Presentation on theme: "Amateur Extra License Class"— Presentation transcript:
1 Amateur Extra License Class Chapter 6Electronic Circuits
2 AmplifiersAny circuit that increases the strength of a signal – voltage, current, or power.Input voltages from microvolts to hundreds of volts.Output powers from billionths of a watt to thousands of watts.
3 Amplifiers Definitions. Driver: Circuit that supplies the input signal to the amplifier.Load: Circuit that receives the amplifier’s output signal.Final Amplifier: Last amplifier stage in a transmitter.
4 Amplifiers Amplifier Gain. Ratio of output signal to input signal. Voltage gain = VOUT / VINCurrent gain = IOUT / IINPower gain = POUT / PINCan be expressed as simple ratio.e.g. – Voltage gain = 10Can be expressed in decibels.e.g. – Power gain = 10 dB
5 Amplifiers Input and Output Impedances. Input impedance is load seen by driver.Output Impedance is source impedance.Maximum power transfer occurs when source & load impedances are equal.
6 Amplifiers Discrete Device Amplifiers Common emitter. Most common amplifier type.Provides both voltage gain and current gain.Input & output voltages 180° out of phase.Fairly high input impedance.Output impedance depends on RL.
7 Amplifiers Discrete Device Amplifiers Common emitter. R1 & R2 provide fixed bias.RE provides bias point stability.a.k.a. – Self-bias.Prevents thermal runaway.C2 allows maximum AC signal gain.Emitter bypass.
8 Amplifiers Discrete Device Amplifiers Common base. Provides voltage gain.Current gain < 1.Input & outputvoltages in phase.Low input impedance.High output impedance.
9 Amplifiers Discrete Device Amplifiers Common collector. a.k.a. - Emitter follower.Provides current gain.Voltage gain < 1.Input & output voltages in phase.Fairly high input impedance.Low output impedance.Linear voltage regulator.
10 E7B10 -- In Figure E7-1, what is the purpose of R1 and R2? Load resistorsFixed biasSelf biasFeedback
11 E7B11 -- In Figure E7-1, what is the purpose of R3? Fixed biasEmitter bypassOutput load resistorSelf bias
12 E7B12 -- What type of circuit is shown in Figure E7-1? Switching voltage regulatorLinear voltage regulatorCommon emitter amplifierEmitter follower amplifier
13 E7B13 -- In Figure E7-2, what is the purpose of R? Emitter loadFixed biasCollector loadVoltage regulation
14 E7B14 -- In Figure E7-2, what is the purpose of C2? Output couplingEmitter bypassInput couplingHum filtering
15 E7B15 -- What is one way to prevent thermal runaway in a bipolar transistor amplifier? NeutralizationSelect transistors with high betaUse a resistor in series with the emitterAll of these choices are correct
16 Amplifiers Vacuum Tube Amplifiers Each type of transistor amplifier circuit has a corresponding vacuum tube amplifier circuit.Common-Emitter Common-Cathode.Common-Base Grounded-Grid.Common-Collector Common-Anode.Emitter Follower Cathode Follower.
17 Amplifiers Vacuum Tube Amplifiers. Grounded-Grid Amplifiers. Most common RF power amplifier configuration.Stable.Easier to neutralize.Low input impedance.Little or no input impedance matching required.
18 E7B18 -- Which of the following is a characteristic of a grounded-grid amplifier? High power gainHigh filament voltageLow input impedanceLow bandwidth
19 Amplifiers Op Amp Amplifiers High-gain, direct-coupled, differential amplifier.Differential input Input signal is difference between inverting & non-inverting inputs.Direct-coupled Will amplify DC.Ideal operational amplifierInfinite input impedance.Zero output impedance.Infinite gain.Flat frequency response.Zero offset voltage.0 VIN 0 VOUT
20 Amplifiers Op Amp Amplifiers Circuit characteristics totally determined by external components.In closed-loop configurationInput voltage = 0.Input current = 0.
21 Amplifiers Op Amp Amplifiers Operational amplifier specifications. Open-loop gain.Gain-Bandwidth.Slew rate.Input offset voltage.Input voltage in closed-loop.Input impedance.Output impedance.
22 Amplifiers Op Amp Amplifiers Practical operational amplifier. Differential input.Direct-coupled.Very high input impedance.Very low output impedance.Very high voltage gain.Up to 120 dB.Wide bandwidth.
23 AmplifiersOp Amp AmplifiersInverting Amplifier.Gain = RF / RIN
26 Amplifiers Operational Amplifiers (Op-Amps). Summing Amplifier. Vout = - ((V1 x RF /Rin) + (V2 x RF /Rin) + (V3 x RF /Rin))Vout = - (V1 + V2 + V3) x RF /Rin
27 E7G07 -- What magnitude of voltage gain can be expected from the circuit in Figure E7-4 when R1 is 10 ohms and RF is 470 ohms?0.21944724
28 E7G08 -- How does the gain of an ideal operational amplifier vary with frequency? It increases linearly with increasing frequencyIt decreases linearly with increasing frequencyIt decreases logarithmically with increasing frequencyIt does not vary with frequency
29 E7G09 -- What will be the output voltage of the circuit shown in Figure E7-4 if R1 is 1000 ohms, RF is 10,000 ohms, and 0.23 volts dc is applied to the input?0.23 volts2.3 volts-0.23 volts-2.3 volts
30 E7G10 -- What absolute voltage gain can be expected from the circuit in Figure E7-4 when R1 is 1800 ohms and RF is 68 kilohms?10.033876
31 E7G11 -- What absolute voltage gain can be expected from the circuit in Figure E7-4 when R1 is 3300 ohms and RF is 47 kilohms?281470.07
32 E7G12 -- What is an integrated circuit operational amplifier? A high-gain, direct-coupled differential amplifier with very high input and very low output impedanceA digital audio amplifier whose characteristics are determined by components external to the amplifierAn amplifier used to increase the average output of frequency modulated amateur signals to the legal limitAn RF amplifier used in the UHF and microwave regions
33 E7G13 -- What is meant by the term op-amp input-offset voltage? The output voltage of the op-amp minus its input voltageThe difference between the output voltage of the op-amp and the input voltage required in the immediately following stageThe differential input voltage needed to bring the open-loop output voltage to zeroThe potential between the amplifier input terminals of the op-amp in an open-loop condition
34 E7G14 -- What is the typical input impedance of an integrated circuit op-amp? 100 ohms1000 ohmsVery lowVery high
35 E7G15 -- What is the typical output impedance of an integrated circuit op-amp? Very lowVery high100 ohms1000 ohms
36 Amplifiers Amplifier Classes. Class A Class B On for 360° Best linearity.Least efficient.Class BOn for 180°Non-linear.2 devices in push-pull configuration is linear.More efficient.
