Presentation on theme: "Amateur Extra License Class"— Presentation transcript:
1Amateur Extra License Class Chapter 7Radio Signals and Measurements
2Types of Waveforms Sine Waves Most basic type of waveform. Occur often in nature.Pendulum.Weight on spring.Point on rim of wheel.
3Types 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.
4Types 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.
5Types of Waveforms Sawtooth Wave Fundamental and all harmonics. Amplitude of harmonics decrease with increasing frequency.f1 + f2/2 + f3/3 + f4/4 + f5/5 + ………..
6Types of Waveforms Square Wave Fundamental and all odd harmonics. Amplitude of harmonics decrease with increasing frequency.f1 + f3/3 + f5/5 + f7/7 + f9/9 + ………..
7Types of Waveforms Rectangular Wave Pulse Wave Square wave where on & off times are not equal.Pulse WaveRectangular wave where position, width, and/or amplitude of pulses varies.In radio communications, often narrow pulses with wide gaps between pulses.
8E8A01 -- What type of wave is made up of a sine wave plus all of its odd harmonics? A square waveA sine waveA cosine waveA tangent wave
9E8A02 -- What type of wave has a rise time significantly faster than its fall time (or vice versa)? A cosine waveA square waveA sawtooth waveA sine wave
10E8A03 -- What type of wave is made up of sine waves of a given fundamental frequency plus all its harmonics?A sawtooth waveA square waveA sine waveA cosine wave
11E8A08 -- What is the period of a wave? The time required to complete one cycleThe number of degrees in one cycleThe number of zero crossings in one cycleThe amplitude of the wave
12E8A09 -- What type of waveform is produced by human speech? SinusoidalLogarithmicIrregularTrapezoidal
13E8A10 -- Which of the following is a distinguishing characteristic of a pulse waveform? Regular sinusoidal oscillationsNarrow bursts of energy separated by periods of no signalA series of tones that vary between two frequenciesA signal that contains three or more discrete tones
14AC Waveforms and Measurements AC MeasurementsDC voltmeter/ammeter will read the average voltage/current, which is zero.With an oscilloscope, it is easy to read the maximum voltage/current.1 = Peak2 = Peak-to-Peak3 = Root-Mean-Square (RMS)
15AC Waveforms and Measurements AC MeasurementsAn 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.VRMS = x VPeak1 = Peak2 = Peak-to-Peak3 = Root-Mean-Square (RMS)
16AC Waveforms and Measurements AC MeasurementsTo CalculateSine WaveSquare WaveRMS0.707 x PeakPeak1.414 x RMS
17AC Waveforms and Measurements AC PowerVoltage & Current In-PhasePAVG = PRMS = VRMS x IRMSPPeak = VPeak x IPeak = 2 x PRMS
18E8A04 -- What is equivalent to the root-mean-square value of an AC voltage? The AC voltage found by taking the square of the average value of the peak AC voltageThe DC voltage causing the same amount of heating in a given resistor as the corresponding peak AC voltageThe DC voltage causing the same amount of heating in a resistor as the corresponding RMS AC voltageThe AC voltage found by taking the square root of the average AC value
19E8A05 -- What would be the most accurate way of measuring the RMS voltage of a complex waveform? By using a grid dip meterBy measuring the voltage with a D'Arsonval meterBy using an absorption wavemeterBy measuring the heating effect in a known resistor
20E8D02 -- What is the relationship between the peak-to-peak voltage and the peak voltage amplitude of a symmetrical waveform?0.707:12:11.414:14:1
21E8D03 -- What input-amplitude parameter is valuable in evaluating the signal-handling capability of a Class A amplifier?Peak voltageRMS voltageAverage powerResting voltage
22E8D05 -- If an RMS-reading AC voltmeter reads 65 volts on a sinusoidal waveform, what is the peak-to-peak voltage?46 volts92 volts130 volts184 volts
23E8D12 -- What is the peak voltage of a sinusoidal waveform if an RMS-reading voltmeter reads 34 volts?123 volts96 volts55 volts48 volts
24E8D13 -- Which of the following is a typical value for the peak voltage at a standard U.S. household electrical outlet?240 volts170 volts120 volts340 volts
25E8D14 -- Which of the following is a typical value for the peak-to-peak voltage at a standard U.S. household electrical outlet?240 volts120 volts340 volts170 volts
26E8D15 -- Which of the following is a typical value for the RMS voltage at a standard U.S. household electrical power outlet?120V AC340V AC85V AC170V AC
27E8D16 -- What is the RMS value of a 340-volt peak-to-peak pure sine wave? 120V AC170V AC240V AC300V AC
28AC Waveforms and Measurements Power of Modulated RF SignalsIn an unmodulated RF signal, the average power can be calculated from:PAVG = VRMS2 / Z
29AC Waveforms and Measurements Power of Modulated RF SignalsIf 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.
