# Practical Circuits

E7A01 (C)What is a bistable multivibrator circuit?

C. A flip-flop

E7A02 (C)How many output level changes are obtained for every two trigger pulses applied to the input of a "T" flip-flop circuit?

C. Two

E7A03 (B)The frequency of an AC signal can be divided electronically by what type of digital circuit?

B. A bistable multivibrator

E7A04 (B)How many flip-flops are required to divide a signal frequency by 4?

B. 2

E7A05 (D)What is the characteristic function of an astable multivibrator?

D. It alternates between two unstable states

E7A06 (A)What is the characteristic function of a monostable multivibrator?

A. It switches momentarily to the opposite binary state and then returns after a set time to its original state

E7A07 (B)What logical operation does an AND gate perform?

B. It produces a logic "1" at its output only if all inputs are logic "1"

E7A08 (D)What logical operation does a NAND gate perform?

D. It produces a logic "0" at its output only when all inputs are logic "1"

E7A09 (A)What logical operation does an OR gate perform?

A. It produces a logic "1" at its output if any input is or all inputs are logic "1"

E7A10 (C) What logical operation does a NOR gate perform?

C. It produces a logic "0" at its output if any input is or all inputs are logic "1"

E7A11 (C)What is a truth table?

C. A list of input combinations and their corresponding outputs that characterize the function of a digital device

E7A12 (D)In a positive-logic circuit, what level is used to represent a logic 1?

D. A high level

E7A13 (A)In a negative-logic circuit, what level is used to represent a logic 1?

A. A low level

E7B01 (A)For what portion of a signal cycle does a Class AB amplifier operate?

A. More than 180 degrees but less than 360 degrees

E7B02 (C)Which class of amplifier provides the highest efficiency?

C. Class C

E7B03 (A)Where on the load line should a bipolar-transistor, common-emitter Class A power amplifier be operated for best efficiency and stability?

A. Below the saturation region

E7B04 (C)How can parasitic oscillations be eliminated from a power amplifier?

C. By neutralization

E7B05 (B)How can even-order harmonics be reduced or prevented in transmitter amplifiers?

B. By using a push-pull amplifier

E7B06 (D)What can occur when a nonlinear amplifier is used with a single-sideband phone transmitter?

D. Distortion

E7B07 (C)How can a vacuum-tube power amplifier be neutralized?

C. By feeding back an out-of-phase component of the output to the input

E7B08 (D)What is the procedure for tuning a vacuum-tube power amplifier having an output pi-network?

D. Alternately increase the plate current with the loading capacitor and dip the plate current with the tuning capacitor

E7B09 (B)In Figure E7-1, what is the purpose of R1 and R2?

B. Fixed bias

E7B10 (D)In Figure E7-1, what is the purpose of C3?

D. Emitter bypass

E7B11 (D)In Figure E7-1, what is the purpose of R3?

D. Self bias

E7B12 (C)What type of circuit is shown in Figure E7-1?

C. Common emitter amplifier

E7B13 (D)In Figure E7-1, what is the purpose of C1?

D. Input coupling

E7B14 (A)In Figure E7-2, what is the purpose of R?

E7B15 (A)In Figure E7-2, what is the purpose of C2?

A. Output coupling

E7B16 (B)What is the purpose of D1 in the circuit shown in Figure E7-3?

B. Voltage reference

E7B17 (C)What is the purpose of Q1 in the circuit shown in Figure E7-3?

C. It increases the current-handling capability

E7B18 (A)What is the purpose of C2 in the circuit shown in Figure E7-3?

A. It bypasses hum around D1

E7B19 (C)What type of circuit is shown in Figure E7-3?

C. Linear voltage regulator

E7B20 (D)What is the purpose of C1 in the circuit shown in Figure E7-3?

D. It filters the supply voltage

E7B21 (A)What is the purpose of C3 in the circuit shown in Figure E7-3?

A. It prevents self-oscillation

E7B22 (C)What is the purpose of R1 in the circuit shown in Figure E7-3?

C. It supplies current to D1

E7B23 (D)What is the purpose of R2 in the circuit shown in Figure E7-3?

D. It provides a constant minimum load for Q1

E7C01 (D)How are the capacitors and inductors of a low-pass filter pi-network arranged between the network's input and output?

D. A capacitor is in parallel with the input, another capacitor is in parallel with the output, and an inductor is in series between the two

E7C02 (B)What is an L-network?

B. A network consisting of an inductor and a capacitor

E7C03 (C)A T-network with series capacitors and a parallel (shunt) inductor has which of the following properties?

