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Communication Electronics, 2nd ed. - Louis Frenzel [Answer Key/Solution Manual] - Download as PDF File .pdf), Text File .txt) or read online. Frenzel 2nd . Electronic-Communication_pdf. Uploaded by. buscandoconocerte · Communication Electronics, 2nd ed. - Louis Frenzel [Answer Key/Solution Manual]. Principles of electronic communication systems / Louis E. Frenzel Frenzel, Louis E · View online · Borrow · Buy . 5 editions of this work. Find a specific edition.

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Principles of electronic communication systems / Louis E. Frenzel Jr. —Fourth edition. pages cm. Includes index. ISBN (alk. paper) — ISBN . COMMUNICATIONS ELECTRONICS by Frenzel CHAPTER 1: Introduction to Electronic Communications CHAPTER 2: Amplitude Modulation and. Frenzel 2nd Edition Answer Key for All Chapters. Communication Electronics, 2nd ed. - Louis Frenzel [Answer Key/Solution Manual] .. Electronics 2nd comunication electronics 2nd by frenzel pdf communication.

Half Duplex b. Full Duplex c. Simplex The original electrical information signal to be transmitted is called the The process of modifying a high- frequency carrier with the information to be transmitted is called the The process of transmitting two or more information signals simultaneously over the same channel is called Continuous voice or video signals are referred to as being a.

Baseband b. Analog c. Digital d. Continuous waves Recovering information from a carrier is known as Subscribe to view the full document. Transmission of graphical information over the telephone network is accomplished by Measuring physical conditions at some remote location and transmitting this data for analysis is the process of Receiving electromagnetic emissions from stars is called a. The deviation ratio is the maximum frequency deviation divided by the maximum modulating frequency.

The modulation index determines the number of significant pairs of sidebands in an FM signal. The amplitudes of the carrier and sidebands vary with the modulation index and can be calculated with a mathematical procedure known as the Bessel functions.

The carrier or sideband amplitudes are zero at some modulation indexes. The bandwidth of an FM signal is proportional to the modulation index. There are two ways to calculate the bandwidth of an FM signal.

For FM, the percentage of modulation is the ratio of the actual frequency deviation and the maximum allowed frequency deviation multiplied by The primary advantage of FM over AM is its immunity to noise. Noise is short-duration amplitude variations caused by lightning, motors, auto ignitions, power transients, and other sources.

Limiter circuits in FM receivers clip off noise signals. Another benefit of FM over AM is the capture effect that allows the strongest signal on a frequency to dominate without interference from the other signal. A third benefit of FM over AM is greater transmitter efficiency since class C amplifiers may be used.

Communication Electronics

A major disadvantage of FM is that its bandwidth is wider than the bandwidth of AM. The spectrum space taken up by an FM signal may be limited by carefully controlling the deviation ratio. Another disadvantage of FM is that the circuits to produce and demodulate it are usually more complex and expensive than AM circuits. Noise occurs primarily at high frequencies; therefore, noise interferes more with high modulating frequencies. Interference from high-frequency noise can be minimized by boosting the amplitude of high-frequency modulating signals prior to modulation.

This is called pre-emphasis. Pre-emphasis is accomplished by passing the modulating signal through an RC network that linearly boosts the amplitude of frequencies above Hz in proportion to frequency. This increases the signal-to-noise ratio at the higher frequencies.

The effect of pre-emphasis is corrected for, in an FM receiver by de-emphasizing the higher frequencies by passing them through an RC low-pass filter. The pre-emphasis and de-emphasis networks have a time constant of 75 s and a cutoff frequency of Hz.

In FM, the carrier amplitude remains constant with modulation. As the modulating signal amplitude goes negative, the carrier frequency 6. When the modulating signal amplitude crosses zero, the phase shift and frequency deviation in a phase modulator are a.

At a maximum b. At a minimum c. Zero A phase modulator may use a low-pass filter to offset the effect of increasing carrier frequency deviation for increasing modulating a.

Amplitude b. Phase shift An FM signal produces more sidebands than an AM signal. The maximum frequency deviation of an FM signal is 10 kHz. The maximum modulating frequency is 3. An FM signal has a modulation index of 2. How many significant pairs of sidebands are produced? See Fig. In an FM signal that modulating frequency is a 1. The carrier frequency is kHz. Refer to Fig. What is the relative amplitude of the fourth significant pair of sidebands in an FM signal with a deviation ratio of 4?