37 Amplifiers Amplifier Classes. Class AB Class C On for >180° but < 360°Non-linear.2 devices in push-pull configuration is linear.Compromise between classes A & BClass COn for <180°Highly non-linear.Most efficient.
38 Amplifiers Amplifier Classes. Class D Used for audio amplifiers. Uses switching techniques to achieve high efficiency.Switching speed well above highest frequency to be amplified.Efficiency >90%.
39 E7B01 -- For what portion of a signal cycle does a Class AB amplifier operate? More than 180 degrees but less than 360 degreesExactly 180 degreesThe entire cycleLess than 180 degrees
40 E7B02 -- What is a Class D amplifier? A type of amplifier that uses switching technology to achieve high efficiencyA low power amplifier using a differential amplifier for improved linearityAn amplifier using drift-mode FETs for high efficiencyA frequency doubling amplifier
41 E7B03 -- Which of the following forms the output of a class D amplifier circuit? A low-pass filter to remove switching signal componentsA high-pass filter to compensate for low gain at low frequenciesA matched load resistor to prevent damage by switching transientsA temperature-compensated load resistor to improve linearity
42 E7B04 -- Where on the load line of a Class A common emitter amplifier would bias normally be set? Approximately half-way between saturation and cutoffWhere the load line intersects the voltage axisAt a point where the bias resistor equals the load resistorAt a point where the load line intersects the zero bias current curve
43 Amplifiers Distortion and Intermodulation. Distortion Non-linearity results in distortion.ALL physical components have some non-linearity.Distortion results in harmonics.Can have low distortion or high efficiency, but not both.
44 Amplifiers Distortion and Intermodulation. Intermodulation. 2 or more signals mixing together to produce other frequencies.FIMD = (A x F1) – (B x F2).If A+B is odd, then odd-order intermodulation product.Fimd is near fundamental or odd harmonics of F1 & F2.If A+B is even then even-order intermodulation product.Fimd is near even harmonics of F1 & F2.Since odd-order IMD products are close to desired frequency, spurious signals can be transmitted.
45 Amplifiers Distortion and Intermodulation. Tuned amplifiers. Power amplifiers are a compromise between linearity & efficiency.Tuned output circuit acts like a “flywheel”, minimizing effects of distortion.
46 Amplifiers Distortion and Intermodulation. Selecting amplifier class. For audio, AM or SSB, a linear amplifier is required.For CW or FM, a non-linear amplifier may be used.
47 Amplifiers Distortion and Intermodulation. Selecting amplifier class. For best linearity & lowest efficiency, use Class A.Low-level stages.Audio power amplifiers.For a good compromise between linearity & efficiency, use Class AB.RF Power amplifiers.
48 Amplifiers Distortion and Intermodulation. Selecting amplifier class. For highest efficiency or intentional harmonics, use Class C.Frequency multiplier stages.CW transmitters.FM transmitters & receivers.
49 Amplifiers Distortion and Intermodulation. Selecting amplifier class. Class B push-pull circuits.Audio power amplifiers.Even harmonics are reduced.
50 E7B06 -- Which of the following amplifier types reduces or eliminates even-order harmonics? Push-pushPush-pullClass CClass AB
51 E7B07 -- Which of the following is a likely result when a Class C amplifier is used to amplify a single-sideband phone signal?Reduced intermodulation productsIncreased overall intelligibilitySignal inversionSignal distortion and excessive bandwidth
52 E7B16 -- What is the effect of intermodulation products in a linear power amplifier? Transmission of spurious signalsCreation of parasitic oscillationsLow efficiencyAll of these choices are correct
53 E7B17 -- Why are third-order intermodulation distortion products of particular concern in linear power amplifiers?Because they are relatively close in frequency to the desired signalBecause they are relatively far in frequency from the desired signalBecause they invert the sidebands causing distortionBecause they maintain the sidebands, thus causing multiple duplicate signals
54 Amplifiers Instability and Parasitic Oscillation. Amplifier stability. Excessive gain or undesired positive feedback can cause an amplifier to oscillate.Can occur in any amplifier stage, not just power amplifiers.Can result in:Increased noise figure in receiver.Spurious radiations.Excessive heating.
55 Amplifiers Instability and Parasitic Oscillation. Neutralization. Inter-electrode capacitances in amplifying device and/or stray capacitances in associated circuitry can cause an amplifier to oscillate at the frequency of operation.Oscillation can be prevented by “neutralizing the amplifier.Feed small amount of signal back to input out-of-phase.
56 AmplifiersInstability and Parasitic Oscillation.Neutralization.
57 Amplifiers Instability and Parasitic Oscillation. Not related to operating frequency.Caused by resonances in surrounding circuitry.Typically at VHF or UHF frequencies.Parasitic oscillations in HF vacuum tube amplifiers are eliminated by adding parasitic suppressors to the plate or grid leads.Coil in parallel with resistor.
58 Amplifiers Instability and Parasitic Oscillation. Parasitic suppressor.
59 Amplifiers Instability and Parasitic Oscillation. Parasitic suppressor.
60 E7B05 -- What can be done to prevent unwanted oscillations in an RF power amplifier? Tune the stage for maximum SWRTune both the input and output for maximum powerInstall parasitic suppressors and/or neutralize the stageUse a phase inverter in the output filter
61 E7B08 -- How can an RF power amplifier be neutralized? By increasing the driving powerBy reducing the driving powerBy feeding a 180-degree out-of-phase portion of the output back to the inputBy feeding an in-phase component of the output back to the input
62 Amplifiers VHF, UHF, and Microwave Amplifiers. At VHF & higher frequencies, special techniques & devices are required to design & construct amplifiers.Short wavelengths mean component leads can have significant inductance.Due to internal capacitances, ordinary tubes & transistors lose ability to amplify.The following slides describe only some of the devices & techniques used.
