E

I --(1 + k - sinot)-1. (8.3.4) I 1 -(sin ot +(-kr Vsin2 ot - . (8.3.5) R + r R + rj R + rj 1 V ' Figure 8.6. The carbon microphone with dc supply E and load resistance R. Figure 8.6. The carbon microphone with dc supply E and load resistance R. 1 ' - '.(R+T) s.n +1 (R )2-1 (R T)-2 , + ( 3.7) Because kr. (R + r.) is smaller than unity higher order terms can be ignored. If it is desirable to reduce second harmonic distortion, kr. (R + r.) can be reduced, but in doing so the amplitude of the...

The Cdma Cellular Telephone System

The code-division multiple access cellular telephone system was designed to improve the capacity of the system and enhance the security of the messages as well as prevent fraudulent access to cellular telephone services 14 . The projected improvement in spectrum efficiency was a very powerful economic incentive for the service providers. Since no new bandwidth was assigned to the CDMA cellular system, it had to coexist with AMPS. CDMA is a wideband system requiring 1.25 MHz in each of the two...

System Design

Composite Video Signal Frequency

Figure 6.3 shows the basic components of a television transmitter. A system of lenses focus the image onto a camera tube which collects and codes the information about the brightness and position of each element of the matrix forming the picture by scanning the matrix. A pulse generator supplies pulses to the camera to control the scanning process. The output from the camera goes to a video amplifier for amplification and the addition of extra pulses to be used at the receiver for decoding...

Info

The complete ten-subscriber telephone system. Figure 8.46. The Strowger switch showing horizontal and vertical banks as well as wipers. Reprinted with permission from B. E. Briley, Introduction to Telephone Switching, AT& T, Bell Labs, 1983. Figure 8.46. The Strowger switch showing horizontal and vertical banks as well as wipers. Reprinted with permission from B. E. Briley, Introduction to Telephone Switching, AT& T, Bell Labs, 1983. (3) Some electrical or mechanical...

Ro Zl Z1 Z3

The equivalent circuit of the generalized form of the oscillator. Ro represents the output resistance of the amplifier. Figure 2.11. The equivalent circuit of the generalized form of the oscillator. Ro represents the output resistance of the amplifier. Substituting for ZL as defined in Equation (2.4.16), Equation (2.4.19) becomes R0(Z + Z2 + Z3)+Z2 (Z1 + Z3) For simplicity, we may assume that the impedances are lossless hence Z1 jXi, Z2 jX2 and Z3 jX Then Equation (2.4.20) becomes...

Introduction

A radio signal can be generated by causing an electromagnetic disturbance and making suitable arrangements for this disturbance to be propagated in free space. The equipment normally used for creating the disturbance is the transmitter, and the transmitter antenna ensures the efficient propagation of the disturbance in free space. To detect the disturbance, one needs to capture some finite portion of the electromagnetic energy and convert it into a form which is meaningful to one of the human...

Other Digital Cellular Systems

USDC (United States Digital Cellular) This system was designed to increase the capacity of the cellular telephone service. In one AMPS channel, USDC supports three subscribers. USDC is a time-division multiple access (TDMA) system and it uses the same FDD for the downlink and uplink separated by 45 MHz. Like the system based on CDMA, conversion to USDC has to be carried out within the bandwidth reserved for cellular telephone services. It uses p 4 differential quadrature phase shift keying in a...

The Antenna

Antenna structures can take many physical forms, from the ''whip'' antenna used mostly for in-car radios, through ''rabbit ears'' for television to the microwave parabolic ''dish'' used in satellite communication. These are only the most common examples of antennas which are used for reception of broadcast signals. The antenna is the last processor of the signal at the transmitting end and the first at the receiving end. Antennae vary widely in shape, size and complexity, depending on the...

The Facsimile Machine

In 1843, the British Patent Office issued a patent with the title ''Automatic electrochemical recording telegraph'' to the Scottish inventor Alexander Bain (1810-1877). The essence of the invention is shown in Figure 1.2. Two identical pendulums are connected as shown by the telegraph line. For simplicity, we assume the ''message'' to be sent is the letter H and it is engraved on a metallic plate and shaped to the appropriate radius so that the ''read'' stylus makes contact with the raised...

Coaxial Cable

In a coaxial cable, one conductor is in the form of a tube with the second running concentrically along the axis. The inner conductor is supported by a solid dielectric or by discs of dielectric material placed at regular intervals along its length. A number of these cable are usually combined together with twisted pairs to form a multi-pair cable. The structure of the coaxial cable ensures that, at normal operating frequencies, the electromagnetic field generated by the current flowing in it...

