original signal is generated at a lower frequency and then converted to a higher frequency. All Rights Reserved LICE / JTO / SSC : Classroom . Example      Assume a spectrum of 90KHz is allocated over a base frequency b for communication between stations A and B Assume each channel occupies 30KHz. New Delhi-110016. 011-26514888. HauzKhas. www.com 7 . Jia Sarai. Ph.engineersinstitute. There are 3 channels Each channel is simplex (Transmission occurs in one way) For full duplex communication:  Use two different channels (front and reverse channels)  Use time division in a channel Radio waves generation  when a high-frequency alternating current (AC) passes through a copper conductor it generates radio waves which are propagated into the air using an antenna  radio waves have frequencies between:  3 Hz – 300 KHz .LICE-JTO Radio Communication Systems  This is called a channel  Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate)  Different frequency bands (channels) can be used to transmit information in parallel and independently. Near IIT. POSTAL.000 miles per second  radio waves become weaker as they travel a long distance © 2016ENGINEERS INSTITUTE OF INDIA® .low frequency  300 KHz – 30 MHz – high frequency  30 MHz – 300 MHz – very high frequency  300 MHz – 300 GHz – ultra high frequency  radio waves are generated by an antenna and they propagate in all directions as a straight line  radio waves travel at a velocity of 186. All India TEST Series 28-B/7. POSTAL. HauzKhas.LICE-JTO Radio Communication Systems Modulation  Modulation = adding information (e. All India TEST Series 28-B/7. www. 011-26514888. New Delhi-110016. Ph. Near IIT.g.All Rights Reserved LICE / JTO / SSC : Classroom . Jia Sarai.engineersinstitute. voice) to a carrier electromagnetic (radio) signal Digital modulation techniques © 2016ENGINEERS INSTITUTE OF INDIA® .com 8 . Jia Sarai. New Delhi-110016.LICE-JTO Radio Communication Systems Frequency Modulation (FM) / Amplitude Modulation (AM) Radio frequency interference Radio signal attenuation (path loss) © 2016ENGINEERS INSTITUTE OF INDIA® . www. Near IIT.All Rights Reserved LICE / JTO / SSC : Classroom .engineersinstitute.com 9 . HauzKhas. All India TEST Series 28-B/7. POSTAL. Ph. 011-26514888. HauzKhas. • Significant power for whole range of frequencies. Video (0 .4 kHz). and aircraft communications.and high-frequency applications. coaxial cable and fiber optic cable. eg: Audio (0 . • The carrier signal is represented byc(t) = A cos(wct) • The modulating signal is represented bym(t) = B sin(wmt) • Then the final modulated signal is [1 + m(t)] c(t)= A [1 + m(t)] cos(wct)= A [1 + B sin(wmt)] cos(wct) © 2016ENGINEERS INSTITUTE OF INDIA® . This produces upper and lower sidebands.engineersinstitute. • Change the carrier signal characteristics (amplitude. www. Jia Sarai. • Carrier communication • Use technique of modulation to shift the frequency. Ph.6 MHz). which are the sum and difference frequencies of the carrier wave and modulating signal. New Delhi-110016. • Suitable for radio/microwave and satellite communication. POSTAL. Amplitude modulation is implemented by mixing the carrier wave in a nonlinear device with the modulating signal. CB radio. Main advantages of AM are small bandwidth and simple transmitter and receiver designs. • Transmit information bearing (message) or baseband signal (voice music) through a communication channel • Baseband = is a range of frequency signal to be transmitted. Near IIT.All Rights Reserved LICE / JTO / SSC : Classroom .LICE-JTO Radio Communication Systems 10 Amplitude Modulation • Amplitude Modulation is the simplest and earliest form of transmitters • AM applications include broadcasting in medium. 011-26514888. • Transmission through twisted pair cable. • Not suitable for radio/microwave and satellite communication. frequency and phase) following the modulating signal amplitude. All India TEST Series 28-B/7.com . • Communication channel: • Transmission without frequency shifting. • The instantaneous amplitude of a carrier wave is varied in accordance with the instantaneous amplitude of the modulating signal. Ph. over modulation is present Modulation Index for Multiple Modulating Frequencies Two or more sine waves of different. New Delhi-110016. All India TEST Series 28-B/7. Near IIT. Jia Sarai. POSTAL.All Rights Reserved LICE / JTO / SSC : Classroom .LICE-JTO Radio Communication Systems = A cos(wct) + A m/2 (cos((wc+wm)t)) + A m/2 (cos((wc-wm)t)) The information signal varies the instantaneous amplitude of the carrier AM Characteristics • AM is a nonlinear process • Sum and difference frequencies are created that carry the information.engineersinstitute. expressed by the equation: m= • Em Ec When the modulation index is greater than 1.com 11 . uncorrelated frequencies modulating a single carrier is calculated by the equation m  m12  m22     Bandwidth © 2016ENGINEERS INSTITUTE OF INDIA® . www. • Modulation Index . 