COMMUNICATION ELECTRONICS BY FRENZEL 3RD EDITION PDF
Book Communication Electronics 3rd Ed- Frenzel - Free ebook download as PDF File .pdf) or read book online for free. The communication electronics by frenzel 3rd edition free download book builds on the previous communication electronics by frenzel free ebook download. Principles of. Electronic. Communication Systems. Louis E. Frenzel Jr. Fourth Edition . This new fourth edition of Principles of Electronic Communication Systems is fully revised and updated to .. Third-generation digital cell phones.
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COMMUNICATION. ELECTRONICS. Principles and Applications. HA. Third Edition. Frenzel. Basic Skills in Electricity and Electronics. TATA MCGRAW-HILL. COMMUNICATIONS ELECTRONICS by Frenzel CHAPTER 1: Introduction to .. The average output of an SSB transmitter is one-fourth to one-third of the PEP. time Communication Electronics By Frenzel 3rd Edition PDF is available at our online library. With our complete resources, you could find Communication.
Modems are needed to convert digital signals to analog signals and vice versa to make them compatible with the standard voice-grade telephone system.
Modems are used with any computer that must communicate with another computer over long distances using the telephone system. A scrambler ensures that long strings of binary 0s or 1s are broken up into replacement codes with few successive 0 or 1 bits.
Balanced modulator. A carrier recovery circuit, usually a phase-locked loop. Differential BPSK. XNOR gate and a 1-bit delay flip-flop. Shift register. AM and PSK. Trellis code modulation is a form of QAM, used at data rates of bps or above, that incorporates a coding scheme that makes error detection and correction faster and easier.
It is used because at faster data rates over the telephone system the bit error rate is much higher than at rates less than bps. The process of modifying an intelligence signal in such a way that its spectrum is spread over a wide frequency range rather than being confined to a narrow singlechannel bandwidth.
Frequency-hopping and direct-sequence SS. A frequency synthesizer. A pseudorandom sequence generator.
Random background noise. The identifying characteristic of a spread spectrum signal is the unique pseudorandom code being used. Dwell time. A shift register with XOR feedback or a specially programmed microcomputer. The PSN signal is a unique binary code sequence used for each station operating over a shared spectrum.
It allows one station to be distinguished from another. Synchronizing the receiver to the desired signal. Data security and resistance to jamming or interference from other signals. Cellular telephone, satellite, and radar. Voice signals are converted to serial digital data before they are sent to the SS equipment. Code division multiple access CDMA.
Redundancy, special codes, encoding methods, parity, block-check character, cyclical redundancy check. Repeat the transmission until it is correctly received. Reed Solomon. Bit error rate BER. Parity bit. Block-check code, or BCC. The corresponding bits in each word are added without carry to form the blockcheck character. Vertical redundancy check. XOR gate. Longitudinal redundancy check. A block of data is treated as if it were one very large binary number.
It is divided by a smaller binary number called the generating function. The resulting quotient is abandoned, and the remainder is retained. The remainder is the CRC. A shift register with feedback through XOR gates. A CRC is generated at the receiver using the received data block.
It is then compared to the received CRC. If the two match, the data is correct. The sum is zero , indicating no errors in a bit position. Trellis, Viterbi, turbo recursive codes. The last field in a protocol frame is usually a block check sequence or CRC for error detection. A CRC word. Interoperability refers to the ability of one type of equipment to operate compatibly and communicate with the equipment of another manufacturer. Use protocols based on the OSI layers.
Applications, presentation, session, transport, network, data link, physical. Physical, data link, network, and applications. A temperature sensor such as a thermistor or resistive temperature device RTD monitors the temperature. This signal is serialized and packaged into a protocol packet by a microprocessor. It is then sent to modulate a low-power radio transmitter with antenna. The receiving antenna picks up the signal and recovers the original digital signal, which is then put back into parallel form and sent to an interface on the computer.
A program in the computer reads the data from the interface and stores it in memory. The program takes the data word and processes it so that it is displayed as the correct temperature on the video screen of the computer. Cellular telephone. Many phones could share a common band simultaneously. The conversations would be secure and private. Remote controls for TV sets, garage doors, and car doors, radio-controlled airplanes or cars—all via AC power lines. Spread spectrum and OFDM are spectrally efficient because the disperse the very high data rate signals over a broad spectrum that is typically less spectrum than other methods use for the same data rate.
B Chapter 12 Answers to Questions 1. To permit individual PCs to communicate, share peripherals, and exchange software. The MAN is smaller. A cable TV network or a large company. About users per LAN. Star, ring, bus. Ring and bus. The telephone system is a WAN. The fiber optic backbones of the Internet are WANs. Fiber optic cable. A SAN is a storage area network, a system made up of a redundant array of independent disks RAID or just a bunch of disks JBOD forming a storage facility for company or organization that can be accessed by servers and users via a high speed network.
Wireless is the normal medium used in a PAN. The main advantage of a mesh network is its reliability because of one node in the network is disabled or out of range an alternate path can be formed or taken to ensure communications.
Coaxial cable is self-shielding and thus less subject to noise pickup. AWG 22, 24, Network interface card. A transceiver or repeater. This reduces the load on the bus and collisions, thereby greatly improving transmission speed. A hub is a centralized connection point for attaching individual PCs to the network bus.