63 Amplifiers VHF, UHF, and Microwave Amplifiers. Klystrons. Velocity modulation.
64 Amplifiers VHF, UHF, and Microwave Amplifiers. Parametric amplifiers. Invented by amateur radio operators.Uses variable reactance (varactor diode) to “pump” input signal.Used for very low noise receive pre-amplifiers at microwave frequencies & above.
65 AmplifiersVHF, UHF, and Microwave Amplifiers.Parametric amplifiers.
66 Amplifiers VHF, UHF, and Microwave Amplifiers. Microwave semiconductor amplifiers.Geometry of junction transistors limits upper frequency limit to a few GHz.Gallium-Arsenide FET’s can operate up to GHz.
67 E7B19 -- What is a klystron?A high speed multivibratorAn electron-coupled oscillator utilizing a pentode vacuum tubeAn oscillator utilizing ceramic elements to achieve stabilityA VHF, UHF, or microwave vacuum tube that uses velocity modulation
68 E7B20 -- What is a parametric amplifier? A type of bipolar operational amplifier with excellent linearity derived from use of very high voltage on the collectorA low-noise VHF or UHF amplifier relying on varying reactance for amplificationA high power amplifier for HF application utilizing the Miller effect to increase gainAn audio push-pull amplifier using silicon carbide transistors for extremely low noise
69 E7B21 -- Which of the following devices is generally best suited for UHF or microwave power amplifier applications?Field effect transistorNuvistorSilicon controlled rectifierTriac
70 Signal Processing Oscillator Circuits & Characteristics. Generates sine wave.Amplifier with positive feedback.AV = Amplifier gain.β = Feedback ratio.Loop Gain = AV x βIf loop gain > 1 and in phase, circuit will oscillate.
72 Signal Processing Oscillator Circuits & Characteristics. Pierce oscillator.Tuned circuit replacedwith a crystal.
73 Signal Processing Oscillator Circuits & Characteristics. Crystals. Usually small wafer of quartz with precise dimensions.Piezoelectric effect.Crystal deforms mechanically when voltage applied.Voltage generated when crystal deformed.
75 Signal Processing Oscillator Circuits & Characteristics. Crystals. Frequency is accurate when connected to a specified parallel capacitance.
76 Signal Processing Oscillator Circuits & Characteristics. Variable-frequency oscillator.Make either L or C adjustable.Not as stable.
77 Signal Processing Oscillator Circuits & Characteristics. Microwave oscillators.Magnetron.Diode tube with a resonant cavity surrounded by external magnet.Magnetic field causes electrons to spiral, generating RF energy at a frequency determined by the dimensions of the cavity.
78 Signal Processing Oscillator Circuits & Characteristics. Microwave oscillators.Gunn diode oscillators.Diode.Similar to tunnel diode.Negative resistance.Resonant cavity
79 E6E03 -- What is one aspect of the piezoelectric effect? Physical deformation of a crystal by the application of a voltageMechanical deformation of a crystal by the application of a magnetic fieldThe generation of electrical energy by the application of lightReversed conduction states when a P-N junction is exposed to light
80 E6E09 -- Which of the following must be done to insure that a crystal oscillator provides the frequency specified by the crystal manufacturer?Provide the crystal with a specified parallel inductanceProvide the crystal with a specified parallel capacitanceBias the crystal at a specified voltageBias the crystal at a specified current
81 E7H01 -- What are three oscillator circuits used in Amateur Radio equipment? Taft, Pierce and negative feedbackPierce, Fenner and BeaneTaft, Hartley and PierceColpitts, Hartley and Pierce
82 E7H02 -- What condition must exist for a circuit to oscillate? It must have at least two stagesIt must be neutralizedIt must have positive feedback with a gain greater than 1It must have negative feedback sufficient to cancel the input signal
83 E7H03 -- How is positive feedback supplied in a Hartley oscillator? Through a tapped coilThrough a capacitive dividerThrough link couplingThrough a neutralizing capacitor
84 E7H04 -- How is positive feedback supplied in a Colpitts oscillator? Through a tapped coilThrough link couplingThrough a capacitive dividerThrough a neutralizing capacitor
85 E7H05 -- How is positive feedback supplied in a Pierce oscillator? Through a tapped coilThrough link couplingThrough a neutralizing capacitorThrough a quartz crystal
86 E7H06 -- Which of the following oscillator circuits are commonly used in VFOs? Pierce and ZenerColpitts and HartleyArmstrong and deForestNegative feedback and balanced feedback
87 E7H07 -- What is a magnetron oscillator? An oscillator in which the output is fed back to the input by the magnetic field of a transformerA crystal oscillator in which variable frequency is obtained by placing the crystal in a strong magnetic fieldA UHF or microwave oscillator consisting of a diode vacuum tube with a specially shaped anode, surrounded by an external magnetA reference standard oscillator in which the oscillations are synchronized by magnetic coupling to a rubidium gas tube
88 E7H08 -- What is a Gunn diode oscillator? An oscillator based on the negative resistance properties of properly-doped semiconductorsAn oscillator based on the argon gas diodeA highly stable reference oscillator based on the tee-notch principleA highly stable reference oscillator based on the hot-carrier effect
89 Signal Processing Digital Signal Processing (DSP) Part of practically all modern transceivers.Allows signal processing difficult to obtain by analog methods.Procedure:Convert analog signal to series of numbers.Process series of numbers mathematically.Convert resulting series of numbers back to analog signal.
90 Signal Processing Digital Signal Processing (DSP) Analog-to-digital conversion.Sequential sampling.Sample signal at regular intervals (sequential sampling).Convert signal value to a number.Higher sampling rates yields higher accuracy.More “bits” in the number yields higher accuracy
91 Signal Processing Digital Signal Processing (DSP) Sine wave, alias sine wave, harmonic sampling.If sample rate is less than frequency of signal being sampled, result does not match input signal.Retains general shape of sine wave but at lower frequency.Downward frequency translation can be useful.Longer time between samples provides more processing time.
92 Signal Processing Digital Signal Processing (DSP) Sine wave, alias sine wave, harmonic sampling.Harmonic sampling.If frequency of signal being sampled is about twice the sampling rate, result is exactly same as if frequency is equal to sampling rate.Must limit bandwidth of signal being sampled.
93 Signal Processing Digital Signal Processing (DSP) Sine wave, alias sine wave, harmonic sampling.Aliasing.Nyquist sampling theorem.To avoid aliasing, sampling rate must be ≥ 2x highest frequency being sampled.
