Frenzel Communications Electronics Summary Chapter 3

CHAPTER 3

Amplitude Modulation Circuits
 

1.        Amplitude modulation can be accomplished by multiplying the carrier sine wave by a gain or attenuation factor that varies in accordance with the intelligence signal.

2.        Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. A diode is an example.

3.        The simplest AM circuit uses resistors to linearly mix the carrier and information signal, a diode to rectify the result, and a tuned circuit to complete the waveform.

4.        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. Common variable resistive components are diodes and FETs. PIN diodes are used at UHF and microwave frequencies.

5.        Low-level modulation is the process of generating 'the AM signal at low voltage and/or power levels and then using linear amplifiers to increase the power level.

6.        High-level modulation is the processes of amplitude modulating the final power amplifier of a transmitter.

7.        High-level modulation is accomplished with a collector (plate in vacuum tubes) modulator that varies the collector supply voltage in accordance with the modulating signal.

8.        For 100 percent high-level modulation, the modulation amplifier must produce an out put wave whose peak-to-peak is 2 times the collector supply voltage.

9.        For 100 percent high-level modulation, the modulation amplifier must generate an output power that is one-half of the final RF power amplifier input power (Pi =Vcc x Ic).

10.     The simplest and best amplitude demodulator is the diode detector. The AM signal is rectified by a diode and then filtered by a capacitor to recover the envelope which is the original modulating information.

11.     Balanced modulators are AM circuits that cancel or suppress the carrier but generate a DSB output signal that contains the upper (sum) and lower (difference) sideband frequencies.

12.     A popular balanced modulator is the lattice modulator that uses a diode bridge circuit as a switch. The carrier turns the diodes off and on letting segments of the modulating signal through to produce a DSB output signal. A carrier suppression of 40 dB is possible.

13.     Another widely used balanced, modulator is an integrated circuit (IC) using differential amplifiers as switches to switch the modulating signal at the carrier frequency. A popular device is the 1496 or 1596. Carrier suppression can be as high as 50 to 65 dB.

14.     The most common way of generating an SSE signal is to use the filter method which incorporates a balanced modulator followed by a highly selective filter that passes either the upper or lower sideband.

15.     To make both sidebands available, SSB generators use two filters, one for each sideband, or switch the carrier frequency to put the desired sideband into the fixed filter, bandpass.

16.     Most SSB, filters are made with quartz crystals.

17.     A quartz crystal is a frequency-determining component that acts like an LC circuit with a very high Q.

18.     Crystals have series and parallel resonant modes. These can be combined into a lattice (bridge) circuit that provides extremely sharp selectivity over a desired bandwidth.

19.     Ceramic filters use ceramic resonators that act like crystals but are smaller and lower in cost.

20.     Mechanical bandpass filters are also used in SSE generators. These devices use multiple resonant disks that vibrate at some frequency in the 200- to 500-kHz range.

21.     The phasing method of SSE generation uses two balanced modulators and 90° phase shifters for the carrier and modulating signal to produce two DSB signals that when added cause one sideband to be canceled out.

22.     In phasing-type SSE generators, the accuracy of the phase shifters determines the degrees of unwanted sideband suppression.

23.     Precision RC networks are normally used to produce the desired 90° phase shifts.

24.     A demodulator for SSE is a mixer such as a balanced modulator that, is called a product detector. The carrier is reinserted in the receiver with a local oscillator.

25.     Frequency translation or conversion is an AM process that converts a signal with any modulation to a higher (up conversion) or lower (down conversion) frequency.

26.     Frequency conversion is produced by a circuit called a mixer.

27.     Another name for frequency conversion is heterodyning.

28.     Almost any low-level AM circuit can be used for mixing.

29.     One of the most commonly used mixers is a single diode. Germanium or hot-carrier diodes are used for mixing at very high radio frequencies.

30.     The inputs to a mixer are the signal to be translated fs and a sine "wave fo from a local oscillator (LO). The outputs are fo, fs, fo + fs, and fo - fs. A tuned circuit at the output selects either the slim or difference frequency while suppressing the others. Any modulation on the input appears on the output signal.

31.     Bipolar and field-effect transistors can be used as mixers by operating them in the nonlinear region of their characteristics.

32.     Transistor mixers offer the benefit of gain over diode mixers.

33.     Balanced modulators are widely used as mixers.

34.     Doubly balanced modulators and GaAs FETs are the best mixers at VHF, UHF, and microwave frequencies.

35.     A single transistor can be connected to perform both the mixer and LO functions. Such a mixer is called a converter and is used primarily in AM receivers at frequencies below 30 MHz.