PoE means power over Ethernet. This is a variation of the Ethernet standard that permits DC power to be distributed over the twisted pair cable that carries the high speed data. Star in the newer systems. It is used because clock recovery is easy. Twisted pair and fiber optic cable. Ethernet nodes complete contend for the bus. If one node transmits, no others can transmit until the first transmission is complete.
If two stations try to transmit at the same time, a collision occurs and both stations stop sending. They wait a random time and start The one waiting the shorter time captures the bus first. Layers 1 and 2. Maximum range fiber optic cable 1 Gbps: 10km 10 Gbps: 40 km distance depends on the wavelength of the laser transmitters, shorter wavelengths and nm for the shorter distances and longer wavelength nm for the longer distances.
Backbones connecting large LANs or small metro area networks. Makes clock recovery easier and permits implementation of error detection and correction. Passive optical networks PON. Unshielded twisted pair UTP. A back plane is a printed circuit board that interconnects connectors into which other boards are plugged.
A router is an example. Four parallel lanes of 10 Gbps paths are combined to produce 40 Gbps. Ten 10 Gbps lanes are combined to produce a Gbps path. The line rate of a high speed path is different from the actual raw data rate because of the extra overhead bits of forward error correction codes added for reliability.
Carrier Ethernet software. A data center is a facility with multiple servers, switches, and routers that form networks and facilitate network communications. Factory automation, in which multiple computers controlling robots, machine tools, computer vision systems, and other equipment are usually networked.
Number of nodes on the network, the amount of traffic or activity on the LAN, and the access method used. It takes longer to transmit the two extra bits and that slows the over transmission. Yes, a single fiber can support 40 Gbps or Gbps over shorter distances using NRZ or over longer distances using multiplexing or modulation methods. B Chapter 13 Answers to Questions 1. Coaxial cable and open wire line.
Coaxial cable is more widely used. Twin lead. PL, SO N-type connector. F connector. LC low-pass filter. Surge impedance. Velocity factor is the ratio of the speed of a signal in a transmission line to the speed of light radio waves in free space.
Since the speed of a signal in a transmission line is less than that in free space, the electrical wavelength of a transmission line is less than a wavelength or fraction thereof in free space. Figure 7 B The cutoff frequency decreases with length.
Constant value of voltage and current. All the power transmitted down the line from the generator is not absorbed by the load; therefore, some of the unabsorbed power is reflected back up the line toward the generator.
The transmitted power at the antenna is less than that applied to the transmission line by the transmitter because of cable attenuation as well as the loss of power due to reflection of power. Open and shorted at the end. Resonant line. Length does not affect SWR. Use an open quarter-wave or shorted half-wave line. They act as an inductive or capacitive reactance. One wavelength. Figure 8 Answers to Problems 1. Open or shorted. See Fig. A single point at the center of the chart. An open quarter wave or shorted half-wavelength line acts like a series tuned or resonant LC circuit.
A short quarter-wave or open half-wave line acts like a parallel resonant LC circuit. Upper UHF and microwave. Microstrip is a copper line on the insulating surface of a dielectric backed up by a ground plane on the other side of the insulating surface.
If the input strays outside, the lock range, the PLL will go out of lock and the VCO will operate at its free-running frequency. The capture range of a PLL is that narrow band of frequencies over which a PLL will recognize and lock onto an input signal.
The capture range is narrower than the lock range and it makes the PLL look like a bandpass filter. The PLL is the best frequency demodulator because its filtering action removes noise and interference and its highly linear output faithfully reproduces the original modulating signal.
Increasing the reverse bias on a voltage variable capacitor causes its capacitance to a. Increase b. Decrease 2. Decrease 3. In the circuit of Fig. Decrease page Frenzel 4. A crystal is operating in its series resonant mode.
A VVC is connected in series with it. The crystal frequency a. Increases b. Decreases 5. Which is capable of greater frequency deviation? LC oscillator b. Crystal oscillator 6. A reactance modulator is set up to act like an inductive reactance. If the modulating signal increases in amplitude, the effective inductance decreases. This causes. Voltage-variable capacitors should not be forward-biased. For highly stable carrier generators, LC oscillators are preferred over crystal oscillators.
A reactance modulator is used with crystal oscillators. Phase modulation produces frequency variation as well as amplitude variation of the carrier. In the circuits of Fig. In the phase modulator of Fig. Should the input frequency increase or decrease for the average voltage output of the low-pass filter in a pulse-averaging discriminator to increase?
The Foster-Seeley discriminator is sensitive to input amplitude as well as frequency variations. The ratio detector requires a limiter. The lock range of a PLL is narrower than the capture range. VXO R04 C1, C2, L1 VCO FM input A radio transmitter generates the carrier signal, provides power amplification, and applies modulation. The simplest transmitter is an oscillator that is keyed off and on to produce cw Morse code.
Most transmitters consist of a crystal oscillator used to generate an accurate and stable carrier frequency, a buffer amplifier that isolates the carrier oscillator from its load, one or more driver amplifiers to increase the RF power level.
The final stage is modulated. Frequency modulation transmitters use class C amplifiers to increase the RF power level.
Single-sideband transmitters generate the carrier and modulation at a low frequency and then translate it up with a mixer, Linear amplifiers are used to increase the power level. In a class A amplifier, collector current flows continuously, The output is directly proportional to the input; therefore, it is a linear amplifier. Class B amplifiers are usually connected in a push-pull circuit where one transistor amplifies each half of the input signal Class C amplifiers are biased beyond cutoff.