C. It transforms impedances and is a high-pass filter

E7C04 (A)What advantage does a pi-L-network have over a pi-network for impedance matching between the final amplifier of a vacuum-tube type transmitter and a multiband antenna?

A. Greater harmonic suppression

E7C05 (C)How does a network transform one impedance to another?

C. It cancels the reactive part of an impedance and changes the resistive part

E7C06 (D)Which filter type is described as having ripple in the passband and a sharp cutoff?

D. A Chebyshev filter

E7C07 (C) What are the distinguishing features of an elliptical filter?

C. Extremely sharp cutoff, with one or more infinitely deep notches in the stop band

E7C08 (B)What kind of audio filter would you use to attenuate an interfering carrier signal while receiving an SSB transmission?

B. A notch filter

E7C09 (D)What characteristic do typical SSB receiver IF filters lack that is important to digital communications?

D. Linear phase response

E7C10 (A)What kind of digital signal processing audio filter might be used to remove unwanted noise from a received SSB signal?

E7C11 (C) What kind of digital signal processing filter might be used ingenerating an SSB signal?

C. A Hilbert-transform filter

E7C12 (B)Which type of filter would be the best to use in a 2-meter repeater duplexer?

B. A cavity filter

E7C13 (D)What is a pi-network?

D. A network consisting of one inductor and two capacitors or two inductors and one capacitor

E7C14 (B)What is a pi-L-network?

B. A network consisting of two inductors and two capacitors

E7C15 (C)Which type of network provides the greatest harmonic suppression?

C. Pi-L-network

E7D01 (D)What are three major oscillator circuits often used in Amateur Radio equipment?

D. Colpitts, Hartley and Pierce

E7D02 (C)What condition must exist for a circuit to oscillate?

C. It must have positive feedback sufficient to overcome losses

E7D03 (A)How is the positive feedback coupled to the input in a Hartley oscillator?

A. Through a tapped coil

E7D04 (C)How is the positive feedback coupled to the input in a Colpitts oscillator?

C. Through a capacitive divider

E7D05 (D)How is the positive feedback coupled to the input in a Pierce oscillator?

D. Through a quartz crystal

E7D06 (B)Which type of oscillator circuits are commonly used in a VFO?

B. Colpitts and Hartley

E7D07 (B)Why is very stable reference oscillator normally used as part of a phase-locked loop (PLL) frequency synthesizer?

B. Any phase variations in the reference oscillator signal will produce phase noise in the synthesizer output

E7D08 (D)What is one characteristic of a linear electronic voltage regulator?

D. The conduction of a control element is varied in direct proportion to the load current to maintain a constant output voltage

E7D09 (C) What is one characteristic of a switching electronic voltage regulator?

C. The control device is switched on or off, with the duty cycle automatically adjusted to maintain a constant average output voltage

E7D10 (A)What device is typically used as a stable reference voltage in a linear voltage regulator?

A. A Zener diode

E7D11 (B)What type of linear regulator is used in applications requiring efficient use of the primary power source?

B. A series regulator

E7D12 (D)What type of linear voltage regulator is used in applications requiring a constant load on the unregulated voltage source?

D. A shunt regulator

E7D13 (C)Which of the following Zener diodes voltages will result in the best temperature stability for a voltage reference?

C. 5.6 volts

E7D14 (B)What are the important characteristics of a three-terminal regulator?

B. Maximum and minimum input voltage, maximum and minimum output current and maximum output voltage

E7D15 (A)What type of voltage regulator limits the voltage drop across its junction when a specified current passes through it in the reverse-breakdown direction?

A. A Zener diode

E7E01 (B)How is an F3E FM-phone emission produced?

B. With a reactance modulator on the oscillator

E7E02 (C)How does a reactance modulator work?

C. It acts as a variable inductance or capacitance to produce FM signals

E7E03 (C)How does a phase modulator work?

C. It varies the tuning of an amplifier tank circuit to produce PM signals

E7E04 (A)How can a single-sideband phone signal be generated?

A. By using a balanced modulator followed by a filter

E7E05 (D)What audio shaping network is added at a transmitter to proportionally attenuate the lower audio frequencies, giving an even spread to the energy in the audio band?

D. A pre-emphasis network

E7E06 (A)What audio shaping network is added at a receiver to restore proportionally attenuated lower audio frequencies?

A. A de-emphasis network

E7E07 (D)What is the mixing process?

D. The combination of two signals to produce sum and difference frequencies

E7E08 (C)What are the principal frequencies that appear at the output of a mixer circuit?