30AC Waveforms and Measurements Power of Modulated RF SignalsModulated RF signals.Peak-Envelope-Power (PEP).Measure peak voltage.PPEP = (0.707 x VPeak)2 / RLAverage Power.Long term average of power output.Crest Factor.Ratio of PEP to average power.SSB typically 2.5:1.40%
31E8A06 -- What is the approximate ratio of PEP-to-average power in a typical single-sideband phone signal?2.5 to 125 to 11 to 1100 to 1
32E8A07 -- What determines the PEP-to-average power ratio of a single-sideband phone signal? The frequency of the modulating signalThe characteristics of the modulating signalThe degree of carrier suppressionThe amplifier gain
33E8D04 -- What is the PEP output of a transmitter that develops a peak voltage of 30 volts into a 50-ohm load?4.5 watts9 watts16 watts18 watts
34E8D06 -- What is the advantage of using a peak-reading wattmeter to monitor the output of a SSB phone transmitter?It is easier to determine the correct tuning of the output circuitIt gives a more accurate display of the PEP output when modulation is presentIt makes it easier to detect high SWR on the feed lineIt can determine if any flat-topping is present during modulation peaks
35E8D10 -- 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?An SWR meter reading in the forward directionA modulation meterAn average reading wattmeterA peak-reading wattmeter
36E8D11 -- What is the average power dissipated by a 50-ohm resistive load during one complete RF cycle having a peak voltage of 35 volts?12.2 watts9.9 watts24.5 watts16 watts
37AC Waveforms and Measurements Electromagnetic FieldsElectric 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.
38AC Waveforms and Measurements Electromagnetic FieldsPolarization.Defined by direction of electric field.Horizontal polarization Horizontal electric field.Vertical polarization Vertical electric field.Circular polarization Rotating electric field.
39E8D07 -- What is an electromagnetic wave? Alternating currents in the core of an electromagnetA wave consisting of two electric fields at right angles to each otherA wave consisting of an electric field and a magnetic field oscillating at right angles to each otherA wave consisting of two magnetic fields at right angles to each other
40E8D08 -- Which of the following best describes electromagnetic waves traveling in free space? Electric and magnetic fields become aligned as they travelThe energy propagates through a medium with a high refractive indexThe waves are reflected by the ionosphere and return to their sourceChanging electric and magnetic fields propagate the energy
41E8D09 -- What is meant by circularly polarized electromagnetic waves? Waves with an electric field bent into a circular shapeWaves with a rotating electric fieldWaves that circle the EarthWaves produced by a loop antenna
42Test 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 ½ digits (0.000 to 1.999)3 ½ digit 0.05% resolution.DO NOT CONFUSE RESOLUTION WITH ACCURACY!
43Test Equipment Instruments and Accuracy Analog Multimeters. D’Arsonval 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 Ω/V very good analog meter.
44Test Equipment Instruments and Accuracy Vacuum Tube Voltmeters (VTVM). D’Arsonval movement.Used vacuum tube amplifier to improve sensitivity.Typically 10 megΩ/V or greater.
45Test Equipment Instruments and Accuracy Digital Multimeters (DVM). Digital display.Use FET amplifier to improve sensitivity.Typically 10 megΩ/V or greater.
46Test 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.
47Test 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.
48Test 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.
49Test Equipment Instruments and Accuracy Frequency counter. Accuracy dependent on time baseAccuracy expressed in parts per million (ppm).May use a prescaler.
50Test 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.
51Test Equipment Instruments and Accuracy Frequency counter. Direct-count frequency counterCounts number of pulses during a known time period.Frequency is calculated from number of pulses & length of gate pulse.Period-measuring frequency counterCounts 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.