94 Signal Processing Digital Signal Processing (DSP) Data converters. Analog-to-digital converter (ADC).Device that performs analog-to-digital conversion.Produces a binary number that is directly proportional to value of the input voltage.More bits in binary number higher resolution.8 bits 256 steps.16 bits 65,536 steps.24 bits 16,777,216 steps.
95 Signal Processing Digital Signal Processing (DSP) Data converters. Digital-to-analog converter (DAC).Device that performs digital-to-analog conversion.Produces an output voltage that is directly proportional to value of a binary number.More bits in binary number higher resolution.8 bits 256 steps.16 bits 65,536 steps.24 bits 16,777,216 steps.
96 Signal Processing Digital Signal Processing (DSP) Representation of Numbers.Floating PointSimilar to scientific notation.Greater range of numbers can be handled.Not necessary for DSP since range of numbers limited by precision of ADC.Used in PC’s.Fixed PointFraction <1.Used for most DSP in amateur equipment.
97 Signal Processing Digital Signal Processing (DSP) Software-Defined Radio (SDR).A software-defined radio (SDR) system is a radio communication system where components that have been typically implemented in hardware (e.g. mixers, filters, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a computer or embedded computing devices.
98 Signal Processing Digital Signal Processing (DSP) Software-Defined Radio (SDR).The ideal SDR receiver would be to attach an antenna to an analog-to-digital converter (ADC).Similarly, the ideal SDR transmitter would be to attach a digital-to-analog converter (DAC) to an antenna.Not feasible with current technology, so some compromise is necessary.
99 Signal Processing Digital Signal Processing (DSP) Software-Defined Radio (SDR).Some analog processing still required.Future is an all-digital radio.Commercial SDR’s now available for amateur use.
100 E8A14 -- Which of these methods is commonly used to convert analog signals to digital signals? Sequential samplingHarmonic regenerationLevel shiftingPhase reversal
101 Signal Processing Mixers Used to change the frequency of a signal. Mathematically multiplies 2 frequencies together, generating 4 output frequencies.f1 x f2 f1, f2, f1+f2, f1–f2Superheterodyne receiver.fRF x fLO fLO–fRF
102 Signal Processing Mixers Only enough pre-amp gain should be used to overcome mixer losses.Excessive input signal can:Overload mixer circuit.Distort signal.Generate spurious mixer products.Operation of a mixer is similar to operation of product detectors & modulators.
106 Signal Processing Mixers Double-balanced mixer. fRF & fLO are suppressed leaving only sum & difference frequencies.
107 Signal Processing Mixers Active mixers. Uses active components such as transistors or FET’s.Amplification possible.No conversion loss.Less LO signal needed.Generate less noise.Strong signal handling capability not as good as passive mixers.
108 Signal ProcessingMixersDual-gate MOSFET mixer.
109 E7E08 -- What are the principal frequencies that appear at the output of a mixer circuit? Two and four times the original frequencyThe sum, difference and square root of the input frequenciesThe two input frequencies along with their sum and difference frequencies1.414 and times the input frequency
110 E7E09 -- What occurs when an excessive amount of signal energy reaches a mixer circuit? Spurious mixer products are generatedMixer blanking occursAutomatic limiting occursA beat frequency is generated
111 Signal Processing Modulation Combining a modulating signal with an RF signal resulting in a signal that can be transmitted.Modulating signal also known as the “baseband” signal.
112 Signal Processing Modulators Amplitude modulation. Multiplying (mixing) AF signal & carrier produces amplitude modulated signal.
113 Signal Processing Modulators Single-sideband modulation. Filter method.Start with AM double-sideband signal & use filters to remove one sideband & the carrier.Better idea – use a balanced modulator (mixer) to generate a double-sideband suppressed carrier signal. Then all you have to filter out is the unwanted sideband.
114 Signal Processing Modulators Single-sideband modulation. Phasing (quadrature) method.Generate 2 identical carrier signals, 90° out of phase.Generate 2 identical audio signals, 90° out of phase.Mix these together in a pair of balanced modulators & result is that the carrier & one sideband are canceled out leaving only one sideband.90° phase shift of band of audio frequencies difficult to accomplish in hardware, but easy in software.Hilbert-transform filters.Most SDR transmitters use the phasing or quadrature method to generate SSB mathematically.
115 Signal Processing Modulators Single-sideband modulation. Phasing (quadrature) method.
116 E7C09 -- What type of digital signal processing filter might be used to generate an SSB signal? An adaptive filterA notch filterA Hilbert-transform filterAn elliptical filter
117 E7E04 -- What is one way a single-sideband phone signal can be generated? By using a balanced modulator followed by a filterBy using a reactance modulator followed by a mixerBy using a loop modulator followed by a mixerBy driving a product detector with a DSB signal
118 E7E07 -- What is meant by the term baseband in radio communications? The lowest frequency band that the transmitter or receiver coversThe frequency components present in the modulating signalThe unmodulated bandwidth of the transmitted signalThe basic oscillator frequency in an FM transmitter that is multiplied to increase the deviation and carrier frequency
119 E7E13 -- Which of the following describes a common means of generating an SSB signal when using digital signal processing?Mixing products are converted to voltages and subtracted by adder circuitsA frequency synthesizer removes the unwanted sidebandsEmulation of quartz crystal filter characteristicsThe quadrature method
121 Signal Processing Modulators Frequency and phase modulation. Direct FM Frequency deviation constant withmodulating frequency.Generated by adding reactancemodulator to oscillator circuit.
122 Signal Processing Modulators Frequency and phase modulation. Indirect FM (phase modulation).Frequency deviation increases with increasing modulating frequency.Generated by adding reactance modulator to any stage other than the oscillator.
123 Signal Processing Modulators Frequency and phase modulation. Pre-emphasis is amplifying the higher modulating frequencies more than the lower frequencies.Adding pre-emphasis to the modulating signal of an FM transmitter yields a PM signal.Pre-emphasis yields a better signal-to-noise ratio.Corresponding de-emphasis is added to the receiver.