Radio Circuit Design

In 1864, James Maxwell (1831-1879), a Scottish physicist, produced his theory of the electromagnetic field which predicted that electromagnetic waves can propagate in free space at a velocity equal to that of light 9 . Experimental confirmation of this theory had to wait until 1887 when Heinrich Hertz (1857-1894) constructed the first high-frequency oscillator. When a voltage was induced in an induction coil connected across a spark gap, a discharge would occur across the gap setting up a...

R

Circuit Designs Wireless World

Figure 8.39. a The zero-voltage comparator and its output characteristics. b The comparator for vj and vj and its output characteristics. Vz of the diode. Evidently the clamping voltages were chosen so that a 0 0.7 volts and Vz amp V 1 - the system voltage. The input-output characteristics are given in Figure 8.39 a . Now consider the circuit in Figure 8.39 b where there are two input voltages v and vi connected by equal resistances R to the inverting input of the operational amplifier....

L

Which gives a resonant frequency, f 10.001 x 106Hz - a change of less than 0.2 . The corresponding quality factor of the crystal is then Qo 130,000. Figure 2.18. a The equivalent circuit of the crystal and its package. b The electrical symbol for the crystal. Figure 2.18. a The equivalent circuit of the crystal and its package. b The electrical symbol for the crystal. Figure 2.19. The reactance characteristics of the crystal. Note that this is not to scale. Figure 2.19. The reactance...

Terrestrial Microwave Radio

Terrestrial microwave radio is a relatively inexpensive medium for long-haul telephone and television signals. Its assigned frequencies are 2, 4, 6, 11, and 18 GHz, which make the system a line-of-sight operation. The distance between repeater stations is approximately 40 km at the lowest frequency and 3 km at the highest frequency, where rain can cause severe attenuation. It is well suited to difficult terrain where the cost of burying or stringing up on posts any form of cable would be...

ClassC Amplifier

In a class-C amplifier, the current in the active device flows for a period much less than p radians of the output waveform. The active device current waveform is therefore highly non-sinusoidal. In a class-A or -B amplifier this would give a correspondingly non-sinusoidal output. However, in the class-C amplifier the collector load consists of a parallel LC circuit which is tuned to the frequency of the input signal. The tuned circuit sometimes referred to as a tank circuit presents a very...

Basic Telephone Equipment

Microphone Cross Section

The basic telephone has surprisingly very few parts. These are shown in Figure 8.1. When the microphone is connected in series with the battery, it produces a current proportional to the pressure of the sound impinging on it. The transformer eliminates the dc and sends the ac portion of the current through the line. The earphone at the receiving end changes the variation of the current into sound. Obviously, the system works in the reverse direction. Figure 8.5 shows a cross-section of the...

Diagonal Clipping

The electromagnetic disturbance created by the transmitter is propagated by the transmitter antenna and travels at the speed of light as described in Chapter 2. It is evident that, if the electromagnetic wave encounters a conductor, a current will be induced in the conductor. How much current is induced will depend on the strength of the electromagnetic field, the size and shape of the conductor and its orientation to the direction of propagation of the wave. The conductor will then capture...

A2 The Ideal Transformer

A transformer may be considered to be ideal if it satisfies all the conditions below 1 2 The primary inductance L11 and the secondary inductance L22 both approach infinity while the ratio L11 L22 remains finite. 3 The coupling coefficient k 1. 4 The windings have no resistance and the magnetic core has no losses. 5 Stray capacitances of the coils are zero and stray capacitance between the coils is zero. To investigate the impedance transformation property of the transformer, consider the...

Co

A typical intermediate-frequency television signal before and after detection. Figure 7.2. A typical intermediate-frequency television signal before and after detection. such pulses horizontal sync pulses only shown . The horizontal synchronization pulses are used to control the initiation of the horizontal sweep of the electron beam in the picture tube so that synchronism with the horizontal sweep of the electron beam in the camera tube is maintained. Similarly, the vertical...

Telecommunication Before The Electric Telegraph

The need to send information from one geographic location to another with the minimum of delay has been a quest as old as human history. Galloping horses, carrier pigeons and other animals have been recruited to speed up the rate of information delivery. The world's navies used semaphore for ship-to-ship as well as from ship-to-shore communication. This could be done only in clear daylight and over a distance of only a few kilometres. The preferred method for sending messages over land was the...

Digital Telephone

Until the introduction of the digital telephone all signals from the station set were transmitted to the central office in analog form over the subscriber loop, which in Inputs from 8-Stage Shift Register Figure 8.32. The switches in Figure 8.31 are replaced by FETs. most cases, is the twisted pair of plastic-insulated copper wire. In the central office it may be subjected to a number of sophisticated signal processing techniques, depending on the routing of the message and the medium of...