Collector current pulses in a class C amplifier are converted into a continuous sine wave by a resonant circuit. The collector current pulses in a class C amplifier contain many harmonics which are filtered out by the tuned output circuit.
A class C amplifier can be used as a frequency multiplier by connecting a resonant circuit tuned to some integer multiple of the input frequency in the output. RF amplifiers may oscillate because of feedback from internal transistor capacitance.
This can be eliminated, or prevented, by neutralization, a process that cancels the feedback with out-of-phase feedback. Frequency multipliers can be cascaded to produce higher output frequencies. In an FM transmitter, the frequency multipliers increase the deviation as well as the carrier frequency. Impedance-matching networks are used to interconnect RF amplifiers and to couple power to the antenna to ensure the optimum transfer of power.
The pi and T networks are preferred since Q can be controlled. Maximum power transfer occurs when the load impedance equals the generator source impedance.
Radio-frequency transformers are typically constructed with doughnut-shaped powdered-iron cores called toroids. The impedance-matching ability of a transformer is determined by its turns ratio: Inductors made with toroids for a given inductance are smaller, use fewer turns of wire, have a higher Q, and do not require shielding.
A balun is a transformer connected in a special way to transform circuits from balanced to unbalanced or vice versa and to provide impedance matching. Toroid transformers and baluns are broadband devices that operate over a wide bandwidth.
Broadband, linear, untuned RF power amplifiers provide amplification over a broad frequency range. Speech-processing circuits in a transmitter prevent overmodulation, prevent excessive signal bandwidth, and increase the average transmitted power in AM and SSB systems. A voice clipper uses diodes to limit the amplitude of the audio modulating signal. A low-pass filter smoothes out any clipping distortion and prevents excessive sidebands.
Voice compressors use automatic-gain control AGC circuits to limit the audio amplitude. The gain of the circuit is inversely proportional to the audio signal amplitude. In AGC circuits, a rectifier and filter convert the audio or RF into a dc voltage that controls the gain of an audio or RF amplifier to prevent overmodulation. The gain of a transistor amplifier can be varied by changing the collector current.
A Class A Transistor amplifier has an efficiency of 50 percent. The output power is 27W. Elimination of self-oscillation can be accomplished with either a feedback inductor or a capacitor. With no input, a class B amplifier does not conduct. Frequency multipliers with factors of 2, 3, 4, and 5 are cascaded. The input is 1. A class C amplifier has a de supply voltage of 28 V and an average collector current of 1.
List the two popular types of three element LC matching networks. Most impedance-matching networks are made adjustable tunable. Assume a Q of A transformer has 6 turns on the primary and 18 turns on the secondary.
An RF transformer with a 1: Name the two primary purposes of speech processing. Name the two main purposes of a low-pass filter in a speech-processing circuit. In an audio compressor, do low-level signals receive more or less amplification?
Speech processing may be done on the RF signal or the audio signal. AM, SSB A, B, AB L network The simplest form of communications receiver is the tuned radio-frequency TRF receiver which provides RF and AF gain, selectivity, and a demodulator.
The two primary characteristics of a receiver are selectivity and sensitivity. Selectivity is the ability to separate signals on different frequencies. Sharper selectivity with steeper response curve skirts can be obtained by cascading tuned circuits.
The shape factor of a response curve is the ratio of the 6O-dB-down bandwidth to the 6-dB-down bandwidth. The lower the shape factor, the better the selectivity.
Sensitivity is the ability of the receiver to pick up weak signals and is a function of gain. The disadvantages of a TRF receiver are tuning difficulties and selectivity varying with frequency. These problems of a TRF receiver are eliminated by using a superheterodyne superhet receiver. A superhet uses a mixer to translate the incoming signal to a lower frequency, known as the intermediate frequency IF , where fixed gain and selectivity. Most of the gain and selectivity in a superhet is obtained in the IF amplifier.
Low IFs are preferred because higher selectivity and better stability can be obtained with simple circuits.
Low IFs usually cause image interference problems.
Communication Electronics by Frenzel 3rd Edition Pdf
An image is a signal on a frequency separated from the desired signal frequency by 2 times the IF value that interferes with reception. The mixer will convert both the desired signal and the image to the IF. Image interference is caused by poor receiver input selectivity that does not adequately reject the image. Image interference can be reduced by using a double-conversion superhet that uses two mixers and IFs. The first IF is high to eliminate images, and the second is low to ensure good selectivity.
The most critical part of any receiver is the front end which consists of the RF amplifier and mixer as these circuits add the most noise to a weak signal.
Noise is any random interference to a weak signal. A measure of a receiver's noise performance is its signal-to-noise SIN ratio. External noise comes from industrial, atmospheric', and space sources. Industrial noise sources are ignitions, motors and generators, switching devices, and fluorescent lights. Atmospheric noise comes from lightning and other sources. Space noise comes from the sun as well as other stars and extraterrestrial sources.
Internal noise from electronic components also interferes with reception and can totally mask weak signals. Most internal noise comes from thermal agitation-the random movement of electrons and atoms in a material due to heat. Other types of internal noise are shot and transit-time noise in semiconductors. Noise cannot be eliminated, but its effect can be minimized. Noise performance of a receiver or circuit is expressed in terms of the noise figure F, also called the noise factor, which is the ratio of the SIN input to the SIN output.
