Understanding Radio Signals and Measurements
This article provides an overview of radio signals and measurements, focusing on sine waves as the most basic type of waveform. It explains the concept of cycles, frequencies, and periods in waveforms.
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About Understanding Radio Signals and Measurements
PowerPoint presentation about 'Understanding Radio Signals and Measurements'. This presentation describes the topic on This article provides an overview of radio signals and measurements, focusing on sine waves as the most basic type of waveform. It explains the concept of cycles, frequencies, and periods in waveforms.. The key topics included in this slideshow are Amateur Extra License Class, radio signals, measurements, sine waves, frequencies, periods,. Download this presentation absolutely free.
1. Amateur Extra License Class Chapter 7 Radio Signals and Measurements
2. Types of Waveforms Sine Waves Most basic type of waveform. Occur often in nature. Pendulum. Weight on spring. Point on rim of wheel.
3. Types of Waveforms Sine waves Contains only one frequency. Cycle = One complete set of values before they repeat. Cycle = One complete rotation of vector (360). Frequency = Number of cycles per second. Period = Time to complete one cycle.
4. Types of Waveforms Complex Waveforms Waveforms that contain more than one frequency. Regular waves. More properly called periodic waves. Repeat at a regular interval. Made up of a fundamental & its harmonics. Irregular waves. Non-periodic. Human speech. Easily visualized in frequency domain.
5. Types of Waveforms Sawtooth Wave Fundamental and all harmonics. Amplitude of harmonics decrease with increasing frequency. f 1 + f 2 /2 + f 3 /3 + f 4 /4 + f 5 /5 + ..
6. Types of Waveforms Square Wave Fundamental and all odd harmonics. Amplitude of harmonics decrease with increasing frequency. f 1 + f 3 /3 + f 5 /5 + f 7 /7 + f 9 /9 + ..
7. Types of Waveforms Rectangular Wave Square wave where on & off times are not equal. Pulse Wave Rectangular wave where position, width, and/or amplitude of pulses varies. In radio communications, often narrow pulses with wide gaps between pulses.
8. E8A01 -- What type of wave is made up of a sine wave plus all of its odd harmonics? A. A square wave B. A sine wave C. A cosine wave D. A tangent wave
9. E8A02 -- What type of wave has a rise time significantly faster than its fall time (or vice versa)? A. A cosine wave B. A square wave C. A sawtooth wave D. A sine wave
10. E8A03 -- What type of wave is made up of sine waves of a given fundamental frequency plus all its harmonics? A. A sawtooth wave B. A square wave C. A sine wave D. A cosine wave
11. E8A08 -- What is the period of a wave? A. The time required to complete one cycle B. The number of degrees in one cycle C. The number of zero crossings in one cycle D. The amplitude of the wave
12. E8A09 -- What type of waveform is produced by human speech? A. Sinusoidal B. Logarithmic C. Irregular D. Trapezoidal
13. E8A10 -- Which of the following is a distinguishing characteristic of a pulse waveform? A. Regular sinusoidal oscillations B. Narrow bursts of energy separated by periods of no signal C. A series of tones that vary between two frequencies D. A signal that contains three or more discrete tones
14. AC Waveforms and Measurements AC Measurements DC voltmeter/ammeter will read the average voltage/current, which is zero. With an oscilloscope, it is easy to read the maximum voltage/current. 1 = Peak 2 = Peak-to-Peak 3 = Root-Mean-Square (RMS)
15. AC Waveforms and Measurements AC Measurements An AC current will heat up a resistor. The amount of DC current that causes the same amount of heating is the root-mean- square (RMS) value. V RMS = 0.707 x V Peak 1 = Peak 2 = Peak-to-Peak 3 = Root-Mean-Square (RMS)
16. AC Waveforms and Measurements AC Measurements To Calculate Sine Wave Square Wave RMS 0.707 x Peak Peak Peak 1.414 x RMS RMS
17. AC Waveforms and Measurements AC Power Voltage & Current In-Phase P AVG = P RMS = V RMS x I RMS P Peak = V Peak x I Peak = 2 x P RMS
18. E8A04 -- What is equivalent to the root-mean- square value of an AC voltage? A. The AC voltage found by taking the square of the average value of the peak AC voltage B. The DC voltage causing the same amount of heating in a given resistor as the corresponding peak AC voltage C. The DC voltage causing the same amount of heating in a resistor as the corresponding RMS AC voltage D. The AC voltage found by taking the square root of the average AC value