Amplitude Modulation Theory

Figue Modulation Wave

In order to simplify the derivation of the equation for an amplitude modulated wave, we make the simplification that the modulating signal is a sinusoid of angular frequency ms and that the carrier signal to be modulated also sinusoidal has an angular frequency oc. Let the instantaneous carrier current be The amplitude modulated carrier must have the form i A B sin ost sin oct 2.2.4 The waveform is shown in Figure 2.1. The current may then be expressed as i A kA sin ost sin oct 2.2.5 Figure...

Systems Design

The development of the modern fax machine starts with the adoption of the recommendations of the Consultative Committee of the International Telegraph and Telephones CCITT of the standards which came to be known as Group 3 G3 . Group 1 and 2 standards which incidentally were analog had been essentially ignored by the North American fax industry. The discussion of G3 standards started in 1976 during the General Assembly of the CCITT which had in the meantime transformed itself into the...

Squarelaw Modulator

From Equation 2.2.5 it can be seen that the modulated current has two components These suggest that the circuit required to achieve amplitude modulation must generate the product of the carrier and the modulating signal frequency and add to this a suitably scaled carrier signal. The multiplication can be approximated by a non-linear element, such as a diode, and the addition by connecting the two sources in series. Since the diode has a voltage-current characteristic which is approximately a...

Component Design

Antenna design is outside the scope of this book. However, a brief qualitative discussion can be found in Section 2.9. Further discussion of antennas for commercial FM reception is presented in Section 5.2.1. Frequencies for commercial FM 88-108 MHz occupy the spectrum between channels 6 and 7 of the VHF television frequencies 54-88 MHz and 174-216 MHz, respectively . Except for slight differences in the physical dimensions, the antennas tend to take the same form. These are frequency ranges in...

The Radiofrequency Amplifier

Class Amplifier

The choice of an amplifier to boost the power coming out of the modulator to the level required to drive the antenna can be made when the following points have been considered 1 The amplifier must be linear so as to preserve the nature of the modulated signal. 2 The output power of the amplifier can vary from a few watts to hundreds of kilowatts. 3 A high conversion efficiency is a necessity when high power is a requirement. The portion of the dc power supplied to the amplifier which is not...

Draw Pcm Signalling Structure For The Bell D1 24 Channel System

Flywheel Diodes Centre Tap

A combination of the series and shunt sampling gates improves performance. 9.3.2.5 Operational Amplifier Sampling Gate. The circuit is shown in Figure 9.12. The operational amplifier is connected to give a gain of R2 R1 when the transistor is in the off state. When the transistor is on, R2 is short-circuited and the gain is reduced to unity. 9.3.2.6 Multiplier Sampling Gate. A PAM sampler can be seen as a multiplication of the analog signal and a train of pulses. The process is...

Shortwave Radio

Frequencies between 3 MHz and 30 MHz are set aside for use in long distance radio communication. This frequency band is generally referred to as the short-wave band. The wavelength that lies between 1 m and 100 m is short compared to that of the medium wave. It was pointed out in Section 2.9 that the increased frequency of the carrier used in short-wave communication gives its electromagnetic transmission wave increasingly directional properties. Transmission antennae can be designed to...

Frequency Modulation Theory

Frequency Modulation Theory

While a saw-tooth modulating signal provides a simple picture of the FM signal, a sinusoidal modulating signal is the simplest for the derivation of the mathematical expressions to describe the FM signal. Figure 4.1. The sawtooth waveform vs frequency modulates a carrier to give the output vfm. Note that the relative change in frequency has been exaggerated for clarity. In normal FM radio, the change in frequency relative to the carrier is less than 0.15 Figure 4.1. The sawtooth waveform vs...

Problems

8.1 Describe the attractive features of the carbon microphone that make it well suited to the telephone system. A carbon microphone has a static resistance of 75 O and it is connected in series with a 12 V battery and a load resistor R. A sound wave impinging on the microphone causes a sinusoidal variation of the microphone resistance with a peak value equal to 15 of the static value. What is the value of the load resistor R if the second harmonic component of the current is 7.5 of the current...

Access Techniques

11.3.1 Multiplex and Demultiplex Revisited When modulation is used to accommodate a number of signals on a single channel we refer to it as multiplexing. Figure 11.2 shows five baseband signals, each of which occupies the frequency band 300 Hz to 3 kHz. By choosing suitable carrier frequencies for each one, they may be transmitted over the same cable or the airwaves by radio and subsequently demodulated with no interference between them. When different carrier frequencies are used to multiplex...

Quadrature Detector Circuit

Quadrature Detector Circuit

Figure 5.4. a The phasor diagram when signal frequency is lower than carrier frequency. b The phasor diagram when signal frequency is higher than carrier frequency. Figure 5.4. a The phasor diagram when signal frequency is lower than carrier frequency. b The phasor diagram when signal frequency is higher than carrier frequency. Replacing R2 in Equation 5.2.7 by Z2 gives It is evident that V1 and V2 are no longer at right angles to each other. The angle between them depends on the magnitude and...