It is usually given in decibels. Thermal noise is random and is often referred to as white noise or Johnson noise. Since noise is a mixture of all random frequencies, its level can be reduced by narrowing the bandwidth.
Most receivers get their selectivity from double-tuned LC circuits. Most receivers have AGC circuits so that a wide dynamic range of input signal amplitude scan be accommodated without distortion.
The gain of a bipolar transistor can be varied by changing its collector current. A squelch circuit is used to cut off the audio output to prevent annoying noise until a signal is received. Either the audio signal or background noise can be used to operate the squelch circuit. Continuous tone control squelch CTCS circuits permit selective signaling by allowing only low- frequency tones to trigger the squelch.
A beat frequency oscillator BFO is used in SSB and CW receivers to provide a carrier that will mix with the input signal in the demodulator to generate the audio output. A transceiver is a piece of communications equipment that combines a receiver and a transmitter in a common package where they share a common housing and power supply. Single-sideband transceivers allow sharing of the filter, LO stages, and other circuits.
Many new transceivers contain a frequency synthesizer that eliminates multiple crystal oscillators and LC tuned oscillators in the transmitter and receiver. A frequency synthesizer is a signal generator usually implemented with a PLL that produces LO and transmitter carrier signals in a transceiver.
A frequency synthesizer has the stability of a crystal oscillator, but the frequency can be varied in small, equal increments over a wide range. The frequency increments in a synthesizer are set by the frequency of the reference input to the phase detector.
The frequency of a synthesizer is changed by varying the divide ratio of the frequency divider between the VCO output and phase detector input. Phase-locked loop synthesizers often incorporate mixers and multipliers to permit more than one frequency to be generated. A tuned circuit can provide voltage gain. A tuned circuit has a Q of at its resonant frequency of kHz.
A parallel LC tuned circuit has a coil of 3 H and a capacitance of 75 pF. A tuned circuit has a resonant frequency of 10 MHz and a bandwidth of kHz. A filter has a 6-dB bandwidth of Hz and a dB bandwidth of Hz. For best selectivity and stability, the IF should be a. High b. Medium c. Low A superhet has an input signal of 15 MHz.
The LO is tuned to A desired signal at 27 MHz is mixed with an LO frequency of The LO may be above or below the signal frequency. List three sources of external noise. List three main types of internal noise. List four sources of industrial noise. Two types of. The noise at the output of a receiver will be less than the noise at the input.
The receiver amplifies noise as well as the signal. The noise figure of an amplifier is 2. An amplifier with a noise temperature of K is better than one with a rating of K.
An IF amplifier that clips the positive and negative peaks. A circuit that blocks the audio until a signal is received is called a n circuit. What components or circuits in Fig. If there was no audio output from the speaker but you knew that a signal was present, what two controls would you check first? What component provides most of the gain in this receiver?
Is the squelch signal or noise derived? Does this receiver contain a BFO? Where would you inject an audio signal to test the complete audio section of this receiver? What frequency signal would you use to test the IF section of this receiver, and where would you connect it? What component would be inoperable if C31 became shorted? Explain how you would connect a digital counter to this receiver so that it would read the frequency of the signal to which it was tuned.
A frequency synthesizer has a phase detector input reference of 10 kHz. The divide ratio is What three frequencies does the synthesizer in a transceiver usually generate? IF amplifier Image Intermediate frequency RF amplifier, mixer IF SSB, CW As the pot arm voltage goes more positive, the reverse bias across D1 increases, thus decreasing its capacitance and the overall capacitance of D1 in series with C14; this in turn increases the local oscillator frequency.
The squelch is signal derived The gain increases. U2, the MC IC, would lose supply voltage at pin 2. A digital counter could be connected to monitor the local oscillator output signal at pin 6 or 7 of the NE mixer IC. This would read the local oscillator frequency, which is Therefore, the counter would have to be preset to a value that is In this way, the IF value would effectively be subtracted from the input count to read the correct frequency.
Assume that the counter is set up to count four digits, The counter is preset to The counter counts Multiplexing is the process of transmitting multiple signals over a single communications channel.
The primary benefit of multiplexing is economic since multiple communications can take place for the cost of a single link plus the multiplexing equipment.
The two major types of multiplexing are frequency division and time division multiplexing. In frequency division multiplexing FDM , multiple signals share the common bandwidth of a single communications channel, each occupying a separate portion of the bandwidth.
In FDM, each signal modulates a subcarrier on a different frequency. The subcarriers are then linearly mixed to form a composite signal that is usually used to modulate a final carrier for transmission. A subcarrier oscillator is a VCO whose frequency varies linearly in proportion to the amplitude of a modulating dc or ac signal. Recovering the individual signals at the receiver is done with a demultiplexer whose main components are bandpass filters tuned to the individual subcarrier frequencies.
The telephone system routinely uses FDM systems to allow many conversations to be carried on a single cable. Single-sideband suppressed-carrier modulation is used in telephone FDM systems to minimize bandwidth requirements. In some FM broadcast systems, music is broadcast on a separate kHz subcarrier which is frequency modulated. In time division multiplexing TDM , each channel is assigned a time slot and may transmit for a brief period using the entire bandwidth of the medium.