19. E8A05 -- What would be the most accurate way of measuring the RMS voltage of a complex waveform? A. By using a grid dip meter B. By measuring the voltage with a D'Arsonval meter C. By using an absorption wavemeter D. By measuring the heating effect in a known resistor
20. E8D02 -- What is the relationship between the peak-to-peak voltage and the peak voltage amplitude of a symmetrical waveform? A. 0.707:1 B. 2:1 C. 1.414:1 D. 4:1
21. E8D03 -- What input-amplitude parameter is valuable in evaluating the signal-handling capability of a Class A amplifier? A. Peak voltage B. RMS voltage C. Average power D. Resting voltage
22. E8D05 -- If an RMS-reading AC voltmeter reads 65 volts on a sinusoidal waveform, what is the peak-to-peak voltage? A. 46 volts B. 92 volts C. 130 volts D. 184 volts
23. E8D12 -- What is the peak voltage of a sinusoidal waveform if an RMS-reading voltmeter reads 34 volts? A. 123 volts B. 96 volts C. 55 volts D. 48 volts
24. E8D13 -- Which of the following is a typical value for the peak voltage at a standard U.S. household electrical outlet? A. 240 volts B. 170 volts C. 120 volts D. 340 volts
25. E8D14 -- Which of the following is a typical value for the peak-to-peak voltage at a standard U.S. household electrical outlet? A. 240 volts B. 120 volts C. 340 volts D. 170 volts
26. E8D15 -- Which of the following is a typical value for the RMS voltage at a standard U.S. household electrical power outlet? A. 120V AC B. 340V AC C. 85V AC D. 170V AC
27. E8D16 -- What is the RMS value of a 340-volt peak-to-peak pure sine wave? A. 120V AC B. 170V AC C. 240V AC D. 300V AC
28. AC Waveforms and Measurements Power of Modulated RF Signals In an unmodulated RF signal, the average power can be calculated from: P AVG = V RMS 2 / Z
29. AC Waveforms and Measurements Power of Modulated RF Signals If the signal is modulated, the situation is more complex. CW, FM, & some digital modes have a constant amplitude & the average power is the same as if the carrier was not modulated. For other modes, it is more useful to use the peak envelope power (PEP) of the signal.
30. AC Waveforms and Measurements Power of Modulated RF Signals Modulated RF signals. Peak-Envelope-Power (PEP). Measure peak voltage. P PEP = (0.707 x V Peak ) 2 / R L Average Power. Long term average of power output. Crest Factor. Ratio of PEP to average power. SSB typically 2.5:1. 40%
31. E8A06 -- What is the approximate ratio of PEP- to-average power in a typical single-sideband phone signal? A. 2.5 to 1 B. 25 to 1 C. 1 to 1 D. 100 to 1
32. E8A07 -- What determines the PEP-to-average power ratio of a single-sideband phone signal? A. The frequency of the modulating signal B. The characteristics of the modulating signal C. The degree of carrier suppression D. The amplifier gain
33. E8D04 -- What is the PEP output of a transmitter that develops a peak voltage of 30 volts into a 50-ohm load? A. 4.5 watts B. 9 watts C. 16 watts D. 18 watts
34. E8D06 -- What is the advantage of using a peak- reading wattmeter to monitor the output of a SSB phone transmitter? A. It is easier to determine the correct tuning of the output circuit B. It gives a more accurate display of the PEP output when modulation is present C. It makes it easier to detect high SWR on the feed line D. It can determine if any flat-topping is present during modulation peaks
35. E8D10 -- What type of meter should be used to monitor the output signal of a voice-modulated single-sideband transmitter to ensure you do not exceed the maximum allowable power? A. An SWR meter reading in the forward direction B. A modulation meter C. An average reading wattmeter D. A peak-reading wattmeter
36. E8D11 -- What is the average power dissipated by a 50-ohm resistive load during one complete RF cycle having a peak voltage of 35 volts? A. 12.2 watts B. 9.9 watts C. 24.5 watts D. 16 watts
37. AC Waveforms and Measurements Electromagnetic Fields Electric field & magnetic field oscillating at right angles to each other. Travels through free space at the speed of light. 186,000 miles/second. 300 million meters/second.
38. AC Waveforms and Measurements Electromagnetic Fields Polarization. Defined by direction of electric field. Horizontal polarization Horizontal electric field. Vertical polarization Vertical electric field. Circular polarization Rotating electric field.