011-26514888.The ratio between the amplitudes between the amplitudes of the modulating signal and carrier. HauzKhas. calculated thus: PEP  Vp 2 2 RL Frequency Modulation. the peak envelope power is used  The peak power envelope is simply the power at modulation peaks. but the most important power measurement is that of the portion that transmits the information  AM carriers remain unchanged with modulation and therefore are wasteful  Power in an AM transmitter is calculated according to the formula at the right  m2   Pt  Pc1  2   Quadrature AM and AM Stereo  Two carriers generated at the same frequency but 90º out of phase with each other allow transmission of two separate signals  This approach is known as Quadrature AM (QUAM or QAM)  Recovery of the two signals is accomplished by synchronous detection by two balanced modulators Suppressed-Carrier AM  Full-carrier AM is simple but not efficient  Removing the carrier before power amplification allows full transmitter power to be applied to the sidebands  Removing the carrier from a fully modulated AM systems results in a double-sideband suppressed-carrier transmission  Single-Sideband AM  The two sidebands of an AM signal are mirror images of one another  As a result. and many other forms of vehicle. New Delhi-110016.engineersinstitute.LICE-JTO Radio Communication Systems 12  Signal bandwidth is an important characteristic of any modulation scheme  In general. All India TEST Series 28-B/7. a 3dB improvement in signal-to-noise ratio is achieved as a result of SSBSC Power in Suppressed-Carrier Signals  Carrier power is useless as a measure of power in a DSBSC or SSBSC signal  Instead. being used in taxis. 011-26514888.com . Jia Sarai. Ph.All Rights Reserved LICE / JTO / SSC : Classroom . www. one of the sidebands is redundant  Using single-sideband suppressed-carrier transmission results in reduced bandwidth and therefore twice as many signals may be transmitted in the same spectrum allotment  Typically. HauzKhas. and FM is also used for a variety of forms of two way radio communications. © 2016ENGINEERS INSTITUTE OF INDIA® . a narrow bandwidth is desirable  Bandwidth is calculated by: B  2Fm Power Relationships  Power in a transmitter is important. FM is widely used for a variety of radio communications applications. Near IIT. FM broadcasts on the VHF bands still provide exceptionally high quality audio. and it is especially useful for mobile radio communications. POSTAL. Similarly when the information reaches a minimum the carrier will be at its lowest frequency below the nominal carrier frequency value. then no deviation of the carrier will occur. When the information voltage reaches its maximum value then the change in frequency of the carrier will have also reached its maximum deviation above the nominal value.LICE-JTO Radio Communication Systems 13 In Frequency Modulation (FM) the instantaneous value of the information signal controls the frequency of the carrier wave. New Delhi-110016.com . Near IIT.All Rights Reserved LICE / JTO / SSC : Classroom . The frequency fi of the information signal controls the rate at which the carrier frequency increases and decreases. The maximum change in frequency that can occur to the carrier from its base value fc is called the frequency deviation. When the information signal is zero. the frequency of the carrier decreases. HauzKhas. Notice that as the amplitude of the information signal increases above 0 volts. This is illustrated in the following diagrams. The amplitude of the carrier remains constant throughout this process.engineersinstitute. Jia Sarai. POSTAL. 011-26514888. fi must be less than fc.e. As with AM. The dynamic range is the ratio of the largest and smallest analogue information signals that can be transmitted. Ph. www. and is given the symbol fc. Modulation Index © 2016ENGINEERS INSTITUTE OF INDIA® . voltage range) of the transmission. the frequency of the carrier increases. All India TEST Series 28-B/7. This sets the dynamic range (i. and as the amplitude of the information signal decreases below 0 volts. The effect of this is that a much greater proportion of the transmitted power is in the sidebands (rather than in the carrier). HauzKhas.engineersinstitute. fi . regardless of the information signal or modulation index. and the information baseband is the high fidelity range 20Hz to 15kHz. (As a general rule. An FM transmission is a constant power wave. to the maximum information frequency. is chosen to be 75kHz. Thus the modulation index. Jia Sarai.  