124 E7E01 -- Which of the following can be used to generate FM phone emissions? A balanced modulator on the audio amplifierA reactance modulator on the oscillatorA reactance modulator on the final amplifierA balanced modulator on the oscillator
125 E7E02 -- What is the function of a reactance modulator? To produce PM signals by using an electrically variable resistanceTo produce AM signals by using an electrically variable inductance or capacitanceTo produce AM signals by using an electrically variable resistanceTo produce PM signals by using an electrically variable inductance or capacitance
126 E7E03 -- How does an analog phase modulator function? By varying the tuning of a microphone preamplifier to produce PM signalsBy varying the tuning of an amplifier tank circuit to produce AM signalsBy varying the tuning of an amplifier tank circuit to produce PM signalsBy varying the tuning of a microphone preamplifier to produce AM signals
127 E7E05 -- What circuit is added to an FM transmitter to boost the higher audio frequencies? A de-emphasis networkA heterodyne suppressorAn audio prescalerA pre-emphasis network
128 E7E06 -- Why is de-emphasis commonly used in FM communications receivers? For compatibility with transmitters using phase modulationTo reduce impulse noise receptionFor higher efficiencyTo remove third-order distortion products
129 Signal Processing Detectors and Demodulators Detectors. Simplest detector is the diode detector.a.k.a. – Envelope detector.
130 Signal Processing Detectors and Demodulators Product Detectors. Multiplies signal with a local oscillator to retrieve the modulating signal.fRF x fLO fRF–fLO fAF
131 Signal Processing Detectors and Demodulators Product Detectors. For AM, local oscillator frequency & phase must precisely match AM signal carrier.For SSB, local oscillator frequency must match carrier frequency of suppressed carrier.For CW, local oscillator frequency is offset from signal frequency to produce a sidetone.
132 Signal Processing Detectors and Demodulators Direct Conversion. Local oscillator is at the frequency of the received signal.Requires very stable local oscillator.Software-defined radios (SDR) typically uses a modified direct-conversion technique.Signal is converted to a baseband AF signal for A-to-D conversion & processing.
133 Signal Processing Detectors and Demodulators Detecting FM signals. Frequency discriminator.a.k.a. – Foster-Seeley Detector.
134 Signal Processing Detectors and Demodulators Detecting FM signals. Ratio detector.
135 Signal Processing Detectors and Demodulators Detecting FM signals. Slope detector.Use AM receiver’s selectivity curve to detect FM.
136 E7E10 -- How does a diode detector function? By rectification and filtering of RF signalsBy breakdown of the Zener voltageBy mixing signals with noise in the transition region of the diodeBy sensing the change of reactance in the diode with respect to frequency
137 E7E11 -- Which of the following types of detector is well suited for demodulating SSB signals? DiscriminatorPhase detectorProduct detectorPhase comparator
138 E7E12 -- What is a frequency discriminator stage in a FM receiver? An FM generator circuitA circuit for filtering two closely adjacent signalsAn automatic band-switching circuitA circuit for detecting FM signals
139 E7E14 -- What is meant by direct conversion when referring to a software defined receiver? Software is converted from source code to object code during operation of the receiverIncoming RF is converted to the IF frequency by rectification to generate the control voltage for a voltage controlled oscillatorIncoming RF is mixed to “baseband” for analog-to-digital conversion and subsequent processingSoftware is generated in machine language, avoiding the need for compilers
140 Signal ProcessingFrequency SynthesisPhase-Locked Loop (PLL).
141 Signal Processing Frequency Synthesis Phase-Locked Loop (PLL). Servo loopError-detecting circuit with negative feedback.Allows VFO to have stability of crystal oscillator.Can do FM modulation & demodulation.Capture range – Range of frequencies over which PLL can achieve lock.Spectral impurities are mainly broadband phase noise.PLL has been replaced in modern designs by direct digital synthesis.
142 Signal Processing Frequency Synthesis Direct Digital Synthesis (DDS). Generates sine wave by looking up values in a table.Changing phase increment changes frequency.Increase tuning range by adding PLL.No phase noise, but spurs at discrete frequencies.
143 E7H09 -- What type of frequency synthesizer circuit uses a phase accumulator, lookup table, digital to analog converter and a low-pass anti-alias filter?A direct digital synthesizerA hybrid synthesizerA phase locked loop synthesizerA diode-switching matrix synthesizer
144 E7H10 -- What information is contained in the lookup table of a direct digital frequency synthesizer?The phase relationship between a reference oscillator and the output waveformThe amplitude values that represent a sine-wave outputThe phase relationship between a voltage-controlled oscillator and the output waveformThe synthesizer frequency limits and frequency values stored in the radio memories
145 E7H11 -- What are the major spectral impurity components of direct digital synthesizers? Broadband noiseDigital conversion noiseSpurious signals at discrete frequenciesNyquist limit noise
146 E7H12 -- Which of the following is a principal component of a direct digital synthesizer (DDS)? Phase splitterHex inverterChroma demodulatorPhase accumulator
147 E7H13 -- What is the capture range of a phase-locked loop circuit? The frequency range over which the circuit can lockThe voltage range over which the circuit can lockThe input impedance range over which the circuit can lockThe range of time it takes the circuit to lock
148 E7H14 -- What is a phase-locked loop circuit? An electronic servo loop consisting of a ratio detector, reactance modulator, and voltage-controlled oscillatorAn electronic circuit also known as a monostable multivibratorAn electronic servo loop consisting of a phase detector, a low-pass filter, a voltage-controlled oscillator, and a stable reference oscillatorAn electronic circuit consisting of a precision push-pull amplifier with a differential input
149 E7H15 -- Which of these functions can be performed by a phase-locked loop? Wide-band AF and RF power amplificationComparison of two digital input signals, digital pulse counterPhotovoltaic conversion, optical couplingFrequency synthesis, FM demodulation
150 E7H16 -- Why is the short-term stability of the reference oscillator important in the design of a phase locked loop (PLL) frequency synthesizer?Any amplitude variations in the reference oscillator signal will prevent the loop from locking to the desired signalAny phase variations in the reference oscillator signal will produce phase noise in the synthesizer outputAny phase variations in the reference oscillator signal will produce harmonic distortion in the modulating signalAny amplitude variations in the reference oscillator signal will prevent the loop from changing frequency
151 E7H17 -- Why is a phase-locked loop often used as part of a variable frequency synthesizer for receivers and transmitters?It generates FM sidebandsIt eliminates the need for a voltage controlled oscillatorIt makes it possible for a VFO to have the same degree of frequency stability as a crystal oscillatorIt can be used to generate or demodulate SSB signals by quadrature phase synchronization
152 E7H18 -- What are the major spectral impurity components of phase-locked loop synthesizers? Phase noiseDigital conversion noiseSpurious signals at discrete frequenciesNyquist limit noise
153 Filters and Impedance Matching Filter Families and Response TypesFilters are circuits designed to pass certain frequencies and reject others.R-C circuits.R-L circuits.R-L-C circuits.A resonant circuit is a simple filter.Filters normally pass a wider range of frequencies than a simple resonant circuit.