A popular IC mixer is the NE602, which contains a cross-connected differential amplifier mixer circuit and an on-chip local oscillator.

Frenzel Communications Electronics Summary Chapter 2

CHAPTER 2

Amplitude Modulation and Single-Sideband Modulation

1.        Modulation is the process of having the information to be communicated modifies a higher frequency signal called a carrier.

2.        Amplitude modulation (AM) is the oldest and simplest form of modulation.

3.        In AM, the amplitude of the carrier is changed in accordance with the amplitude and frequency or the characteristics of the modulating signal. The carrier frequency remains constant.

4.        The amplitude variation of the carrier peaks has the shape of the modulating signal and is referred to as the envelope.

5.        A time-domain display shows amplitude versus time variation of AM and other signals.

6.        Amplitude modulation is produced by a circuit called a modulator which has two in puts and an output.

7.        The modulator performs a mathematical multiplication of the carrier and information signals. The output is their analog product.

8.        The ratio of the peak voltage value of the modulating signal Vm to the peak value of the carrier Vc is called the modulation index m (m = Vm l Vc). It is also referred to as the modulation coefficient or factor and the degree of modulation.

9.        The ideal value for m is 1, Typically m is less than 1. The condition where m is greater than 1 should be avoided as it introduces serious distortion of the modulating signal. This is called overmodulation.

10.     When the modulation index is multiplied by 100, it is called the percentage of modulation.

11.     The percentage of modulation can be computed from AM waveforms displayed on an oscilloscope by using the expression

 

where  Vmax is the maximum peak carrier amplitude and

      Vmin is the minimum peak carrier amplitude.

12.     The new signals generated by the modulation process are called sidebands and occur at frequencies above and below the carrier frequency.

13.     The upper f_USB and lower f_LSB sideband frequencies are the sum and difference of the carrier frequency f_C and the modulating frequency f_M and are computed with the expressions

f_USB = fc + fm

f_LSB = fc – fm

14.     A display of signal amplitudes with respect to frequency is called a frequency-domain display.

15.     An AM signal can be viewed as the carrier signal added to the sideband signals produced by AM.

16.     The total transmitted power in an AM signal is the sum of the carrier and sideband powers P_T =( P_C + P_USB + P_LSB) and is distributed among the carrier and sidebands. This power distribution varies with the percentage of modulation. The total power is

P_T =P_e(1 + m²/2) 

The power in each sideband is 

P_s = P_c(m²)/4 

17.     The higher the percentage of modulation, the greater the sideband power and the stronger and more intelligible the transmitted and received signal.

18.     Despite its simplicity and effectiveness, AM is a highly inefficient method of modulation.

19.     In an AM signal, the carrier contains no information. Any transmitted information lies solely in the sideband. For that reason, the carrier may be suppressed and not transmitted.

20.     An AM signal with suppressed carrier is called a double-sideband (DSB) signal.

21.     Since the same transmitted information is contained in both upper and lower sidebands, one is redundant. Full information can be transmitted using only one sideband.

22.     An AM signal with no carrier and one sideband is called a single-sideband (SSB) signal. The upper and lower sidebands contain the same information, and one is not preferred over the other.

23.     The main advantage of an SSB AM signal over an AM or DSB signal is that it occupies one-half the spectrum space.

24.     Both DSB and SSB signals are more efficient in terms of power usage. The power wasted in the useless carrier is saved thereby allowing more power to be put into the sidebands.

25.     Power in an SSB transmitter is rated in terms of peak envelope power (PEP), the power that is produced on voice peaks. PEP output is computed using the expression

PEP = V²/R 

      where PEP is in watts and V is the rms voltage across the antenna load impedance R.  The PEP input is computed using the expression 

PEP = Vs x Imax 

      where Vs is the de supply voltage of the final amplifier stage and Imax is the amplifier  current on voice peaks. 

26.     The average output of an SSB transmitter is one-fourth to one-third of the PEP value.

27.     Frequency conversion is a form of AM used to translate signals to higher or lower frequencies for improved processing.

28.     Frequency conversion is carried out by a circuit called a mixer or converter.

29.     The mixer performs analog multiplication of the input signal and a local oscillator signal.

30.     The frequency conversion process faithfully retains any modulation (AM, PM, etc.) on the input. The translated signal contains the same modulation.

31.     The output of a mixer consists of the local oscillator signal fo and the sum and difference frequencies of the local oscillator and input frequencies:

f_S

fo

f_O + f_S

f_O - f_S or     f_S - f_O 

32.     Either the sum or the difference frequency is selected with a filter, while the others are rejected.

The process of mixing is also known as heterodyning.

kuya asan po ung mga questions ni Frenzel na 2nd edition. ung answers lng kasi ang nkita ko e pa send nmn po sa email ko marion_bernabe2000@y.c

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Frenzel Communications Electronics Chapter 1 Self Test / Exam

Self-Test
& Supply the missing word(s) in each statement.
    Choose the letter that best answers each question.