Signal sources take turns transmitting. Both digital and analog signals may be transmitted by TDM. Analog signals are transmitted by converting them into a series of pulses whose amplitudes approximate the shape of the analog signal. This process is called pulse amplitude modulation PAM. Pulse-amplitude modulation is produced by sampling the analog signal. This is done by periodically opening a gate for a brief period, allowing a narrow portion of the analog signal to pass through.
Samples must be taken fast enough in order for high-frequency components to be recognized and adequately represented. A minimum sampling rate is 2 times the highest frequency component or upper bandwidth limit of the analog signal. This is called the sampling theorem.
Pulse-amplitude modulation signals may be multiplexed by allowing samples of several signals to be interleaved into adjacent time slots. Field-Effect transistor switches are commonly used in sampling gates and PAM multiplexers. They are controlled by digital circuits that set the sampling intervals and pulse rates.
The period of time during which each channel in a PAM system is sampled once is called a frame. Demultiplexing PAM signals requires some means of synchronization to ensure matching clock frequencies and channel timing at the receiver.
Special clock recovery circuits use the PAM signal itself to derive the clock signal at the receiver rather than generating it independently. This ensures perfect frequency and phase relationships.
A special sync pulse with a unique shape to distinguish it from the PAM pulses is used to keep the demultiplexer in synchronization with the multiplexer. The sync pulse usually occurs as the last pulse in a frame. In a multichannel PCM system, each signal is furnished with an analog-to-digital converter ADC and parallel-to-serial converter. The resulting binary outputs are digitally multiplexed using TOM techniques. Voice, telemetry data, video, and other analog signals may be transmitted via PCM.
Pulse-code modulation is generated by periodically sampling the analog signal as in PAM systems. Then the varying amplitude pulses are converted into proportional binary words by an ADC. This process is called quantizing. Quantizing means dividing a given signal voltage range into a number of discrete increments each represented by a binary code. Each analog sample is matched to the nearest binary level. Most ADCs have an 8-bit word providing a quantizing resolution of 1 in Most PCM systems, especially for voice transmission, use companding to compress the voice signal dynamic range by emphasizing lower-level signals and de-emphasizing higher-level signals.
Companding minimizes quantization error and improves noise immunity. Companding may be done by analog or digital techniques. Analog companders use diode circuits in amplifiers for compression and expansion. A T-1 system multiplexes 24 voice channels, each represented by an 8-bit word.
The sampling interval is s. A frame consists of twenty-four 8-bit words and a single sync pulse. The frame data rate is 1. The sampling rate of a codec is usually 8 kHz. Pulse-code modulation is preferred over PAM because of its superior noise immunity.
Which statement is most correct? Multiplexing uses multiple channels to transmit multiple signals. Multiplexing uses multiple channels to transmit individual signals. Multiplexing uses a single channel to transmit multiple signals. Multiplexing uses a single channel to transmit a single signal. PLL SSB FM AID converter T-1 A transmission line is a two-wire cable used to carry RF energy between two different pieces of communications equipment or between an antenna and a receiver or transmitter.
The two most common types of transmission lines are balanced and coaxial. The characteristic impedance of a balanced line is determined by its physical dimensions. The characteristic impedance of coax also depends on its physical dimensions.
The proper use of a transmission line is to terminate it in a load impedance equal to its surge impedance.
All the power applied to the line will be absorbed by the load. Wavelength is the distance between adjacent peaks of a RF wave. It is also the distance traveled by a signal in one cycle.
If a transmission line is not terminated in its characteristic impedance, the load will not absorb all the power. Some of it will be reflected back toward the generator. If the load on a transmission line is an open or short, all the power applied to the line will be reflected back to the generator.
The forward or incident power applied to the line combines with the reflected power to produce a pattern of voltage and current variations along the line known as standing waves. If the load impedance matches the line impedance, there are no standing waves. A measure of the mismatch between line and load impedances or the maximum and minimum voltage and current variations along, the line is the standing-wave, ratio SWR which is a number always greater than 1.
The SWR indicates how much power is delivered to the load and lost in the line. Every effort is made to reduce the SWR by using impedance-matching circuits to ensure that maximum power is delivered to the load. Transmission lines, one-quarter or one-half wavelength long and either shorted or open, act like resonant or reactive circuits. At UHF and microwave frequencies where one-half wavelength this less than 1 ft, transmission lines are commonly used to replace conventional LC tuned circuits.
A shorted quarter wave and an open half wave act like a parallel resonant circuit. Both an open quarter-wave circuit and a shorted half-wave circuit act like a series resonant circuit. The velocity of propagation of a radio signal is slower in a transmission line than in free space.
This difference is expressed as the velocity factor F for different types of lines. Coax has a velocity factor of 0.
The velocity factor of open wire line or twin lead is in the 0. An antenna or aerial is one or more conductors used to transmit or receive radio signals. A radio signal is electromagnetic energy made up of electric and magnetic fields at right angles to one another and to the direction of signal propagation.
The polarization of a radio signal is defined as the orientation of the electric field with respect to the earth and is either vertical or horizontal.
The most common antenna is the half wave dipole or doublet that has a characteristic impedance of approximately 73 flat the center. The dipole has a bidirectional figure-eight radiation pattern and is usually mounted horizontally but may also be used vertically.
A popular variation of the dipole is the folded dipole which is one-half wavelength long and has an impedance of Another popular antenna is the quarter-wave vertical. The earth acts as the other quarter wave to simulate a half-wave vertical dipole.