154 Filters and Impedance Matching Filter Families and Response TypesPassive filters.Constructed using only passive components.Capacitors.Inductors.Resistors.Other types.Crystal.Mechanical.Cavity.Always have insertion loss.
155 Filters and Impedance Matching Filter Families and Response TypesActive filters.Include an amplifying device.No insertion loss.Can have gain.Some types of filters can ONLY be built using active components.
156 Filters and Impedance Matching Filter ClassificationLow-pass filter.Passes all frequencies below the cut-off frequency.Attenuates all frequencies above the cut-off frequency.Cut-off frequency is the frequency where the response falls to 3 dB below the maximum level.
157 Filters and Impedance Matching Filter ClassificationHigh-pass filter.Attenuates all frequencies below the cut-off frequency.Passes all frequencies above the cut-off frequency.Cut-off frequency is the frequency where the response rises to 3 dB below the maximum level.
158 Filters and Impedance Matching Filter ClassificationBand-pass filter.2 cut-off frequencies.Cut-off frequencies are frequencies where response is 3dB below maximum.Passes all frequencies between the cut-off frequencies.Attenuates all frequencies outside of the cut-off frequencies.
159 Filters and Impedance Matching Filter ClassificationBand-reject filter.If the passband is narrow, it is called a notch filter.2 cut-off frequencies.Attenuates all frequencies between the cut-off frequencies.Passes all frequenciesoutside of the cut-offfrequencies.
160 Filters and Impedance Matching Filter DesignDefinitions.Response curve.Output signal level vs. frequency.Cut-off frequency = -3 dB point.Cut-off transition.Steepness of curve in transistion region.Steep transition curve sharp filter.Ripple.Variations of response curve in passband or outside of passband.
161 Filters and Impedance Matching Filter DesignDefinitions.Phase response.Shift of signal phase vs. frequency.Higher attenuation more phase shift.Linear phase shift means phase shift is smooth with no ripple as frequency changes.Non-linear phase response can distort digital signals.Ringing.Oscillations continue after signal is removed.
162 Filters and Impedance Matching Filter DesignButterworthMinimum ripple in both pass band & stop band.Cutoff transition smooth but not steep.Smoothly varying phase response.
163 Filters and Impedance Matching Filter DesignChebyshevRipple in pass band.Sharper cutoff transition.Significant phase shift in pass band.
164 Filters and Impedance Matching Filter DesignEllipticalRipple in both pass band & stop band.Sharpest cutoff transition.Notches are positioned at specific frequencies in stopband to make transition as sharp as possible.
165 Filters and Impedance Matching Filter DesignShape factor.Measurement of “sharpness” of filter.Ratio of -60dB bandwidth to -6dB bandwidth.SF = BW60dB / BW6dBThe closer the ratio is to 1.0, the sharper the filter.An ideal filter would have a shape factor of 1.0.
168 Filters and Impedance Matching Cavity FiltersCavity filters use the resonant properties of a conductive tube or box to act as a filter.Cavity filters have an extremely narrow bandwidth (extremely high Q) and very low loss.Cavity filters are often used in repeater duplexers.
169 E7C05 -- Which filter type is described as having ripple in the passband and a sharp cutoff? A Butterworth filterAn active LC filterA passive op-amp filterA Chebyshev filter
170 E7C06 -- What are the distinguishing features of an elliptical filter? Gradual passband rolloff with minimal stop band rippleExtremely flat response over its pass band with gradually rounded stop band cornersExtremely sharp cutoff with one or more notches in the stop bandGradual passband rolloff with extreme stop band ripple
171 E7C07 -- What kind of filter would you use to attenuate an interfering carrier signal while receiving an SSB transmission?A band-pass filterA notch filterA Pi-network filterAn all-pass filter
172 E7C10 -- Which of the following filters would be the best choice for use in a 2 meter repeater duplexer?A crystal filterA cavity filterA DSP filterAn L-C filter
173 E7C14 -- Which of these modes is most affected by non-linear phase response in a receiver IF filter? Meteor ScatterSingle-Sideband voiceDigitalVideo
174 E7G02 -- What is the effect of ringing in a filter? An echo caused by a long time delayA reduction in high frequency responsePartial cancellation of the signal over a range of frequenciesUndesired oscillations added to the desired signal
175 Filters and Impedance Matching Crystal filters.IF stages of a receiver require very narrow bandwidth (high Q) filters with sharp transitions to filter out adjacent signals.Cannot be achieved with L-C filters.SSB transmitters require very narrow bandwidth (high Q) filters with sharp transitions to filter out unwanted sideband.
176 Filters and Impedance Matching Crystal filters.Lattice filter.Typically used in SSB transmitters to remove unwanted sideband.
177 Filters and Impedance Matching Crystal filters.Ladder filter.Bandwidth & response determined by frequencies of individual crystals.
178 Filters and Impedance Matching Crystal filters.Jones filter.Variable-bandwidth crystal ladder filter.Invented by Lee J. Jones, WB4JTR, of Ten-Tec.
179 Filters and Impedance Matching Crystal filters.Jones filter.NOTE: The question pool (E6E12) mistakenly refers to the Jones filter as a crystal lattice filter when in fact, it is a crystal ladder filter.
180 E6E01 -- What is a crystal lattice filter? A power supply filter made with interlaced quartz crystalsAn audio filter made with four quartz crystals that resonate at 1-kHz intervalsA filter with wide bandwidth and shallow skirts made using quartz crystalsA filter with narrow bandwidth and steep skirts made using quartz crystals
181 E6E02 -- Which of the following factors has the greatest effect in helping determine the bandwidth and response shape of a crystal ladder filter?The relative frequencies of the individual crystalsThe DC voltage applied to the quartz crystalThe gain of the RF stage preceding the filterThe amplitude of the signals passing through the filter
182 An automatic notch filter A variable bandwidth crystal lattice filter E6E12 -- What is a "Jones filter" as used as part of a HF receiver IF stage?An automatic notch filterA variable bandwidth crystal lattice filterA special filter that emphasizes image responsesA filter that removes impulse noise
183 Filters and Impedance Matching Active filters.Active audio filtersCan be built without inductors.Smaller & lighter.No insertion loss & can have gain.Op-amps.Filter characteristics determined by external components.Ringing can result if gain and/or Q are too high.Best suited for audio filtering in receivers.