52E4B01 -- Which of the following factors most affects the accuracy of a frequency counter? Input attenuator accuracyTime base accuracyDecade divider accuracyTemperature coefficient of the logic
53E4B02 -- What is an advantage of using a bridge circuit to measure impedance? It provides an excellent match under all conditionsIt is relatively immune to drift in the signal generator sourceThe measurement is based on obtaining a signal null, which can be done very preciselyIt can display results directly in Smith chart format
54E4B03 -- If a frequency counter with a specified accuracy of +/- 1 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?165.2 HzkHzHzMHz
55E4B04 -- If a frequency counter with a specified accuracy of +/- 0 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?Hz0.1 MHzHzkHz
56E4B05 -- 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?Hz10 HzkHzHz
57E4B08 -- Which of the following is a characteristic of a good DC voltmeter? High reluctance inputLow reluctance inputHigh impedance inputLow impedance input
58E4B12 -- What is the significance of voltmeter sensitivity expressed in ohms per volt? The full scale reading of the voltmeter multiplied by its ohms per volt rating will provide the input impedance of the voltmeterWhen used as a galvanometer, the reading in volts multiplied by the ohms/volt will determine the power drawn by the device under testWhen used as an ohmmeter, the reading in ohms divided by the ohms/volt will determine the voltage applied to the circuitWhen used as an ammeter, the full scale reading in amps divided by ohms/volt will determine the size of shunt needed
59E4B14 -- What happens if a dip meter is too tightly coupled to a tuned circuit being checked? Harmonics are generatedA less accurate reading resultsCross modulation occursIntermodulation distortion occurs
60Test Equipment The Oscilloscope Allows direct observation of high-speed signals & waveforms.
61Test 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.
62Test 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.
63Probe Compensated Correctly Test EquipmentProbe Compensated Correctly
64Probe Undercompensated Test EquipmentProbe Undercompensated
65Probe Overcompensated Test EquipmentProbe Overcompensated
66Test Equipment The Oscilloscope Easiest value to read using an oscilloscope is peak-to-peak voltage.Can also read:Peak voltage.Period.
68E4A11 -- Which of these instruments could be used for detailed analysis of digital signals? Dip meterOscilloscopeOhmmeterQ meter
69E4B07 -- Which of the following is good practice when using an oscilloscope probe? Keep the signal ground connection of the probe as short as possibleNever use a high impedance probe to measure a low impedance circuitNever use a DC-coupled probe to measure an AC circuitAll of these choices are correct
70E4B13 -- How is the compensation of an oscilloscope probe typically adjusted? A square wave is displayed and the probe is adjusted until the horizontal portions of the displayed wave are as nearly flat as possibleA high frequency sine wave is displayed and the probe is adjusted for maximum amplitudeA frequency standard is displayed and the probe is adjusted until the deflection time is accurateA DC voltage standard is displayed and the probe is adjusted until the displayed voltage is accurate
71E8D01 -- Which of the following is the easiest voltage amplitude parameter to measure when viewing a pure sine wave signal on an analog oscilloscope?Peak-to-peak voltageRMS voltageAverage voltageDC voltage
73Test 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.
74Test Equipment The Spectrum Analyzer Used for checking output of transmitter or amplifier for spurs.Used for checking transmitter intermodulation distortion (IMD).
79Test Equipment Two-tone Intermodulation Distortion (IMD) Test 2 non-harmonically related tones.ARRL Labs uses 700 Hz & 1900 Hz.
80E4A01 -- How does a spectrum analyzer differ from an oscilloscope? A spectrum analyzer measures ionospheric reflection; an oscilloscope displays electrical signalsA spectrum analyzer displays the peak amplitude of signals; an oscilloscope displays the average amplitude of signalsA spectrum analyzer displays signals in the frequency domain; an oscilloscope displays signals in the time domainA spectrum analyzer displays radio frequencies; an oscilloscope displays audio frequencies
81E4A02 -- Which of the following parameters would a spectrum analyzer display on the horizontal axis? SWRQTimeFrequency
82E4A03 -- Which of the following parameters would a spectrum analyzer display on the vertical axis? AmplitudeDurationSWRQ
83E4A04 -- Which of the following test instruments is used to display spurious signals from a radio transmitter?A spectrum analyzerA wattmeterA logic analyzerA time-domain reflectometer
84E4A05 -- Which of the following test instruments is used to display intermodulation distortion products in an SSB transmission?A wattmeterA spectrum analyzerA logic analyzerA time-domain reflectometer
85E4A06 -- Which of the following could be determined with a spectrum analyzer? The degree of isolation between the input and output ports of a 2 meter duplexerWhether a crystal is operating on its fundamental or overtone frequencyThe spectral output of a transmitterAll of these choices are correct
86E4A12 -- Which of the following procedures is an important precaution to follow when connecting a spectrum analyzer to a transmitter output?Use high quality double shielded coaxial cables to reduce signal lossesAttenuate the transmitter output going to the spectrum analyzerMatch the antenna to the loadAll of these choices are correct
87E4B10 -- Which of the following describes a method to measure intermodulation distortion in an SSB transmitter?Modulate the transmitter with two non-harmonically related radio frequencies and observe the RF output with a spectrum analyzerModulate the transmitter with two non-harmonically related audio frequencies and observe the RF output with a spectrum analyzerModulate the transmitter with two harmonically related audio frequencies and observe the RF output with a peak reading wattmeterModulate the transmitter with two harmonically related audio frequencies and observe the RF output with a logic analyzer
88Test Equipment Transistor Circuit Parameters Some DC voltage measurements are useful for troubleshooting.VBE ~ 0.7 VDC (Silicon)VBE ~ 0.3 VDC (Germanium)VCE ~ 0.5 x VCC(If class A amplifier.)Other examples in book.