is 5 and such broadcast requires an FM signal bandwidth given by: BandwidthFM Radio  2(f c  f i (max) )  2(75  15)  180kHz Points to remember. . As its name suggests the bandwidth is much larger than AM.  fc .) Determination of Bandwidth for FM Radio FM radio uses a modulation index. New Delhi-110016. as shown below:  f c fi Theoretically.LICE-JTO Radio Communication Systems 14 All FM transmissions are governed by a modulation index. an FM spectrum has an infinite number of sidebands. The modulation index. All India TEST Series 28-B/7. > 1. which is more efficient than AM. and this is called wideband FM. POSTAL. In national radio broadcasts using FM. www. spaced at multiples of fi above and below the carrier frequencyfc . However the size and significance of these sidebands is very dependent on the modulation index. the relative amplitude of the carrier component decreases and may become much smaller than the amplitudes of the individual sidebands. 011-26514888. which controls the dynamic range of the information being carried in the transmission. because it is operated at a constant amplitude with symmetrical changes in frequency. Near IIT.All Rights Reserved LICE / JTO / SSC : Classroom . the frequency deviation of the carrier fc . any sidebands below 1% of the carrier can be ignored. Ph. . . is the ratio of the frequency deviation. Signal Conditioning © 2016ENGINEERS INSTITUTE OF INDIA® .com . . As  increases. LICE-JTO Radio Communication Systems 15 PC-based Data Acquisition System  In the last few years. analyze. accurate and affordable. control. HauzKhas. PC-baseddata acquisition and control systems are widely used in industrial andlaboratory applications like monitoring. All India TEST Series 28-B/7. Near IIT. data acquisition andautomated testing. store.com . www. New Delhi-110016.  Transducers and actuators  Signal conditioning  Data acquisition and control hardware  Computer systems software A data acquisition system consists of many components that are integrated to:  Sense physical variables (use of transducers)  Condition the electrical signal to make it readable by an A/D board  Convert the signal into a digital format acceptable by a computer  Process. 011-26514888. Jia Sarai.All Rights Reserved LICE / JTO / SSC : Classroom . and display the acquired data with the help of software © 2016ENGINEERS INSTITUTE OF INDIA® .  Selecting and building a DA&C (Data Acquisition and Control) systemthat actually does what you want it to do requires some knowledge ofelectrical and computer engineering. POSTAL. industrial PC I/O interface products have becomeincreasingly reliable.engineersinstitute. Ph. POSTAL. radio is used for the transmission of sounds (voice and music) and pictures (television). that is. Jia Sarai. Near IIT. All India TEST Series 28-B/7. they process sounds into continuously varying patterns of electrical signals which resemble sound waves. amplified. • A radio wave acts as a carrier of information-bearing signals. New Delhi-110016. The modulated carrier is also amplified. Such waves radiate at the speed of light and are transmitted not only by line of sight but also by deflection from the ionosphere. that is. • Digital radio uses a transmission system in which the signals propagate as discrete voltage pulses. which is the older method of broadcasting. • In its most common form. • The two most common types of modulation used in radio are amplitude modulation (AM) and frequency modulation (FM). 011-26514888. Both AM and FM are analog transmission systems.com . www. rather than in the carrier wave itself. the information may be encoded directly on the wave by periodically interrupting its transmission (as in dotand-dash telegraphy) or impressed on it by a process called modulation. before transmission. an analog audio signal is converted into a digital signal. or frequencies added to the carrier wave.engineersinstitute. as patterns of numbers. • The actual information in a modulated signal is contained in its sidebands. A digital radio broadcast offers compact-disc-quality reception and reproduction on the FM band and FM-quality reception and reproduction on the AM band. and then applied to an antenna that converts the electrical signals to electromagnetic waves for radiation into space. which may be transmitted in the AM or FM frequency range. and used to modulate a carrier wave that has been generated by an oscillator circuit in a transmitter. a transmitter and receiver are employed. Frequency modulation minimizes noise and provides greater fidelity than amplitude modulation. © 2016ENGINEERS INSTITUTE OF INDIA® .LICE-JTO Radio Communication Systems 16 Radio Transmission and Reception • For the propagation and interception of radio waves. HauzKhas.All Rights Reserved LICE / JTO / SSC : Classroom . The sounds and images are converted into electrical signals by a microphone (sounds) or video camera (images). Ph. New Delhi-110016.All Rights Reserved LICE / JTO / SSC : Classroom . HauzKhas. Jia Sarai. POSTAL.engineersinstitute. www. 011-26514888.LICE-JTO Radio Communication Systems SAMPLE FILE To Buy complete package Call +91-9990657855. Near IIT. All India TEST Series 28-B/7. Ph. 011-26514888 © 2016ENGINEERS INSTITUTE OF INDIA® .com 17 .