US_EXTRA
Amateur Extra - Practical circuits and system design
Practical circuits and system design groups the E7 section questions for focused review and easier weak-point tracking.
99
Questions
9
Sibling Topics
- Pool
- Amateur Extra
- Questions
- 99
- Topic
- Practical circuits and system design
- Region
- US
Read the condition in the stem before comparing key terms in the options.
Study rules, calculations, and equipment questions as separate patterns.
After this topic, return to the full pool for mixed practice.
Topic Study Guide
This topic covers Practical Circuits and System Design (E7) for the Extra Class exam, focusing on digital logic, amplifier classes, filter characteristics, power supplies, DSP/SDR principles, and op-amp gain calculations.
High-Yield Checks
- SDR & DSP Core Concepts: Direct sampling feeds RF straight to an ADC without an LO; Nyquist sampling rate must be at least twice the highest frequency component; 'Taps' in DSP provide incremental signal delays.
- Operational Amplifiers (Op-Amps): Characterized by very high input impedance. The absolute voltage gain for an inverting op-amp is calculated as the feedback resistor divided by the input resistor (RF / R1).
- Filter Characteristics: Elliptical filters have extremely sharp cutoffs with stop-band notches; Cavity filters are used in 2-meter repeater duplexers; a T-network with a shunt inductor is a high-pass filter.
- Amplifier Classes & Configurations: Class D amplifiers use switching technology for high efficiency; Grounded-grid amplifiers are characterized by low input impedance.
Trap Patterns
- Confusing logic gates: It is easy to mix up Exclusive NOR with XOR. Remember that an Exclusive NOR produces a 0 if one and only one input is 1.
- Op-Amp gain calculation errors: When calculating RF / R1, learners often mistakenly divide R1 by RF or forget to convert kilo-ohms to ohms before dividing.
- Misunderstanding power supply components: Confusing an inverter (DC to AC) with a charge controller, or assuming a step-start circuit prevents arcing when its actual purpose is to let filter capacitors charge gradually.
- Name-association traps: Assuming 'Elliptical' means a smooth curve (it's actually very sharp), or associating 'Bistable' with bipolar amplifiers (it actually refers to a flip-flop).
Review Steps
- Step 1: Memorize the two core formulas in this section: Op-Amp gain (RF/R1) and the Nyquist sampling rate (2x the highest frequency).
- Step 2: Group filters and amplifiers by keywords for memorization, such as 'Cavity = Duplexer' and 'Class D = Switching/Efficiency'.
- Step 3: Use the schematic diagrams in the pool (Figures E7-1, E7-2, E7-3) to visually identify the locations of voltage divider bias, bypass capacitors, and feedback resistors.
- Step 4: Review SDR and DSP questions separately to clarify the definitions of direct sampling, anti-aliasing filters, and taps.
Quick Checks
- What is the absolute voltage gain formula for an inverting op-amp?
- Which filter is commonly used in a 2-meter band repeater duplexer?
- What is the minimum sampling rate required to accurately reproduce an analog signal?
- What is the purpose of a step-start circuit in a high-voltage power supply?
Questions in This Topic
Choose Practice ModeE7A01Which circuit is bistable?E7A02What is the function of a decade counter?E7A03Which of the following can divide the frequency of a pulse train by 2?E7A04How many flip-flops are required to divide a signal frequency by 16?E7A05Which of the following circuits continuously alternates between two states without an external clock signal?E7A06What is a characteristic of a monostable multivibrator?E7A07What logical operation does a NAND gate perform?E7A08What logical operation does an OR gate perform?E7A09What logical operation is performed by a two-input exclusive NOR gate?E7A10What is a truth table?E7A11What does “positive logic” mean in reference to logic devices?E7B01For what portion of the signal cycle does each active element in a push-pull, Class AB amplifier conduct?E7B02What is a Class D amplifier?E7B03What circuit is required at the output of an RF switching amplifier?E7B04What is the operating point of a Class A common emitter amplifier?E7B05What can be done to prevent unwanted oscillations in an RF power amplifier?E7B06What is a characteristic of a grounded-grid amplifier?E7B07Which of the following is the likely result of using a Class C amplifier to amplify a single-sideband phone signal?E7B08Why are switching amplifiers more efficient than linear amplifiers?E7B09What is characteristic of an emitter follower (or common collector) amplifier?E7B10In Figure E7-1, what is the purpose of R1 and R2?E7B11In Figure E7-1, what is the purpose of R3?E7B12What type of amplifier circuit is shown in Figure E7-1?E7C01How are the capacitors and inductors of a low-pass filter Pi-network arranged between the network’s input and output?E7C02What is the frequency response of a T-network with series capacitors and a shunt inductor?E7C03What is the purpose of adding an inductor to a Pi-network to create a Pi-L-network?E7C04How does an impedance-matching circuit transform a complex impedance to a resistive impedance?E7C05Which filter type has ripple in the passband and a sharp cutoff?E7C06What are the characteristics of an elliptical filter?E7C07Which describes a Pi-L network?E7C08Which of the following is most frequently used as a band-pass or notch