89E4A10 -- Which of the following tests establishes that a silicon NPN junction transistor is biased on?Measure base-to-emitter resistance with an ohmmeter; it should be approximately 6 to 7 ohmsMeasure base-to-emitter resistance with an ohmmeter; it should be approximately 0.6 to 0.7 ohmsMeasure base-to-emitter voltage with a voltmeter; it should be approximately 6 to 7 voltsMeasure base-to-emitter voltage with a voltmeter; it should be approximately 0.6 to 0.7 volts
91Modulation Systems FCC Emission Designations and Terms Specified by ITU.Either 3 or 7 characters.If 3 characters:1st Character - type of modulation of the main carrier.2nd Character - nature of signal(s) modulating the main carrier.3rd Character - type of information to be transmitted.If 7 characters, add 4-character bandwidth designator in front of 3-character designator.
92Modulation Systems FCC Emission Designations and Terms Type of Modulation.NUnmodulated CarrierAAmplitude ModulationRSingle Sideband Reduced CarrierJSingle Sideband Suppressed CarrierCVestigial SidebandFFrequency ModulationGPhase ModulationP, K, L, M, Q, V, W, XVarious Types of Pulse Modulation
93Modulation Systems FCC Emission Designations and Terms Type of Modulating Signal.No modulating signal1A single channel containing quantized or digital information without the use of a modulating sub-carrier2A single channel containing quantized or digital information with the use of a modulating sub-carrier3A single channel containing analogue information7Two or more channels containing quantized or digital information8Two or more channels containing analogue informationXCases not otherwise covered
94Modulation Systems FCC Emission Designations and Terms Type of Transmitted Information.NNo information transmittedATelegraphy - for aural receptionBTelegraphy - for automatic receptionCFacsimileDData transmission, telemetry, telecommandETelephony (including sound broadcasting)FTelevision (video)WCombination of the aboveXCases not otherwise covered
96Modulation 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)PulseData (Packet, PSK-31, etc.)TestImage (SSTV, Fascimile, etc.)
97Modulation 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.
98Modulation Systems FM/PM Modulation and Modulators Deviation ratio. Deviation Ratio = fDev / fModfDev = Maximum frequency deviation.fMod = Maximum modulating frequency.Deviation ratio is constant in both an FM modulator and in a PM modulator.
99Modulation Systems FM/PM Modulation and Modulators Modulation index. Modulation Index = fDev / fmfDev = Maximum frequency deviation.fm = 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)]
100E1B12 -- What is the highest modulation index permitted at the highest modulation frequency for angle modulation?.51.02.03.0
101E8B01 -- 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?FM compressibilityQuieting indexPercentage of modulationModulation index
102E8B02 -- How does the modulation index of a phase-modulated emission vary with RF carrier frequency (the modulated frequency)?It increases as the RF carrier frequency increasesIt decreases as the RF carrier frequency increasesIt varies with the square root of the RF carrier frequencyIt does not depend on the RF carrier frequency
103E8B03 -- 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?30.330001000
104E8B04 -- 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?6000320001/3
105E8B05 -- 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?600.1670.61.67
106E8B06 -- 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?2.140.2140.4747
107E8B09 -- What is meant by deviation ratio? The ratio of the audio modulating frequency to the center carrier frequencyThe ratio of the maximum carrier frequency deviation to the highest audio modulating frequencyThe ratio of the carrier center frequency to the audio modulating frequencyThe ratio of the highest audio modulating frequency to the average audio modulating frequency
108Modulation 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.
109Modulation 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).
110Modulation Systems Pulse Modulation Systems. Pulse amplitude modulation (PAM).Varies amplitude of pulses.
111Modulation Systems Pulse Modulation Systems. Pulse width modulation (PWM).Varies width of pulses.