E3 The Clocked Sr Flipflop

Repetition Error Gates

A flip-flop is normally a part of a much larger system of gates. Each gate takes a finite amount of time to change its state so there is no guarantee that the two inputs S and R of a flip-flop will arrive simultaneously or whether one will arrive before the other. For example, because of delays in their respective paths, suppose S 0 and R 1 and they are both supposed to change states simultaneously, then if S arrived a little ahead of R, we would momentarily have S 1 and R 1 an unacceptable...

E2 Basics Of Sr Flipflop Circuits

Flip Flop Circuit With Nand Gates

Figure E.1 a shows the NOT gate non-resettable equivalent of the flip-flop, b shows the resettable equivalent using NOR gates and c shows a second realization using NAND gates. In the flip-flop circuit shown in Figure E.1 b , the S and R terminals are the control inputs. Q and Q are the outputs and they are complementary that is when one of them is a 1 the other must be a 0 . There are four different combinations of 1s and 0s that can exist at the terminals S and R. 1a If we assume that S R 0...

Converting the ClassC Amplifier into a Frequency Multiplier

To convert a class-C amplifier into a frequency multiplier with a multiplication factor of 2, the L and C of the tank circuit are chosen to resonate at 2oo when the input signal frequency is fflo. Successful operation of the system demands that the Q factor Figure 2.22. The output waveform of a class-C amplifier after a single pulse excitation. Note the sinusoidal waveform and the exponential decay of the envelope. Figure 2.22. The output waveform of a class-C amplifier after a single pulse...

Stereophonic Fm Transmission

Composite Transmission Signal Picture

In an effort to create a realistic sound presentation from recorded music, two microphones are used, one to record the sound as it is perceived on the right side and the second on the left side. During playback the right- and left-hand side signals have to be fed to the right- and left-hand side loudspeakers, respectively. The listener sitting in front of the speakers can distinguish the sounds of the different instruments as coming from their proper positions when the music was recorded. When...

The Paging System

Paging System Block Diagram

There are a number of occupations in which the professional has to move around from one job to the next and essentially is almost never available at a wireline telephone. The paging system is designed to receive and store information until the professional is ready to read it. They are most commonly used by home appliance servicemen, office equipment servicemen, doctors, photographers, and in the last few years they have become very popular with teenagers. Different paging systems have varying...

Pulse Amplitude Modulation Circuit Diagram

Pulse Amplitude Modulation Circuit

Other larger groups can be formed, for example 6 mastergroups may be combined to form a jumbogroup with 3600 voice channels. To recover the original baseband signals from the various groups, the appropriate number of filtering demodulation processes will have to be carried out. At each stage of the demodulation process, the correct carrier will have to be reinstated for this to be possible. In FDM, voice signals were ''stacked'' in the frequency spectrum so that many such signals could be...

Design A Ce Circuit

Operating Point Transistor

When Equation 2.7.3 is plotted on the characteristics of the device shown in Figure 2.37 it gives a straight line with a slope equal to 1 Rc and intercepts on the y axis equal to Vcc Rc and on the x axis equal to Vcc. This line is known as the load line and determines the behavior of the device when it is connected to the collector load, Rc, and the supply voltage Vcc. Because the current in a class-A amplifier flows for the entire 2p radians of the input ac cycle, its analysis depends on a...

Generation Of Fm Block Diagram

Phase Shift Circuit

The use of a double-tuned circuit provides increased dynamic range and improves the linearity by balancing the non-linearity of one LC circuit with the other. Note that the push-pull arrangement shown here will generate predominantly odd harmonics. vfm t A sin oct mf sin ost cos oct 4.4.4 vfm t Afsin oc t 1 mf sin oc os t sin oc os t . 4.4.5 It should be noted that the above approximation eliminates all the sidebands except the two closest to the carrier. The modulation is then...

Frequency Multiplier

Hartley Oscillator Circuit

The purpose of the frequency multiplier is to raise the frequency generated by the crystal-controlled oscillator to the value required for the transmitter carrier. As explained earlier, it is not possible to obtain physically robust crystals at high Figure 2.20. a A Hartley oscillator with one of the inductors replaced by a crystal. This circuit is called a Pierce oscillator. The field-effect transistor may be replaced by any other suitable active device. b The equivalent circuit of the Pierce...

The Doted Pointsof The Transformer

Npn Transformers

The current flowing in each transistor is a half-sinusoid whose average value dc equivalent is c p. The average current for the two transistors is 2 c p. Since this current is flowing against a potential difference of Vcc, the dc power input is The complementary symmetry class-B amplifier has the following disadvantages 1 It requires two equal dc power supplies. 2 Complementary pairs of transistors are not easy to manufacture, especially at high power levels. 3 The circuit cannot have a voltage...