A PM signal has a deviation ratio of 3. The maximum modulating signal is 5 kHz. If the maximum allowed deviation is 5 kHz but the actual deviation is 3. A negative sign on the carrier and sideband amplitudes in Fig. The carrier in an FM signal can never drop to zero amplitude.

Calculate the bandwidth of an PM signal with a maximum deviation of 10 kHz and a maximum modulating signal frequency of 4 kHz. Use the two methods given in the text, significant sidebands, and Carson's role, and compare your answers.

Explain the difference. Noise is primarily a variation in a. FM receivers reject noise because of built-in circuits. The in an FM receiver causes a stronger signal to dominate a weaker signal on the same frequency. An AM circuit is usually more complex and expensive than an FM circuit. Bessel functions A VVC is a specially designed silicon junction diode optimized for large capacitive variations. A reverse-biased junction diode will act as a small capacitor where the depletion region is the dielectric.

The capacitance of a varactor is inversely proportional to the reverse-biased voltage amplitude. The most common frequency modulators use a varactor to vary the frequency of an LC circuit or crystal in accordance with the modulating signal.

A reactance modulator is an amplifier that is made to appear inductive or capacitive by phase shift. It is used to produce wide deviation direct FM. Crystal oscillators are preferred for their frequency stability over LC oscillators, but only very small frequency deviation is possible with crystal oscillators. In a phase modulator, the carrier is shifted in phase in accordance with the modulating signal.

This produces indirect FM. One of the best phase modulators is a parallel tuned circuit controlled by a varactor. Most phase modulators produce very small amounts of frequency deviation. Frequency deviation and carrier frequency can be increased by passing them through a frequency multiplier. One of the oldest and best frequency demodulators is the Foster-Seeley discriminator that is a phase detector whose output voltage increases or decreases with phase changes produced by input frequency deviation.

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A Foster-Seeley discriminator is sensitive to input amplitude variations and, therefore, must be preceded by a limiter. A variation of the Foster-Seeley discriminator is the ratio detector widely used in older TV receiver designs. A primary advantage of the ratio detector is that no limiter is needed. A pulse-averaging discriminator converts an FM signal into a square wave of identical frequency variation using a zero crossing detector, comparator, or limiter circuit.

This circuit triggers a one shot that produces pulses that are averaged in a lowpass filter to reproduce the original modulating signal. The phase detector produces a different pulse width for different phase shifts. These pulse width variations are averaged in a low-pass filter to recover the modulating signal.

Quadrature detectors are available in IC form and are one of the most widely used TV audio demodulators. A differential peak detector is an IC FM demodulator that uses a differential amplifier and capacitive storage peak detectors plus tuned circuits to translate frequency variations into voltage variations.

A phase-locked loop PLL is a feedback control circuit made up of a phase detector, voltage controlled oscillator VCO , and low-pass filter. Input frequency changes cause a phase or frequency shift which, in turn, produces an error signal that forces the VCO to track the input and reduce their difference to zero.

The range of frequencies over which a PLL will track an input is called the lock range. 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. 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.

Communication Electronics

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.

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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.

Which of the following is not a source of noise? One way communication is called 9. Simultaneous two way communication is called a.

Half Duplex b. Full Duplex c. Simplex The original electrical information signal to be transmitted is called the The process of modifying a high- frequency carrier with the information to be transmitted is called the The process of transmitting two or more information signals simultaneously over the same channel is called Continuous voice or video signals are referred to as being a.

Baseband b. Analog c. Digital d. Continuous waves Recovering information from a carrier is known as. Introduction to Electronic Communications Transmission of graphical information over the telephone network is accomplished by Measuring physical conditions at some remote location and transmitting this data for analysis is the process of Receiving electromagnetic emissions from stars is called a.The range of frequencies over which a PLL will track an input is called the lock range.

Amplitude modulation can be produced by feeding the carrier to a voltage divider or other network and then varying one of the resistive elements in accordance with the modulating signal.

Inductors made with toroids for a given inductance are smaller, use fewer turns of wire, have a higher Q, and do not require shielding.

Spread spectrum offers the benefits of privacy or security of communications, immunity to jamming, and lower sensitivity to frequency-selective fading. Baseband refers to transmitting the information signal directly on the medium.

IF amplifier Amplitude modulation AM is the oldest and simplest form of modulation. Cassegrain External noise comes from industrial, atmospheric', and space sources.

Analog c.