1.        The three major fields of electronics are _____. The largest is the _____field.

2.        Communication is defined as the process of _____.

3.        Most human communication is _____ even though there is a glut of _____ communication.

4.        Two major barriers to human communication are _____.

5.        Electronic communications came into being in the _____.

6.        The three main elements of any communications system are _____.

7.        The three major types of communications paths are_____.

8.        The _____ converts the message into a form compatible with the selected medium.

9.        The _____ converts the message from the medium into a form understandable by a human.

10.     Undesirable interference in communications _____ is which is added to the signal in the _____.

11.     The communications media greatly _____ and the information _____ signal.

12.     Three common sources of interference are _____.

13.     One-way communications is called_____. An example is _____.

14.     Simultaneous two-way communications is called _____. An example is _____.

15.     Two-way communications where each parry takes turns transmitting is referred to as_____.

16.     Voice and video signals are continuous _____ voltages.

17.     On/off or coded signals are referred to _____ as signals.

18.     Voice and video signals may be transmitted digitally if they are first passed through a(n) _____.

19.     An original voice, video, or data voltage is called the _____ signal.

20.     To make the transmitted signal compatible with the medium, the process of _____ must be used where the _____ signal is impressed upon a higher-frequency signal called the_____.

21.     Recovering the originally transmitted signal is called_____.

22.     The process of transmitting two or more baseband signals simultaneously over a common medium is called _____.

23.     Two methods of transmitting visual data over the telephone network are_____.

24.     A common household remote-control unit is the_____.

25.     The signaling of individuals at remote locations is called _____.

26.     Performing, recording, and analyzing measurements at a distance is done with _____ equipment.

27.     Radio astronomy is based on the fact that stars and other heavenly bodies emit_____.

28.     List four ways radio is used in the telephone system _____.

29.     Radar is based on the use of _____ radio signals.

30.     Underwater radar is called _____.

31.     The two types of sonar are _____.

32.     The radio communications hobby is called _____.

33.     Computers exchange digital data over the telephone network by using devices called _____.

34.     Limited interconnections of PCs and other computers in offices or buildings are called _____.

35.     Signals that travel through free space for long distances are called _____.

36.     Radio waves are made up of _____ fields.

37.     A signal with a frequency of 18 MHz has a wavelength of _____ m.

38.     Common power line frequencies of _____ and _____ Hz are in the _____ range.

39.     Audio signals are not transmitted by electromagnetic waves because

a.        Antennas would be too long.

b.        Audio signals do not radiate.

c.        Simultaneous transmissions would interfere.

d.        The frequency is too low.

   (Choose all that apply.)

40.     The human hearing range is approximately _____ to _____ Hz.

41.     The frequency range of the human voice is _____ to _____ Hz.

42.     True or false. Radio transmissions do not occur in the VLF and LF ranges.

43.     AM broadcast stations are in the _____ range.

44.     HF signals are also called _____.

45.     TV (channels 2 to 13) and FM broadcasting is in the _____ part of the spectrum.

46.     List five major uses of the UHF band.

47.     A frequency of 1 GHz is the same as _____ MHz.

48.     Frequencies above 1 GHz are called _____.

49.     The SHF and EHF ranges are primarily used by _____ communications.

50.     The frequencies just beyond the EHF range are called _____ waves.

51.     One micron is the same as _____ m.

52.     Infrared signals are usually derived from _____ sources.

53.     The spectrum range of infrared signals is _____ to _____ mm.

54.     One angstrom is equal to _____ mm.

55.     The visible light range is from _____ to _____Ǻ.

56.     Light signals use two mediums in electronic communications _____.

57.     The spectrum space occupied by a signal is called the _____.

58.     The new signals above and below the carrier frequency produced by the modulation process are called _____.

59.     A signal occupies the frequency range from 1.050 to 1.175 MHz. Its bandwidth is _____ kHz.

60.     Wide-bandwidth signals must be transmitted at _____ frequencies.

61.     Percentage wise, there is less spectrum space at the _____ frequencies.

62.     Many communications electronics techniques are designed in order to conserve _____.

63.     Electronic communications in the United States is regulated by a set of laws called the _____.

64.     The regulatory body for electronic communications in the United States is the _____.

65.     Government and military communications are coordinated by the _____.

The electromagnetic spectrum is managed worldwide by the_____ organization.