112Modulation Systems Pulse Modulation Systems. Pulse position modulation (PPM).Varies time at which pulses occur.
113Modulation Systems Pulse Modulation Systems. Pulse code modulation (PCM).Transmits series of binary-coded pulses.
114E8A11 -- What is one use for a pulse modulated signal? Linear amplificationPSK31 data transmissionMultiphase power transmissionDigital data transmission
115E8B07 -- When using a pulse-width modulation system, why is the transmitter's peak power greater than its average power?The signal duty cycle is less than 100%The signal reaches peak amplitude only when voice modulatedThe signal reaches peak amplitude only when voltage spikes are generated within the modulatorThe signal reaches peak amplitude only when the pulses are also amplitude modulated
116E8B08 -- What parameter does the modulating signal vary in a pulse-position modulation system? The number of pulses per secondThe amplitude of the pulsesThe duration of the pulsesThe time at which each pulse occurs
117Modulation Systems Multiplexing. Transmitting multiple, independent signals on one carrier.
118Modulation 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.
119Modulation Systems Multiplexing. Time-division multiplexing. Signals are sampled & samples from each signal are interleaved in sequential time slots.Normally digital transmission.Telemetry.
120E8B10 -- Which of these methods can be used to combine several separate analog information streams into a single analog radio frequency signal?Frequency shift keyingA diversity combinerFrequency division multiplexingPulse compression
121E8B11 -- Which of the following describes frequency division multiplexing? The transmitted signal jumps from band to band at a predetermined rateTwo or more information streams are merged into a "baseband", which then modulates the transmitterThe transmitted signal is divided into packets of informationTwo or more information streams are merged into a digital combiner, which then pulse position modulates the transmitter
122E8B12 -- What is digital time division multiplexing? Two or more data streams are assigned to discrete sub-carriers on an FM transmitterTwo or more signals are arranged to share discrete time slots of a data transmissionTwo or more data streams share the same channel by transmitting time of transmission as the sub-carrierTwo or more signals are quadrature modulated to increase bandwidth efficiency
123Interference and Noise IntermodulationNon-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.
124Interference and Noise Transmitter IntermodulationSignals 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.
125E4D03 -- How can intermodulation interference between two repeaters occur? When the repeaters are in close proximity and the signals cause feedback in the final amplifier of one or both transmittersWhen the repeaters are in close proximity and the signals mix in the final amplifier of one or both transmittersWhen the signals from the transmitters are reflected out of phase from airplanes passing overheadWhen the signals from the transmitters are reflected in phase from airplanes passing overhead
126E4D04 -- Which of the following may reduce or eliminate intermodulation interference in a repeater caused by another transmitter operating in close proximity?A band-pass filter in the feed line between the transmitter and receiverA properly terminated circulator at the output of the transmitterA Class C final amplifierA Class D final amplifier
127E4D06 -- What is the term for unwanted signals generated by the mixing of two or more signals? Amplifier desensitizationNeutralizationAdjacent channel interferenceIntermodulation interference
128E4D07 -- 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 large increase in background noiseA reduction in apparent signal strengthThe desired signal can no longer be heardThe off-frequency unwanted signal is heard in addition to the desired signal
129E4D08 -- What causes intermodulation in an electronic circuit? Too little gainLack of neutralizationNonlinear circuits or devicesPositive feedback
130E4E11 -- 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?The broadcast station is transmitting an over-modulated signalNearby corroded metal joints are mixing and re-radiating the broadcast signalsYou are receiving sky wave signals from a distant stationYour station receiver IF amplifier stage is defective
131Interference and Noise Atmospheric StaticDischarge 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.
132Interference and Noise Atmospheric StaticStatic noise can occur without a thunderstorm.Rain static.Snow static.Wind static.
133E4E06 -- What is a major cause of atmospheric static? Solar radio frequency emissionsThunderstormsGeomagnetic stormsMeteor showers
134Interference and Noise AC Line NoiseMan-made noise caused by electric arc.Electric motors.Light dimmers.Neon signs.Defective doorbell or doorbell transformer.
135Interference and Noise AC Line NoiseInstall “brute force” AC line filter in series with motor power leads.