The quarter-wave vertical is referred to as a ground plane antenna. It is fed with coax with the center conductor connected to the antenna and the shield connected to earth ground, to an array of quarter- wave, wires m called radials, or to a large, flat, metal surface.
The characteristic impedance of a ground plane is about It has an omni directional radiation pattern that sends or receives equally well in all directions. A directional antenna is one that transmits or receives over a narrow range in only one direction.
Directional antennas made up of two or more elements focus the radiation into a narrow beam, thus giving the antenna gain.
The gain of the, antenna is the power amplification resulting from the concentration of power in one direction. The gain may be expressed as a power ratio or in decibels. The effective radiated power ERP of an antenna is the power input multiplied by the antenna power gain. Directional antennas with two or more elements are caIled arrays. There are two types of arrays: Parasitic elements called reflectors and directors when spaced parallel to a half wave dipole driven element help focus the signal into a narrow beam.
The measure of the directivity of an antenna is the beam width or beam angle measured in degrees. Driven arrays consist of two or more half wavelength elements, each receiving power from the transmission line. The three most popular driven arrays are the collinear, end-fire, and broadside.
A widely used driven array is the log periodic antenna which exhibits gain, directivity, and a wide operating frequency range. A radio wave propagates through space in one of three ways: The ground or surface wave leaves the antenna and follows the curvature of the earth. The ground wave is only effective on frequencies below 3 MHz. The skywave propagates from the antenna upward where it is bent back to earth by the ionosphere. The ionosphere is a portion of the earth's atmosphere 30 to mi above the.
The ionosphere is made up of three layers of different ionization density: The F layer is the most highly ionized and causes refraction or bending of radio waves back to earth. The refraction of the ionosphere causes a radio signal to be bent back to earth with little or no attenuation long distances from the transmitter.
This is known as a skip or hop. Multiple skips or hops between the ionosphere and earth permit very long distances, even worldwide, communications. This effect is useful over the 3- to MHz range. At frequencies above 30 MHz, propagation is primarily by the direct or space wave which travels in a straight line between transmitting and receiving antennas.
This is known as line-of-sight communications. Radio waves ate easily blocked or reflected by large objects. The communications distance at VHF, UHF, and microwave frequencies is limited to the line-of-sight distance between transmitting and receiving antennas. The line-of-sight distance D is limited by the curvature of the earth and is dependent upon the heights h, and h, of the transmitting and receiving antennas, respectively. To extend transmission distances at VHF, UHF, and microwave frequencies, relay stations known as repeater stations receive and retransmit signals.
A line 4 in. A coax line has a shield braid with an inside diameter of 0. A coax bas a antenna load. The maximum voltage along a transmission line is V, and the minimum voltage is 90V. The reflection coefficient of a transmission line is 0. A transmission line bas an SWR of 1. The power applied to the line, is 90 W. The following lines look like a series resonant circuit: An open transmission line 6 in.
A coax bas a velocity factor of 0. A radio wave has its magnetic field horizontal to the earth. List two basic types of antenna arrays. List three kinds of driven arrays.
Yagis and driven arrays may be operated either horizontally or vertically. A quarter-wavelength of coax with a velocity factor of 0.
List the three paths that a radio signal may take through space. Radio waves are easily reflected by large objects.
The ionosphere reflects radio waves. Q section, matching stub Microwaves are radio signals in the frequency range from I to GHz. The RF spectrum below UHF is mostly already fully occupied leaving little or no room for the growth of new radio services. At microwave frequencies, tremendous bandwidth is available for new radio services as well as for wide-bandwidth signals such as TV, multiplexed signals, or computer data.
The microwave frequencies are used primarily for telephone communications, radar, and satellite communications. Other microwave applications include cable TV, space communications, radio astronomy, and heating. The primary benefit of microwaves is wide bandwidth availability. The main disadvantages of microwaves are that they are limited to line-of-sight transmission distances, conventional components are not usable, and circuits are more difficult to analyze and design.
Balanced transmission line is not used for microwaves because of radiation losses. Coaxial cable is not used because of its high attenuation. The preferred transmission line for microwaves is waveguides. Because of the short physical length of transmission lines at microwave frequencies, quarter- and half- wave lines are commonly used for tuned circuits and filters. Two printed circuit board implementations of transmission lines, called stripline and microstrip, are widely used to create resonant circuits and filters.
A waveguide is a hollow metal pipe with a circular or rectangular cross section used for carrying microwave signals from one place to another. A waveguide acts like a high-pass filter, passing all frequencies above its cut-of frequency and rejecting those below it. The cutoff frequency fco of a waveguide depends upon its physical size. The microwave signal carried by a waveguide is made up of electric E and magnetic H fields that bounce off the walls of the waveguide as they propagate along its length.
The modes of a waveguide describe the various patterns of electric and magnetic fields that are possible. A transverse electric TE mode is one where the electric field is transverse or perpendicular to the direction of propagation. A transverse magnetic TM mode is one where the magnetic field is perpendicular to the direction of propagation. Half-wavelength sections of waveguides with shorted or closed ends are known as resonant cavities since they "ring" or oscillate at the frequency determined by their dimensions.
Cavity resonators are metallic chambers of various shapes and sizes that are used as parallel-tuned circuits and filters. They have a Q of up to 30, Point-contact and Schottky or hot-carrier diodes are widely uses as mixers in microwave equipment as they have low capacitance and inductance. Varactor diodes are widely used as microwave frequency multipliers.