39. E8D07 -- What is an electromagnetic wave? A. Alternating currents in the core of an electromagnet B. A wave consisting of two electric fields at right angles to each other C. A wave consisting of an electric field and a magnetic field oscillating at right angles to each other D. A wave consisting of two magnetic fields at right angles to each other
40. E8D08 -- Which of the following best describes electromagnetic waves traveling in free space? A. Electric and magnetic fields become aligned as they travel B. The energy propagates through a medium with a high refractive index C. The waves are reflected by the ionosphere and return to their source D. Changing electric and magnetic fields propagate the energy
41. E8D09 -- What is meant by circularly polarized electromagnetic waves? A. Waves with an electric field bent into a circular shape B. Waves with a rotating electric field C. Waves that circle the Earth D. Waves produced by a loop antenna
42. Test Equipment Instruments and Accuracy Multimeters. a.k.a. VOM, DVM, VTVM. Accuracy expressed in % of full scale. If accuracy is 2% of full scale on 100 mA scale, then accuracy is + 2 mA. Resolution expressed in digits. Typically 3 digits (0.000 to 1.999) 3 digit 0.05% resolution. DO NOT CONFUSE RESOLUTION WITH ACCURACY!
43. Test Equipment Instruments and Accuracy Analog Multimeters. DArsonval movement. Rotating coil suspended between permanent magnets. When current flows in coil, coil rotates moving needle across scale. Coil impedance affects accuracy. Sensitivity expressed in Ohms/Volt. 20,000 /V very good analog meter.
44. Test Equipment Instruments and Accuracy Vacuum Tube Voltmeters (VTVM). DArsonval movement. Used vacuum tube amplifier to improve sensitivity. Typically 10 meg /V or greater.
45. Test Equipment Instruments and Accuracy Digital Multimeters (DVM). Digital display. Use FET amplifier to improve sensitivity. Typically 10 meg /V or greater.
46. Test Equipment Instruments and Accuracy Dip Meters. Oscillator with fixed external inductor & variable capacitor. External coil is coupled to an unknown tuned circuit & capacitor adjusted until dip occurs. Read resonant frequency from dial. General reading only not precision.
47. Test Equipment Instruments and Accuracy Dip Meters. Too loose coupling will not produce useable dip. Too tight coupling will change resonant frequency of circuit being measured.
48. Test Equipment Instruments and Accuracy Impedance bridges. By balancing the bridge you can determine value of unknown impedance. Null can be achieved very precisely. Antenna analyzers are actually impedance bridges.
49. Test Equipment Instruments and Accuracy Frequency counter. Accuracy dependent on time base Accuracy expressed in parts per million (ppm). May use a prescaler.
50. Test Equipment Instruments and Accuracy Frequency counter. Converts input signal into a series of pulses. Sometimes prescaler used to lower input frequency. Internal oscillator called the time base determines accuracy of counter.
51. Test Equipment Instruments and Accuracy Frequency counter. Direct-count frequency counter Counts number of pulses during a known time period. Frequency is calculated from number of pulses & length of gate pulse. Period-measuring frequency counter Counts number of time base pulses during one input signal pulse. Period is calculated from number of time-base pulses during one input signal pulse. Improved accuracy for low frequency signals.
52. E4B01 -- Which of the following factors most affects the accuracy of a frequency counter? A. Input attenuator accuracy B. Time base accuracy C. Decade divider accuracy D. Temperature coefficient of the logic
53. E4B02 -- What is an advantage of using a bridge circuit to measure impedance? A. It provides an excellent match under all conditions B. It is relatively immune to drift in the signal generator source C. The measurement is based on obtaining a signal null, which can be done very precisely D. It can display results directly in Smith chart format
54. E4B03 -- If a frequency counter with a specified accuracy of +/- 1.0 ppm reads 146,520,000 Hz, what is the most the actual frequency being measured could differ from the reading? A. 165.2 Hz B. 14.652 kHz C. 146.52 Hz D. 1.4652 MHz
55. E4B04 -- If a frequency counter with a specified accuracy of +/- 0.1 ppm reads 146,520,000 Hz, what is the most the actual frequency being measured could differ from the reading? A. 14.652 Hz B. 0.1 MHz C. 1.4652 Hz D. 1.4652 kHz
56. E4B05 -- If a frequency counter with a specified accuracy of +/- 10 ppm reads 146,520,000 Hz, what is the most the actual frequency being measured could differ from the reading? A. 146.52 Hz B. 10 Hz C. 146.52 kHz D. 1465.20 Hz
57. E4B08 -- Which of the following is a characteristic of a good DC voltmeter? A. High reluctance input B. Low reluctance input C. High impedance input D. Low impedance input
58. E4B12 -- What is the significance of voltmeter sensitivity expressed in ohms per volt? A. The full scale reading of the voltmeter multiplied by its ohms per volt rating will provide the input impedance of the voltmeter B. When used as a galvanometer, the reading in volts multiplied by the ohms/volt will determine the power drawn by the device under test C. When used as an ohmmeter, the reading in ohms divided by the ohms/volt will determine the voltage applied to the circuit D. When used as an ammeter, the full scale reading in amps divided by ohms/volt will determine the size of shunt needed
59. E4B14 -- What happens if a dip meter is too tightly coupled to a tuned circuit being checked? A. Harmonics are generated B. A less accurate reading results C. Cross modulation occurs D. Intermodulation distortion occurs
60. Test Equipment The Oscilloscope Allows direct observation of high-speed signals & waveforms.
61. Test Equipment The Oscilloscope Displays voltage versus time. Signal applied to vertical deflection plates. Sawtooth waveform from time base applied to horizontal deflection plates. Bandwidth of vertical amplifier determines highest frequency signal that can be displayed. Sometimes 2 or more vertical amplifiers. Allows displaying multiple signals simultaneously.