136E4E05 -- How can noise from an electric motor be suppressed? By installing a high pass filter in series with the motor’s power leadsBy installing a brute-force AC-line filter in series with the motor leadsBy installing a bypass capacitor in series with the motor leadsBy using a ground-fault current interrupter in the circuit used to power the motor
137E4E13 -- What might be the cause of a loud roaring or buzzing AC line interference that comes and goes at intervals?Arcing contacts in a thermostatically controlled deviceA defective doorbell or doorbell transformer inside a nearby residenceA malfunctioning illuminated advertising displayAll of these choices are correct
138Interference and Noise Locating Noise and Interference SourcesInterference from inside building usually conducted through AC power wiring.Inside your house.Outside your house.
139Interference and Noise Locating Noise and Interference SourcesTo 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.
140Interference and Noise Locating Noise and Interference SourcesInterference from outside building usually picked up by antenna or transmission line.Use “fox hunting” techniques to locate source.
141Interference and Noise Locating Noise and Interference SourcesYour 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.
142Interference and Noise Locating Noise and Interference SourcesComputer & 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.
143Interference and Noise Locating Noise and Interference SourcesPlasma TV’s.
144E4E07 -- How can you determine if line noise interference is being generated within your home? By checking the power line voltage with a time domain reflectometerBy observing the AC power line waveform with an oscilloscopeBy turning off the AC power line main circuit breaker and listening on a battery operated radioBy observing the AC power line voltage with a spectrum analyzer
145E4E08 -- What type of signal is picked up by electrical wiring near a radio antenna? A common-mode signal at the frequency of the radio transmitterAn electrical-sparking signalA differential-mode signal at the AC power line frequencyHarmonics of the AC power line frequency
146E4E10 -- What is a common characteristic of interference caused by a touch controlled electrical device?The interfering signal sounds like AC hum on an AM receiver or a carrier modulated by 60 Hz hum on a SSB or CW receiverThe interfering signal may drift slowly across the HF spectrumThe interfering signal can be several kHz in width and usually repeats at regular intervals across a HF bandAll of these choices are correct
147E4E14 -- What is one type of electrical interference that might be caused by the operation of a nearby personal computer?A loud AC hum in the audio output of your station receiverA clicking noise at intervals of a few secondsThe appearance of unstable modulated or unmodulated signals at specific frequenciesA whining type noise that continually pulses off and on
148Interference and Noise Automotive NoiseVehicular System NoiseIgnition system noise.Pre-1975.Resistance spark plugs.High-resistance spark plug cables.Shielded cables.1975 & later.High resistance plugs & cables can degrade engine performance.
149Interference and Noise Automotive NoiseVehicular System NoiseCharging 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.
150Interference and Noise Automotive NoiseVehicular System NoiseInstrument noise.Some instruments can generate RF noise.Install 0.5 μF coaxial capacitor at the sender element.Wiper, fuel pump, & other motors can generate RF noise.Install 0.25 μF capacitor across the motor winding.
151E4E04 -- How can conducted and radiated noise caused by an automobile alternator be suppressed? By installing filter capacitors in series with the DC power lead and by installing a blocking capacitor in the field leadBy installing a noise suppression resistor and a blocking capacitor in both leadsBy installing a high-pass filter in series with the radio's power lead and a low-pass filter in parallel with the field leadBy connecting the radio's power leads directly to the battery and by installing coaxial capacitors in line with the alternator leads
152Interference and Noise Noise ReductionNoise BlankersDetects 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.
153Interference and Noise Noise ReductionDSP 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.
154Interference and Noise Noise ReductionDSP 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.
155E4E01 -- Which of the following types of receiver noise can often be reduced by use of a receiver noise blanker?Ignition noiseBroadband white noiseHeterodyne interferenceAll of these choices are correct
156E4E02 -- Which of the following types of receiver noise can often be reduced with a DSP noise filter?Broadband white noiseIgnition noisePower line noiseAll of these choices are correct
157E4E03 -- Which of the following signals might a receiver noise blanker be able to remove from desired signals?Signals which are constant at all IF levelsSignals which appear across a wide bandwidthSignals which appear at one IF but not anotherSignals which have a sharply peaked frequency distribution
158E4E09 -- What undesirable effect can occur when using an IF noise blanker? Received audio in the speech range might have an echo effectThe audio frequency bandwidth of the received signal might be compressedNearby signals may appear to be excessively wide even if they meet emission standardsFM signals can no longer be demodulated
159E4E12 -- What is one disadvantage of using some types of automatic DSP notch-filters when attempting to copy CW signals?The DSP filter can remove the desired signal at the same time as it removes interfering signalsAny nearby signal passing through the DSP system will overwhelm the desired signalReceived CW signals will appear to be modulated at the DSP clock frequencyRinging in the DSP filter will completely remove the spaces between the CW characters