Multiplication factors of 2 and 3 are common with power levels up to 20 Wand efficiencies up to 80 percent. Step-recovery or snap-off diodes are also widely used as frequency multipliers with multiplication factors up to 10, power ratings up to 50 W. A Gunn diode is a microwave semiconductor device used to generate microwave energy. When combined with a microstrip, stripline or resonant cavity, simple low power oscillators with frequencies up to 50 GHz are easily implemented.
Both are used in microwave oscillators. A klystron is a vacuum tube used for microwave amplification and oscillation. Klystrons use a cavity resonat or to velocity modulate an electron beam which imparts energy to another cavity, producing power amplification.
Klystrons are available which produce from a few to many thousands of watts. A single-cavity reflex klystron is used as a microwave oscillator. Klystrons are being gradually replaced by Gunn diodes and traveling-wave tubes. A magnetron is a diode vacuum tube used as a microwave oscillator in radar and microwave ovens to produce powers up to the megawatt range. In a magnetron, a strong magnetic field creates circular paths of electron flow to excite cavities into oscillation.
A traveling-wave tube TW T is a microwave power amplifier with very wide bandwidth. A microwave signal applied to a helix around the TW T produces velocity and density modulation of the electron beam over a long distance which induces a higher-power signal in the helix.
The most commonly used microwave antenna is the horn, which is essentially a rectangular waveguide with a flared end. A pyramidal horn flares in both waveguide dimensions.
Communication Electronics by Frenzel 3rd Edition Pdf
A sectoral horn flares in only one dimension. A parabolic or dish-shaped reflector is used with most microwave antennas to focus the RF energy into a narrow beam and increase gain. The parabolic reflector usually has a diameter that is no less than 10 wavelengths at the operating frequency.
The gain and directivity of a parabolic reflector antenna is directly proportional to its diameter. Parabolic reflector antennas are fed by placing a horn antenna at the focal point or by placing the horn at the center of the reflector and placing a small reflector at the focal point. The latter is known as Cassegrain feed.
A helical antenna is made up of six to eight turns of heavy wire or tubing to form a coil or helix. It is fed with coax and is backed up with a reflector. Helical antennas produce circular polarization where the electric and magnetic fields rotate. The polarization may be right-hand or left-hand depending upon the direction in which the helix is wound.
Helical antennas can receive either vertically or horizontally polarized signals but can only receive a circularly polarized signal of the same direction. A popular omnidirectional microwave antenna is the bicone. List seven reasons why microwaves are more difficult to work with than lower frequency signals. List four popular uses for microwaves. Name four techniques that have helped squeeze more signals into the given spectrum.
The TV channels 2 to 13 occupy a total bandwidth of about 72 MHz. Twin lead is not used at microwave frequencies.
A rectangular waveguide has a width of 1. A waveguide has a cutoff frequency of 5 GHz. It will pass a signal of 8 GHz. It will pass a signal of 3 GHz.
List three reasons why conventional diodes and transistors do not work in the microwave region. Klystrons can be used as amplifiers or oscillators. A magnetron operates as an amplifier. A horn antenna is six wavelengths long at 8 GHz. The width of a horn antenna is 8 cm. The height is 6 cm. The operating frequency is 8 GHz. A parabolic reflector antenna has a diameter of 9 m. The frequency of operation is 8 GHz. A helical antenna will receive either vertical or horizontally polarized signals.
Federal Communications Commission 7. LCR H, E TEO,1 P-type silicon, tungsten whisker Schottky barrier, or hot carrier Gunn Gunn diodes, TWTs Cassegrain A satellite is a physical object that orbits a celestial body. A communications satellite containing electronic equipment acts as a repeater or relay station between two earth stations. The basic component of a communications satellite is a receiver-transmitter combination called a transponder.
A satellite stays in orbit because the gravitational pull of the earth, is balanced by the' centripetal force of the revolving satellite. Satellite orbits about the earth are either circular or elliptical.
A satellite that orbits directly over the equator 22, mi from earth is said to be in a geostationary orbit. It revolves in synchronism with the earth's rotation, so it appears to be stationary when seen from points on the earth. A satellite is stabilized in orbit by spinning it on its axis or building in spinning flywheels for each major axis roll, pitch, yaw. Attitude adjustments on a satellite are made by firing small jet thrusters to change the satellite's position or speed.
The location of a satellite is determined with latitude and longitude measurements that designate a point on the earth subsatellite point SSP directly below the satellite. Azimuth and elevation angles determine where to point an earth station so that it intercepts the satellite.
Satellites are launched into orbit by rockets that give them vertical as well as forward motion. A geosynchronous satellite is initially put into an elliptical orbit where its apogee is 22, mi high.
The apogee kick motor is then fired to put the satellite into its final circular geostationary orbit. Many satellites are put into orbit by launching them from NASA's space shuttle. Most satellites operate in the microwave region. Microwave satellites operate on assigned frequency bands designated by a letter. Common communications satellite bands are the C 3. Satellite bands are typically MHz wide and are divided into 12 segments, each 36 MHz wide. A transponder is used to cover each segment.
Frequency reuse is a technique that allows two sets of transponders to operate on the same frequency, thus doubling channel capacity.
The two sets of channels use antennas of different polarizations to prevent interference with one another. Spatial isolation is another technique for frequency sharing. It uses highly directional spot-beam antennas to prevent interference between stations on the same frequency. The main subsystems in a satellite are the communications; power; telemetry, tracking; and control TIC ; propulsion; attitude stabilization; and antenna subsystems.