62. Test Equipment The Oscilloscope Uses a probe to connect signal to the vertical amplifier. Each probe has its own ground lead. Keep ground leads as short as possible. Probes are compensated to display high frequency waveforms accurately.
63. Test Equipment Probe Compensated Correctly
64. Test Equipment Probe Undercompensated
65. Test Equipment Probe Overcompensated
66. Test Equipment The Oscilloscope Easiest value to read using an oscilloscope is peak-to-peak voltage. Can also read: Peak voltage. Period.
67. Test Equipment Lissajous Pattern
68. E4A11 -- Which of these instruments could be used for detailed analysis of digital signals? A. Dip meter B. Oscilloscope C. Ohmmeter D. Q meter
69. E4B07 -- Which of the following is good practice when using an oscilloscope probe? A. Keep the signal ground connection of the probe as short as possible B. Never use a high impedance probe to measure a low impedance circuit C. Never use a DC-coupled probe to measure an AC circuit D. All of these choices are correct
70. E4B13 -- How is the compensation of an oscilloscope probe typically adjusted? A. A square wave is displayed and the probe is adjusted until the horizontal portions of the displayed wave are as nearly flat as possible B. A high frequency sine wave is displayed and the probe is adjusted for maximum amplitude C. A frequency standard is displayed and the probe is adjusted until the deflection time is accurate D. A DC voltage standard is displayed and the probe is adjusted until the displayed voltage is accurate
71. E8D01 -- Which of the following is the easiest voltage amplitude parameter to measure when viewing a pure sine wave signal on an analog oscilloscope? A. Peak-to-peak voltage B. RMS voltage C. Average voltage D. DC voltage
72. Test Equipment The Spectrum Analyzer
73. Test Equipment The Spectrum Analyzer Displays signal amplitude versus frequency. An oscilloscope displays signals in the time domain. Horizontal axis displays time. A spectrum analyzer displays signals in the frequency domain. Horizontal axis displays frequency. Narrow filter swept across a range of frequencies.
74. The Spectrum Analyzer Used for checking output of transmitter or amplifier for spurs. Used for checking transmitter intermodulation distortion (IMD). Test Equipment
75. Test Equipment The Spectrum Analyzer
76. Test Equipment
77. Test Equipment
78. Test Equipment
79. Test Equipment Two-tone Intermodulation Distortion (IMD) Test 2 non-harmonically related tones. ARRL Labs uses 700 Hz & 1900 Hz.
80. E4A01 -- How does a spectrum analyzer differ from an oscilloscope? A. A spectrum analyzer measures ionospheric reflection; an oscilloscope displays electrical signals B. A spectrum analyzer displays the peak amplitude of signals; an oscilloscope displays the average amplitude of signals C. A spectrum analyzer displays signals in the frequency domain; an oscilloscope displays signals in the time domain D. A spectrum analyzer displays radio frequencies; an oscilloscope displays audio frequencies
81. E4A02 -- Which of the following parameters would a spectrum analyzer display on the horizontal axis? A. SWR B. Q C. Time D. Frequency
82. E4A03 -- Which of the following parameters would a spectrum analyzer display on the vertical axis? A. Amplitude B. Duration C. SWR D. Q
83. E4A04 -- Which of the following test instruments is used to display spurious signals from a radio transmitter? A. A spectrum analyzer B. A wattmeter C. A logic analyzer D. A time-domain reflectometer
84. E4A05 -- Which of the following test instruments is used to display intermodulation distortion products in an SSB transmission? A. A wattmeter B. A spectrum analyzer C. A logic analyzer D. A time-domain reflectometer
85. E4A06 -- Which of the following could be determined with a spectrum analyzer? A. The degree of isolation between the input and output ports of a 2 meter duplexer B. Whether a crystal is operating on its fundamental or overtone frequency C. The spectral output of a transmitter D. All of these choices are correct
86. E4A12 -- Which of the following procedures is an important precaution to follow when connecting a spectrum analyzer to a transmitter output? A. Use high quality double shielded coaxial cables to reduce signal losses B. Attenuate the transmitter output going to the spectrum analyzer C. Match the antenna to the load D. All of these choices are correct