filter in VHF and UHF transceivers?E7C09What is a crystal lattice filter?E7C10Which of the following filters is used in a 2-meter band repeater duplexer?E7C11Which of the following measures a filter’s ability to reject signals in adjacent channels?E7D01How does a linear electronic voltage regulator work?E7D02How does a switchmode voltage regulator work?E7D03What device is used as a stable voltage reference?E7D04Which of the following describes a three-terminal voltage regulator?E7D05Which of the following types of linear voltage regulator operates by loading the unregulated voltage source?E7D06What is the purpose of Q1 in the circuit shown in Figure E7-2?E7D07What is the purpose of C2 in the circuit shown in Figure E7-2?E7D08What type of circuit is shown in Figure E7-2?E7D09How is battery operating time calculated?E7D10Why is a switching type power supply less expensive and lighter than an equivalent linear power supply?E7D11What is the purpose of an inverter connected to a solar panel output?E7D12What is the dropout voltage of a linear voltage regulator?E7D13Which of the following calculates power dissipated by a series linear voltage regulator?E7D14What is the purpose of connecting equal-value resistors across power supply filter capacitors connected in series?E7D15What is the purpose of a step-start circuit in a high-voltage power supply?E7E01Which of the following can be used to generate FM phone signals?E7E02What is the function of a reactance modulator?E7E03What is a frequency discriminator?E7E04What is one way to produce a single-sideband phone signal?E7E05What is added to an FM speech channel to boost the higher audio frequencies?E7E06Why is de-emphasis used in FM communications receivers?E7E07What is meant by the term “baseband” in radio communications?E7E08What are the principal frequencies that appear at the output of a mixer?E7E09What occurs when the input signal levels to a mixer are too high?E7E10How does a diode envelope detector function?E7E11Which type of detector is used for demodulating SSB signals?E7F01What is meant by “direct sampling” in software defined radios?E7F02What kind of digital signal processing audio filter is used to remove unwanted noise from a received SSB signal?E7F03What type of digital signal processing filter is used to generate an SSB signal?E7F04Which method generates an SSB signal using digital signal processing?E7F05How frequently must an analog signal be sampled to be accurately reproduced?E7F06What is the minimum number of bits required to sample a signal with a range of 1 volt at a resolution of 1 millivolt?E7F07What function is performed by a Fast Fourier Transform?E7F08What is the function of decimation?E7F09Why is an anti-aliasing filter required in a decimator?E7F10What aspect of receiver analog-to-digital conversion determines the maximum receive bandwidth of a direct-sampling software defined radio (SDR)?E7F11What sets the minimum detectable signal level for a direct-sampling software defined receiver in the absence of atmospheric or thermal noise?E7F12Which of the following is generally true of Finite Impulse Response (FIR) filters?E7F13What is the function of taps in a digital signal processing filter?E7F14Which of the following would allow a digital signal processing filter to create a sharper filter response?E7G01What is the typical output impedance of an op-amp?E7G02What is the frequency response of the circuit in E7-3 if a capacitor is added across the feedback resistor?E7G03What is the typical input impedance of an op-amp?E7G04What is meant by the term “op-amp input offset voltage”?E7G05How can unwanted ringing and audio instability be prevented in an op-amp audio filter?E7G06What is the gain-bandwidth of an operational amplifier?E7G07What voltage gain can be expected from the circuit in Figure E7-3 when R1 is 10 ohms and RF is 470 ohms?E7G08How does the gain of an ideal operational amplifier vary with frequency?E7G09What will be the output voltage of the circuit shown in Figure E7-3 if R1 is 1,000 ohms, RF is 10,000 ohms, and 0.23 volts DC is applied to the input?E7G10What absolute voltage gain can be expected from the circuit in Figure E7-3 when R1 is 1,800 ohms and RF is 68 kilohms?E7G11What absolute voltage gain can be expected from the circuit in Figure E7-3 when R1 is 3,300 ohms and RF is 47 kilohms?E7G12What is an operational amplifier?E7H01What are three common oscillator circuits?E7H02What is a microphonic?E7H03What is a phase-locked loop?E7H04How is positive feedback supplied in a Colpitts oscillator?E7H05How is positive feedback supplied in a Pierce oscillator?E7H06Which of these functions can be performed by a phase-locked loop?E7H07How can an oscillator’s microphonic responses be reduced?E7H08Which of the following components can be used to reduce thermal drift in crystal oscillators?E7H09What type of frequency synthesizer circuit uses a phase accumulator, lookup table, digital-to-analog converter, and a low-pass anti-alias filter?E7H10What information is contained in the lookup table of a direct digital synthesizer (DDS)?E7H11What are the major spectral impurity components of direct digital synthesizers?E7H12Which of the following ensures that a crystal oscillator operates on the frequency specified by the crystal manufacturer?E7H13Which of the following is a technique for providing highly accurate and stable oscillators needed for microwave transmission and reception?