184 Filters and Impedance Matching Active filters.Active audio filters.An active band-pass filter.
185 Filters and Impedance Matching Active filters.Active audio filtersPick standard value capacitors.Low-loss.Temperature stable.Polystyrene (?).Calculate resistors.
186 E7G01 -- What primarily determines the gain and frequency characteristics of an op-amp RC active filter?The values of capacitors and resistors built into the op-ampThe values of capacitors and resistors external to the op-ampThe input voltage and frequency of the op-amp's DC power supplyThe output voltage and smoothness of the op-amp's DC power supply
187 E7G03 -- Which of the following is an advantage of using an op-amp instead of LC elements in an audio filter?Op-amps are more ruggedOp-amps are fixed at one frequencyOp-amps are available in more varieties than are LC elementsOp-amps exhibit gain rather than insertion loss
188 E7G04 -- Which of the following is a type of capacitor best suited for use in high-stability op-amp RC active filter circuits?ElectrolyticDisc ceramicPolystyrenePaper
189 E7G05 -- How can unwanted ringing and audio instability be prevented in a multi-section op-amp RC audio filter circuit?Restrict both gain and QRestrict gain, but increase QRestrict Q, but increase gainIncrease both gain and Q
190 E7G06 -- Which of the following is the most appropriate use of an op-amp active filter? As a high-pass filter used to block RFI at the input to receiversAs a low-pass filter used between a transmitter and a transmission lineFor smoothing power-supply outputAs an audio filter in a receiver
191 Filters and Impedance Matching Digital Signal Processing (DSP) Filters.No tuning required.No worry about selecting standard component values.Adaptive processing.Software can recognize & adapt to different signals & conditions.
192 Filters and Impedance Matching Digital Signal Processing (DSP) Filters.Can build filters impossible to achieve with hardware.“Brick wall” filters approach shape factors of 1.0.Filter Characteristics6dB Bandwidth 2587 Hz,60dB Bandwidth 2756 HzShape Factor ~1.06
193 E7C08 -- What kind of digital signal processing audio filter might be used to remove unwanted noise from a received SSB signal?An adaptive filterA crystal-lattice filterA Hilbert-transform filterA phase-inverting filter
194 Filters and Impedance Matching If load & source impedances are not equal, an impedance matching network is needed for maximum power transfer.Assuming a source impedance of 50Ω, the matching network must:Cancel the reactive portion of the load impedance.Transform the resistive component to 50Ω.
195 Filters and Impedance Matching L Networks.Can match virtually any 2 impedances.Q is fixed.Usually only designed to work on a single band.Which variation to use depends on ratio of impedances to be matched.
196 Filters and Impedance Matching Pi-Networks.Equivalent to 2 L-networks connected back-to-back.Matches wide range of load impedances.Q can be varied depending on component values chosen.Used in most modern tube amplifiers.
197 Filters and Impedance Matching Pi-Networks.Adjust CTune for minimum plate current.Adjust CLoad for maximum permissible plate current.Repeat.
198 Filters and Impedance Matching Pi-L networks.More harmonic reduction.
199 Filters and Impedance Matching T-Networks.High-pass filter.Can match wide range of impedances.Lower loss than pi-network.Used in most antenna tuners.
200 E7B09 -- Which of the following describes how the loading and tuning capacitors are to be adjusted when tuning a vacuum tube RF power amplifier that employs a pi-network output circuit?The loading capacitor is set to maximum capacitance and the tuning capacitor is adjusted for minimum allowable plate currentThe tuning capacitor is set to maximum capacitance and the loading capacitor is adjusted for minimum plate permissible currentThe loading capacitor is adjusted to minimum plate current while alternately adjusting the tuning capacitor for maximum allowable plate currentThe tuning capacitor is adjusted for minimum plate current, while the loading capacitor is adjusted for maximum permissible plate current
201 E7C01 -- How are the capacitors and inductors of a low-pass filter Pi-network arranged between the network's input and output?Two inductors are in series between the input and output, and a capacitor is connected between the two inductors and groundTwo capacitors are in series between the input and output and an inductor is connected between the two capacitors and groundAn inductor is connected between the input and ground, another inductor is connected between the output and ground, and a capacitor is connected between the input and outputA capacitor is connected between the input and ground, another capacitor is connected between the output and ground, and an inductor is connected between input and output
202 E7C02 -- A T-network with series capacitors and a parallel shunt inductor has which of the following properties?It is a low-pass filterIt is a band-pass filterIt is a high-pass filterIt is a notch filter
203 E7C03 -- What advantage does a Pi-L-network have over a Pi-network for impedance matching between the final amplifier of a vacuum-tube transmitter and an antenna?Greater harmonic suppressionHigher efficiencyLower lossesGreater transformation range
204 E7C04 -- How does an impedance-matching circuit transform a complex impedance to a resistive impedance?It introduces negative resistance to cancel the resistive part of impedanceIt introduces transconductance to cancel the reactive part of impedanceIt cancels the reactive part of the impedance and changes the resistive part to a desired valueNetwork resistances are substituted for load resistances and reactances are matched to the resistances
205 E7C11 -- Which of the following is the common name for a filter network which is equivalent to two L networks connected back-to-back with the inductors in series and the capacitors in shunt at the input and output?Pi-LCascodeOmegaPi
206 E7C12 -- Which of the following describes a Pi-L network used for matching a vacuum-tube final amplifier to a 50-ohm unbalanced output?A Phase Inverter Load networkA Pi network with an additional series inductor on the outputA network with only three discrete partsA matching network in which all components are isolated from ground
207 E7C13 -- What is one advantage of a Pi matching network over an L matching network consisting of a single inductor and a single capacitor?The Q of Pi networks can be varied depending on the component values chosenL networks can not perform impedance transformationPi networks have fewer componentsPi networks are designed for balanced input and output
208 Power Supplies Linear Voltage Regulators. Shunt Regulators. Lousy efficiency.Constant current drawn from source.Maximum current flows all the time.Series Regulators.Good efficiency.Only the current required by the load flows.