87. E4B10 -- Which of the following describes a method to measure intermodulation distortion in an SSB transmitter? A. Modulate the transmitter with two non-harmonically related radio frequencies and observe the RF output with a spectrum analyzer B. Modulate the transmitter with two non-harmonically related audio frequencies and observe the RF output with a spectrum analyzer C. Modulate the transmitter with two harmonically related audio frequencies and observe the RF output with a peak reading wattmeter D. Modulate the transmitter with two harmonically related audio frequencies and observe the RF output with a logic analyzer
88. Transistor Circuit Parameters Some DC voltage measurements are useful for troubleshooting. V BE ~ 0.7 V DC (Silicon) V BE ~ 0.3 V DC (Germanium) V CE ~ 0.5 x V CC (If class A amplifier.) Other examples in book. Test Equipment
89. E4A10 -- Which of the following tests establishes that a silicon NPN junction transistor is biased on? A. Measure base-to-emitter resistance with an ohmmeter; it should be approximately 6 to 7 ohms B. Measure base-to-emitter resistance with an ohmmeter; it should be approximately 0.6 to 0.7 ohms C. Measure base-to-emitter voltage with a voltmeter; it should be approximately 6 to 7 volts D. Measure base-to-emitter voltage with a voltmeter; it should be approximately 0.6 to 0.7 volts
91. Modulation Systems FCC Emission Designations and Terms Specified by ITU. Either 3 or 7 characters. If 3 characters: 1 st Character - type of modulation of the main carrier. 2 nd Character - nature of signal(s) modulating the main carrier. 3 rd Character - type of information to be transmitted. If 7 characters, add 4-character bandwidth designator in front of 3-character designator.
92. Modulation Systems FCC Emission Designations and Terms Type of Modulation. N Unmodulated Carrier A Amplitude Modulation R Single Sideband Reduced Carrier J Single Sideband Suppressed Carrier C Vestigial Sideband F Frequency Modulation G Phase Modulation P, K, L, M, Q, V, W, X Various Types of Pulse Modulation
93. Modulation Systems FCC Emission Designations and Terms Type of Modulating Signal. 0 No modulating signal 1 A single channel containing quantized or digital information without the use of a modulating sub-carrier 2 A single channel containing quantized or digital information with the use of a modulating sub-carrier 3 A single channel containing analogue information 7 Two or more channels containing quantized or digital information 8 Two or more channels containing analogue information X Cases not otherwise covered
94. Modulation Systems FCC Emission Designations and Terms Type of Transmitted Information. N No information transmitted A Telegraphy - for aural reception B Telegraphy - for automatic reception C Facsimile D Data transmission, telemetry, telecommand E Telephony (including sound broadcasting) F Television (video) W Combination of the above X Cases not otherwise covered
95. Modulation Systems FCC Emission Designations and Terms 3-character designator examples: A1A = CW. A3E = Amplitude-modulated phone. J3E = Single-sideband phone. F3E = Frequency-modulated phone. F1B = Radioteletype (RTTY).
96. Modulation Systems FCC Emission Designations and Terms Emission Types. Part 97 refers to emission types rather than emission designators. Continuous Wave (CW) Modulated CW (MCW) Phone (AM, FM, SSB) Spread Spectrum (SS) Radiotetetype (RTTY) Pulse Data (Packet, PSK-31, etc.) Test Image (SSTV, Fascimile, etc.)
97. Modulation Systems FM/PM Modulation and Modulators Amount of frequency change is proportional to amplitude of modulating signal. Deviation. Speed of frequency change is equal to frequency of modulating signal. Need to understand 2 terms to fully describe an FM or PM signal. Deviation Ratio. Modulation Index.
98. Modulation Systems FM/PM Modulation and Modulators Deviation ratio. Deviation Ratio = f Dev / f Mod f Dev = Maximum frequency deviation. f Mod = Maximum modulating frequency. Deviation ratio is constant in both an FM modulator and in a PM modulator.