A transponder consists of a low-noise amplifier LNA that receives and amplifies the up-link signal, a mixer that converts the signal to another lower frequency, and a high-power amplifier that retransmits the signal on its new down-link frequency. Double-conversion transponders use two, mixers, one to translate the up-link signal to an IF where it is amplified and filtered, and another to translate the signal to its final down-link frequency.
Regenerative transponders demodulate the up-link signal to recover the baseband signals and then use them to remodulate a downlink transmitter. This improves the SIN ratio. In a broadband transponder, a single mixer converts all channels within the MHz bandwidth simultaneously to their downlink frequencies. These are selected by channel bandpass filters and then amplified by individual power amplifiers. In a channelized transponder, each channel has its own LNA, bandpass filters, mixer, and high-power amplifier.
The power subsystem consists of solar panels, batteries, dc-to-dc converters, and regulators. The solar panels convert sunlight into de power to operate all satellite electronics and to charge the batteries that take over when sunlight is blocked. The TTC subsystem contains a receiver that picks up commands from a ground station and translates them into control signals that initiate some action on board. The telemetry system monitors physical conditions within the satellites and converts them into electrical signals that are transmitted back to earth.
The propulsion system consists of the apogee kick motor that puts the satellite into final orbit and the jet thrusters that are used for positioning and attitude control. The stabilization subsystem for attitude control consists of spin components or three-axis flywheel gyros. The antenna system consists of one or more highly directional horn or parabolic antennas and an omnidirectional TTC antenna. The transmit subsystem takes the baseband voice, video, or computer data signals: An up converter translates the signal to its final up-link frequency before it is amplified and transmitted.
Transistor power amplifiers are used in low-power earth stations; klystrons are used in high-power narrowband stations; and TWTs are used in high-power broadband stations. Earth stations feature large- parabolic dish antennas with high gain and directivity for receiving the weak satellite signal.
The receive subsystem in an earth station amplifies the signal with an LNA and then separates the channels with bandpass filters. Down conveners translate the signals to a lower IF where they are demodulated and demultiplexed. The GCE in an earth station interfaces the baseband signals to the transmit and receive subsystems. The receive GCE performs demodulation and demultiplexing.
The transmit GCE performs modulation and multiplexing. The most common application for satellites is communications. Another major use of satellites is surveillance and reconnaissance. Film cameras, TV cameras, infrared sensors, and radars are all used to observe a variety of conditions on earth from surveillance satellites. Satellites playa major role in military and defense systems not only for communications but also for surveillance. The satellite Global Positioning System GPS makes accurate navigation possible anywhere on earth with a low-cost microwave receiver.
A satellite is kept in orbit by a balance between two forces: Name two ways satellites are stabilized in space. List the three main functions of a transponder. List the three main types of power amplifiers used in earth stations. All earth stations contain telemetry, control, and instrumentation subsystems.
Name four types of surveillance sensors. What are the name and the purpose of the satellite system developed by the military? Name three uses for surveillance satellites.
TWT Data communications is the transmission and reception of binary data between computers and other digital equipment. The earliest form of electronic communications, the telegraph, was a type of data communications. Turning a carrier off and on in a code of dots and dashes is a kind of data communications known as continuous wave CW. Teletype is a form of telegraph that uses the 5-bit Baudot code to transmit between typewriters like units. The two main methods of data transmission are serial and parallel.
In serial transmission, each bit is transmitted sequentially. In parallel transmission, all bits are transmitted simultaneously. Serial transfers are slower than parallel transfers but require only a single line or channel. Parallel transfers require multiple channels of lines called a bus.
Baud rate is the number of symbol changes per second. A symbol is an amplitude, frequency, or phase change. The channel-or bit-rate capacity of a channel is directly proportional to the channel bandwidth and the time of transmission.
The, bit rate is higher than the baud symbol rate if multiple-level symbol encoding is used. The two methods of data transmission are asynchronous and synchronous. In asynchronous transmission, data is sent one character at a time with start and stop bits. In synchronous transmission, data is sent as a continuous block of multiple characters framed with synchronization characters.
Synchronous transmission is faster than asynchronous transmission. In data communications, a binary 1 is referred to as a mark and a binary 0 as a space. Signals, whether voice, video, or binary, transmitted directly over a cable are known as baseband signals. Voice and video signals are analog but may be converted to digital for data communications transmission.
Signals that involve a modulated carrier a called broadband signals. Communications of binary data signal over the telephone network which is designed for analog signals is made possible by using a modem.
A modem is a modulator-demodulator unit that converts digital signals to analog and vice versa. Frequency-shift keying uses two frequencies for binary 0 and 1 and Hz or and kHz. It operates at speeds of baud or less. Binary PSK is generated by a balanced modulator. Binary PSK is demodulated by a balanced modulator. To properly demodulate BPSK, the carrier at the demodulator must have exactly the same phase as the transmitting carrier.The gain of a bipolar transistor can be varied by changing its collector current.
The ratio of the number of bit errors that occur for a given number of bits transmitted is known as the bit error rate BER. Helical antennas can receive either vertically or horizontally polarized signals but can only receive a circularly polarized signal of the same direction. A, B, AB A helical antenna will receive either vertical or horizontally polarized signals.
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