209 Power Supplies Linear Voltage Regulators. Basic series regulator circuit.C1 -- Input by-pass capacitor.Filters supply voltage.C2 – Hum-filter capacitor.Bypasses hum around D1.C3 – Output by-pass capacitor.Often 2 capacitors in parallel.Large value capacitor to filter output.Small value capacitor to preventself-oscillation.
210 Power Supplies Linear Voltage Regulators. Basic series regulator circuit.D1 – Zener diode.Provides voltage reference.Q1 – Series pass transistor.Increases current handling capability of regulator.
211 Power Supplies Linear Voltage Regulators. Basic series regulator circuit.R1 – Bias resistor.Provides bias current to D1 & Q1.R2 – Load resistor.Provides minimum load current for Q1
212 Power Supplies Linear Voltage Regulators. IC “3-Terminal” Regulators. Thermal shutdown.Overvoltage protection.Foldback current limiting.LM78Lxx mA.LM78xx -- 1 Amp.LM78Hxx -- 3 Amps.
213 Power Supplies Linear Voltage Regulators. Efficiency. Both shunt & series regulators dissipate a significant amount of power as heat.Series regulators are more efficient because only current required by the load is drawn.Efficiency = 100% x POut / PIn
214 E7D01 -- What is one characteristic of a linear electronic voltage regulator? It has a ramp voltage as its outputIt eliminates the need for a pass transistorThe control element duty cycle is proportional to the line or load conditionsThe conduction of a control element is varied to maintain a constant output voltage
215 E7D03 -- What device is typically used as a stable reference voltage in a linear voltage regulator? A Zener diodeA tunnel diodeAn SCRA varactor diode
216 E7D04 -- Which of the following types of linear voltage regulator usually make the most efficient use of the primary power source?A series current sourceA series regulatorA shunt regulatorA shunt current source
217 E7D05 -- Which of the following types of linear voltage regulator places a constant load on the unregulated voltage source?A constant current sourceA series regulatorA shunt current sourceA shunt regulator
218 E7D06 -- What is the purpose of Q1 in the circuit shown in Figure E7-3? It provides negative feedback to improve regulationIt provides a constant load for the voltage sourceIt increases the current-handling capability of the regulatorIt provides D1 with current
219 E7D07 -- What is the purpose of C2 in the circuit shown in Figure E7-3? A. It bypasses hum around D1B. It is a brute force filter for the outputC. To self-resonate at the hum frequencyD. To provide fixed DC bias for Q1
220 E7D08 -- What type of circuit is shown in Figure E7-3? Switching voltage regulatorGrounded emitter amplifierLinear voltage regulatorEmitter follower
221 E7D09 -- What is the purpose of C1 in the circuit shown in Figure E7-3? It resonates at the ripple frequencyIt provides fixed bias for Q1It decouples the outputIt filters the supply voltage
222 E7D10 -- What is the purpose of C3 in the circuit shown in Figure E7-3? It prevents self-oscillationIt provides brute force filtering of the outputIt provides fixed bias for Q1It clips the peaks of the ripple
223 E7D11 -- What is the purpose of R1 in the circuit shown in Figure E7-3? It provides a constant load to the voltage sourceIt couples hum to D1It supplies current to D1It bypasses hum around D1
224 E7D12 -- What is the purpose of R2 in the circuit shown in Figure E7-3? It provides fixed bias for Q1It provides fixed bias for D1It decouples hum from D1It provides a constant minimum load for Q1
225 E7D13 -- What is the purpose of D1 in the circuit shown in Figure E7-3? To provide line voltage stabilizationTo provide a voltage referencePeak clippingHum filtering
226 Power Supplies Switching Regulators AC input is rectified & switched on/off at a high frequency.Pulse width is varied to maintain constant average voltage.A transformer changes the voltage level.Output from transformer is rectified & filtered.Output is sampled & compared to a reference.Difference is used to control the pulse width.
228 Power Supplies Switching Regulators More efficient than linear regulators.Regulation accomplished by varying duty-cycle of input power rather than by dissipating excess power as heat.Smaller, lighter, & less expensive than linear regulators.High switching rate allows use of smaller transformers & filter components.
229 E7D02 -- What is one characteristic of a switching electronic voltage regulator? The resistance of a control element is varied in direct proportion to the line voltage or load currentIt is generally less efficient than a linear regulatorThe control device’s duty cycle is controlled to produce a constant average output voltageIt gives a ramp voltage at its output
230 E7D17 -- What is the primary reason that a high-frequency inverter type high-voltage power supply can be both less expensive and lighter in weight than a conventional power supply?The inverter design does not require any output filteringIt uses a diode bridge rectifier for increased outputThe high frequency inverter design uses much smaller transformers and filter components for an equivalent power outputIt uses a large power-factor compensation capacitor to create "free power” from the unused portion of the AC cycle
231 Power Supplies High Voltage Techniques. Bleeder resistor. Discharges capacitors when power is turned off.Improves voltage regulation by providing a minimum load current.Voltage equalizing resistors.Equalizes voltages across filter capacitors in series.
232 Power Supplies High Voltage Techniques. Step-start. Resistor in series with transformer primary.Relay shorts resistor after specified time.Limits in-rush current.Reduces stress on rectifiers & filter capacitors by limiting in-rush current.Capacitors charge more slowly.
233 E7D14 -- What is one purpose of a "bleeder" resistor in a conventional (unregulated) power supply? To cut down on waste heat generated by the power supplyTo balance the low-voltage filament windingsTo improve output voltage regulationTo boost the amount of output current
234 E7D15 -- What is the purpose of a "step-start" circuit in a high-voltage power supply? To provide a dual-voltage output for reduced power applicationsTo compensate for variations of the incoming line voltageTo allow for remote control of the power supplyTo allow the filter capacitors to charge gradually
235 E7D16 -- When several electrolytic filter capacitors are connected in series to increase the operating voltage of a power supply filter circuit, why should resistors be connected across each capacitor?To equalize, as much as possible, the voltage drop across each capacitorTo provide a safety bleeder to discharge the capacitors when the supply is offTo provide a minimum load current to reduce voltage excursions at light loadsAll of these choices are correct
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