99. Modulation Systems FM/PM Modulation and Modulators Modulation index. Modulation Index = f Dev / f m f Dev = Maximum frequency deviation. f m = Instantaneous modulating frequency. Modulation index is continuously changing with modulating frequency in an FM modulator. Modulation index is constant in a PM modulator. The FCC Rules limit the modulation index to 1.0 at the highest modulating frequency. [97.307(f)(1)]
100. E1B12 -- What is the highest modulation index permitted at the highest modulation frequency for angle modulation? A. .5 B. 1.0 C. 2.0 D. 3.0
101. E8B01 -- What is the term for the ratio between the frequency deviation of an RF carrier wave, and the modulating frequency of its corresponding FM-phone signal? A. FM compressibility B. Quieting index C. Percentage of modulation D. Modulation index
102. E8B02 -- How does the modulation index of a phase-modulated emission vary with RF carrier frequency (the modulated frequency)? A. It increases as the RF carrier frequency increases B. It decreases as the RF carrier frequency increases C. It varies with the square root of the RF carrier frequency D. It does not depend on the RF carrier frequency
103. E8B03 -- What is the modulation index of an FM-phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency, when the modulating frequency is 1000 Hz? A. 3 B. 0.3 C. 3000 D. 1000
104. E8B04 -- What is the modulation index of an FM-phone signal having a maximum carrier deviation of plus or minus 6 kHz when modulated with a 2-kHz modulating frequency? A. 6000 B. 3 C. 2000 D. 1/3
105. E8B05 -- What is the deviation ratio of an FM- phone signal having a maximum frequency swing of plus-or-minus 5 kHz when the maximum modulation frequency is 3 kHz? A. 60 B. 0.167 C. 0.6 D. 1.67
106. E8B06 -- What is the deviation ratio of an FM- phone signal having a maximum frequency swing of plus or minus 7.5 kHz when the maximum modulation frequency is 3.5 kHz? A. 2.14 B. 0.214 C. 0.47 D. 47
107. E8B09 -- What is meant by deviation ratio? A. The ratio of the audio modulating frequency to the center carrier frequency B. The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency C. The ratio of the carrier center frequency to the audio modulating frequency D. The ratio of the highest audio modulating frequency to the average audio modulating frequency
108. Modulation Systems Pulse Modulation Systems. Series of widely spaced short pulses. Peak power greater than average power. Signal duty cycle < 100%. Often used for data transmission.
109. Modulation Systems Pulse Modulation Systems. Types of pulse modulation. Pulse amplitude modulation (PAM). Pulse width modulation (PWM). a.k.a. Pulse duration modulation (PDM). Pulse position modulation (PPM). Pulse code modulation (PCM).
110. Modulation Systems Pulse Modulation Systems. Pulse amplitude modulation (PAM). Varies amplitude of pulses.
111. Modulation Systems Pulse Modulation Systems. Pulse width modulation (PWM). Varies width of pulses.
112. Modulation Systems Pulse Modulation Systems. Pulse position modulation (PPM). Varies time at which pulses occur.
113. Modulation Systems Pulse Modulation Systems. Pulse code modulation (PCM). Transmits series of binary-coded pulses.
114. E8A11 -- What is one use for a pulse modulated signal? A. Linear amplification B. PSK31 data transmission C. Multiphase power transmission D. Digital data transmission
115. E8B07 -- When using a pulse-width modulation system, why is the transmitter's peak power greater than its average power? A. The signal duty cycle is less than 100% B. The signal reaches peak amplitude only when voice modulated C. The signal reaches peak amplitude only when voltage spikes are generated within the modulator D. The signal reaches peak amplitude only when the pulses are also amplitude modulated
116. E8B08 -- What parameter does the modulating signal vary in a pulse-position modulation system? A. The number of pulses per second B. The amplitude of the pulses C. The duration of the pulses D. The time at which each pulse occurs
117. Modulation Systems Multiplexing. Transmitting multiple, independent signals on one carrier.
118. Modulation Systems Multiplexing. Frequency-division multiplexing. One or more sub-carriers, each carrying a different signal. Commercial FM broadcast SCA. VHF Omni-Range (VOR). Fiber optics.
119. Modulation Systems Multiplexing. Time-division multiplexing. Signals are sampled & samples from each signal are interleaved in sequential time slots. Normally digital transmission. Telemetry.
120. E8B10 -- Which of these methods can be used to combine several separate analog information streams into a single analog radio frequency signal? A. Frequency shift keying B. A diversity combiner C. Frequency division multiplexing D. Pulse compression
121. E8B11 -- Which of the following describes frequency division multiplexing? A. The transmitted signal jumps from band to band at a predetermined rate B. Two or more information streams are merged into a "baseband", which then modulates the transmitter C. The transmitted signal is divided into packets of information D. Two or more information streams are merged into a digital combiner, which then pulse position modulates the transmitter
122. E8B12 -- What is digital time division multiplexing? A. Two or more data streams are assigned to discrete sub-carriers on an FM transmitter B. Two or more signals are arranged to share discrete time slots of a data transmission C. Two or more data streams share the same channel by transmitting time of transmission as the sub-carrier D. Two or more signals are quadrature modulated to increase bandwidth efficiency
123. Interference and Noise Intermodulation Non-linear circuits or components can act as mixers to generate signals at the sums & differences of the signals being mixed. Unwanted signal can be heard along with wanted signal. Signals can also mix in corroded metal junctions or junctions of dissimilar metals.