C. The original frequencies and the sum and difference frequencies

E7E09 (A)What occurs in a receiver when an excessive amount of signal energy reaches the mixer circuit?

A. Spurious mixer products are generated

E7E10 (C)What type of frequency synthesizer circuit uses a stable voltage-controlled oscillator, programmable divider, phase detector, loop filter and a reference frequency source?

C. A phase-locked loop synthesizer

E7E11 (A)What type of frequency synthesizer circuit uses a phase accumulator, lookup table, digital to analog converter and a low-pass antialias filter?

A. A direct digital synthesizer

E7E12 (D)What are the main blocks of a direct digital frequency synthesizer?

D. A phase accumulator, lookup table, digital to analog converter and a low-pass antialias filter

E7E13 (B)What information is contained in the lookup table of a direct digital frequency synthesizer?

B. The amplitude values that represent a sine-wave output

E7E14 (C)What are the major spectral impurity components of direct digital synthesizers?

C. Spurs at discrete frequencies

E7E15 (A)What are the major spectral impurity components of phase-locked loop synthesizers?

E7E16 (B)What is the process of detection?

B. The recovery of the intelligence from a modulated RF signal

E7E17 (A)What is the principle of detection in a diode detector?

A. Rectification and filtering of RF

E7E18 (C)What does a product detector do?

C. It mixes an incoming signal with a locally generated carrier

E7E19 (B)How are FM-phone signals detected?

B. With a frequency discriminator

E7E20 (D)What is a frequency discriminator?

D. A circuit for detecting FM signals

E7E21 (C)How can an FM-phone signal be produced?

C. By using a reactance modulator on an oscillator

E7F01 (D)What is the purpose of a prescaler circuit?

D. It divides an HF signal so a low-frequency counter can display the operating frequency

E7F02 (B)How many states does a decade counter digital IC have?

B. 10

E7F03 (A)What is the function of a decade counter digital IC?

A. It produces one output pulse for every ten input pulses

E7F04 (C) What additional circuitry is required in a 100-kHz crystal-controlled marker generator to provide markers at 50 and 25 kHz?

C. Two flip-flops

E7F05 (B)If a 1-MHz oscillator is used with a divide-by-ten circuit to make a marker generator, what will the output be?

B. A 100-kHz signal with harmonics every 100 kHz

E7F06 (D)What is a crystal-controlled marker generator?

D. A high-stability oscillator that generates a series of reference signals at known frequency intervals

E7F07 (A)What type of circuit does NOT make a good marker generator?

A. A sinusoidal crystal oscillator

E7F08 (C)What is the purpose of a marker generator?

C. To provide a means of calibrating a receiver's frequency settings

E7F09 (A)What does the accuracy of a frequency counter depend on?

A. The internal crystal reference

E7F10 (C)How does a frequency counter determine the frequency of a signal?

C. It counts the number of input pulses in a specific period of time

E7F11 (A)What is the purpose of a frequency counter?

A. To indicate the frequency of the strongest input signal which is within the counter's frequency range

E7G01 (B)What determines the gain and frequency characteristics of an op-amp RC active filter?

B. The values of capacitances and resistances external to the op-amp

E7G02 (C)What causes ringing in a filter?

C. The filter shape, as measured in the frequency domain

E7G03 (D)What are the advantages of using an op-amp instead of LC elements inan audio filter?

D. Op-amps exhibit gain rather than insertion loss

E7G04 (C)What type of capacitors should be used in a high-stability op-amp RC active filter circuit?

C. Polystyrene

E7G05 (A)How can unwanted ringing and audio instability be prevented in a multisection op-amp RC audio filter circuit?

A. Restrict both gain and Q

E7G06 (A)What parameter must be selected when selecting the resistor and capacitor values for an RC active filter using an op-amp?

A. Filter bandwidth

E7G07 (B)The design of a preselector involves a trade-off between bandwidth and what other factor?

B. Insertion loss

E7G08 (A)When designing an op-amp RC active filter for a given frequency range and Q, what steps are typically followed when selecting the external components?

A. Standard capacitor values are chosen first, the resistances are calculated, then resistors of the nearest standard value are used

E7G09 (C)When designing an op-amp RC active filter for a given frequency range and Q, why are the external capacitance values usually chosen first, then the external resistance values calculated?

C. Capacitors with unusual capacitance values are not widely available, so standard values are used to begin the calculations

E7G10 (D)What are the principal uses of an op-amp RC active filter in amateur circuitry?

D. Audio filters used for receivers

E7G11 (D)Where should an op-amp RC active audio filter be placed in an amateur receiver?

D. In the low-level audio stages