124. Interference and Noise Transmitter Intermodulation Signals can mix in the output stage of a transmitter. The IMD products can be transmitted along with the desired signal. Low-pass or high-pass filters are NOT effective. Circulators & isolators are used. Ferrite devices that act like one-way valves for RF. Cavity resonators.
125. E4D03 -- How can intermodulation interference between two repeaters occur? A. When the repeaters are in close proximity and the signals cause feedback in the final amplifier of one or both transmitters B. When the repeaters are in close proximity and the signals mix in the final amplifier of one or both transmitters C. When the signals from the transmitters are reflected out of phase from airplanes passing overhead D. When the signals from the transmitters are reflected in phase from airplanes passing overhead
126. E4D04 -- Which of the following may reduce or eliminate intermodulation interference in a repeater caused by another transmitter operating in close proximity? A. A band-pass filter in the feed line between the transmitter and receiver B. A properly terminated circulator at the output of the transmitter C. A Class C final amplifier D. A Class D final amplifier
127. E4D06 -- What is the term for unwanted signals generated by the mixing of two or more signals? A. Amplifier desensitization B. Neutralization C. Adjacent channel interference D. Intermodulation interference
128. E4D07 -- Which of the following describes the most significant effect of an off-frequency signal when it is causing cross-modulation interference to a desired signal? A. A large increase in background noise B. A reduction in apparent signal strength C. The desired signal can no longer be heard D. The off-frequency unwanted signal is heard in addition to the desired signal
129. E4D08 -- What causes intermodulation in an electronic circuit? A. Too little gain B. Lack of neutralization C. Nonlinear circuits or devices D. Positive feedback
130. E4E11 -- Which of the following is the most likely cause if you are hearing combinations of local AM broadcast signals within one or more of the MF or HF ham bands? A. The broadcast station is transmitting an over- modulated signal B. Nearby corroded metal joints are mixing and re- radiating the broadcast signals C. You are receiving sky wave signals from a distant station D. Your station receiver IF amplifier stage is defective
131. Interference and Noise Atmospheric Static Discharge of static electricity in the atmosphere. Lightning most visible source of static discharge, but non-lightning discharges occur all the time. Thunderstorm static louder on lower HF bands (160m, 80m, & 40m). Can be heard several hundred miles from the source.
132. Interference and Noise Atmospheric Static Static noise can occur without a thunderstorm. Rain static. Snow static. Wind static.
133. E4E06 -- What is a major cause of atmospheric static? A. Solar radio frequency emissions B. Thunderstorms C. Geomagnetic storms D. Meteor showers
134. Interference and Noise AC Line Noise Man-made noise caused by electric arc. Electric motors. Light dimmers. Neon signs. Defective doorbell or doorbell transformer.
135. Interference and Noise AC Line Noise Install brute force AC line filter in series with motor power leads.
136. E4E05 -- How can noise from an electric motor be suppressed? A. By installing a high pass filter in series with the motors power leads B. By installing a brute-force AC-line filter in series with the motor leads C. By installing a bypass capacitor in series with the motor leads D. By using a ground-fault current interrupter in the circuit used to power the motor
137. E4E13 -- What might be the cause of a loud roaring or buzzing AC line interference that comes and goes at intervals? A. Arcing contacts in a thermostatically controlled device B. A defective doorbell or doorbell transformer inside a nearby residence C. A malfunctioning illuminated advertising display D. All of these choices are correct
138. Interference and Noise Locating Noise and Interference Sources Interference from inside building usually conducted through AC power wiring. Inside your house. Outside your house.
139. Interference and Noise Locating Noise and Interference Sources To determine if noise is generated within your own house, pull main breaker & listen on a battery-operated receiver. Not FM receiver. Restore power & make certain noise returns. Offending device may need to be powered on for a while before generating noise. Remove power one circuit at a time until noise disappears.
140. Interference and Noise Locating Noise and Interference Sources Interference from outside building usually picked up by antenna or transmission line. Use fox hunting techniques to locate source.
141. Interference and Noise Locating Noise and Interference Sources Your transmitter can couple RF into AC and/or telephone wiring & cause interference to other devices. Common mode signals. RF flowing in same direction on both conductors. Install common mode choke. Several turns of wire around ferrite toroid core.
142. Interference and Noise Locating Noise and Interference Sources Computer & networking devices. Unstable modulated or unmodulated signals at specific frequencies. Switching power supplies. Series of signals spaced at regular intervals over a wide spectrum. Touch-controlled devices. Same as above plus signals that sound like AC hum that may drift slowly across the band.
143. Interference and Noise Locating Noise and Interference Sources Plasma TVs.
144. E4E07 -- How can you determine if line noise interference is being generated within your home? A. By checking the power line voltage with a time domain reflectometer B. By observing the AC power line waveform with an oscilloscope C. By turning off the AC power line main circuit breaker and listening on a battery operated radio D. By observing the AC power line voltage with a spectrum analyzer
145. E4E08 -- What type of signal is picked up by electrical wiring near a radio antenna? A. A common-mode signal at the frequency of the radio transmitter B. An electrical-sparking signal C. A differential-mode signal at the AC power line frequency D. Harmonics of the AC power line frequency
146. E4E10 -- What is a common characteristic of interference caused by a touch controlled electrical device? A. The interfering signal sounds like AC hum on an AM receiver or a carrier modulated by 60 Hz hum on a SSB or CW receiver B. The interfering signal may drift slowly across the HF spectrum C. The interfering signal can be several kHz in width and usually repeats at regular intervals across a HF band D. All of these choices are correct
147. E4E14 -- What is one type of electrical interference that might be caused by the operation of a nearby personal computer? A. A loud AC hum in the audio output of your station receiver B. A clicking noise at intervals of a few seconds C. The appearance of unstable modulated or unmodulated signals at specific frequencies D. A whining type noise that continually pulses off and on
148. Interference and Noise Automotive Noise Vehicular System Noise Ignition system noise. Pre-1975. Resistance spark plugs. High-resistance spark plug cables. Shielded cables. 1975 & later. High resistance plugs & cables can degrade engine performance.
149. Interference and Noise Automotive Noise Vehicular System Noise Charging system noise. High-pitched whine or buzz. Changes frequency with engine speed. Radiated & picked up by antenna. Conducted through power wiring. Connect radio power leads directly to battery. Fuse EACH lead. Add coaxial capacitors in alternator leads. a.k.a. Feed-through capacitors.
150. Interference and Noise Automotive Noise Vehicular System Noise Instrument noise. Some instruments can generate RF noise. Install 0.5 F coaxial capacitor at the sender element. Wiper, fuel pump, & other motors can generate RF noise. Install 0.25 F capacitor across the motor winding.
151. E4E04 -- How can conducted and radiated noise caused by an automobile alternator be suppressed? A. By installing filter capacitors in series with the DC power lead and by installing a blocking capacitor in the field lead B. By installing a noise suppression resistor and a blocking capacitor in both leads C. By installing a high-pass filter in series with the radio's power lead and a low-pass filter in parallel with the field lead D. By connecting the radio's power leads directly to the battery and by installing coaxial capacitors in line with the alternator leads
152. Interference and Noise Noise Reduction Noise Blankers Detects noise pulse & interrupts signal during duration of pulse. a.k.a. Gating. Particularly effective for power line or ignition noise. Must see signals that appear across a wide bandwidth. Strong nearby signals may appear excessively wide.
153. Interference and Noise Noise Reduction DSP Noise Reduction. Use adaptive filter techniques. Looks for signals that have characteristics of CW or SSB signals & remove everything else. Works well with ALL types of noise & interference.
154. Interference and Noise Noise Reduction DSP Noise Reduction. Automatic Notch Filters (ANF). Very effective in eliminating interference from a strong steady signal (carrier) in the receive passband. Not recommended for copying CW or low data rate digital signals. A good ANF will notch out the desired signal.
155. E4E01 -- Which of the following types of receiver noise can often be reduced by use of a receiver noise blanker? A. Ignition noise B. Broadband white noise C. Heterodyne interference D. All of these choices are correct
156. E4E02 -- Which of the following types of receiver noise can often be reduced with a DSP noise filter? A. Broadband white noise B. Ignition noise C. Power line noise D. All of these choices are correct
157. E4E03 -- Which of the following signals might a receiver noise blanker be able to remove from desired signals? A. Signals which are constant at all IF levels B. Signals which appear across a wide bandwidth C. Signals which appear at one IF but not another D. Signals which have a sharply peaked frequency distribution
158. E4E09 -- What undesirable effect can occur when using an IF noise blanker? A. Received audio in the speech range might have an echo effect B. The audio frequency bandwidth of the received signal might be compressed C. Nearby signals may appear to be excessively wide even if they meet emission standards D. FM signals can no longer be demodulated
159. E4E12 -- What is one disadvantage of using some types of automatic DSP notch-filters when attempting to copy CW signals? A. The DSP filter can remove the desired signal at the same time as it removes interfering signals B. Any nearby signal passing through the DSP system will overwhelm the desired signal C. Received CW signals will appear to be modulated at the DSP clock frequency D. Ringing in the DSP filter will completely remove the spaces between the CW characters