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Subel. L05
47 questions
Subelement L05

Amplifiers, Mixers and Frequency Multipliers.

Section L05

For what portion of a signal cycle does a Class A amplifier operate?

  • Correct Answer
    The entire cycle
  • Exactly 180 degrees
  • More than 180 degrees but less than 360 degrees
  • Less than 180 degrees

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which class of amplifier has the highest linearity and least distortion?

  • Correct Answer
    Class A
  • Class AB
  • Class B
  • Class C

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For what portion of a cycle does a Class AB amplifier operate?

  • Exactly 180 degrees
  • The entire cycle
  • Less than 180 degrees
  • Correct Answer
    More than 180 degrees but less than 360 degrees

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For what portion of a cycle does a Class B amplifier operate?

  • Correct Answer
    180 degrees
  • Less than 180 degrees
  • More than 180 degrees but less than 360 degrees
  • The entire cycle

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For what portion of a signal cycle does a Class C amplifier operate?

  • The entire cycle
  • 180 degrees
  • Correct Answer
    Less than 180 degrees
  • More than 180 degrees but less than 360 degrees

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following classes of amplifier provides the highest efficiency?

  • Class B
  • Correct Answer
    Class C
  • Class A
  • Class AB

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following classes of amplifier would provide the highest efficiency in the output stage of a CW, RTTY or FM transmitter?

  • Correct Answer
    Class C
  • Class AB
  • Class B
  • Class A

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which class of amplifier provides the least efficiency?

  • Class AB
  • Correct Answer
    Class A
  • Class C
  • Class B

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Which class of amplifier has the poorest linearity and the most distortion?

  • Correct Answer
    Class C
  • Class AB
  • Class A
  • Class B

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Which class of amplifier operates over the full cycle?

  • Class B
  • Class C
  • Correct Answer
    Class A
  • Class AB

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Which class of amplifier operates over less than 180 degrees of the cycle?

  • Correct Answer
    Class C
  • Class AB
  • Class A
  • Class B

Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What determines the input impedance of a FET common-source amplifier?

  • The input impedance is essentially determined by the resistance between the drain and substrate
  • Correct Answer
    The input impedance is essentially determined by the gate biasing network
  • The input impedance is essentially determined by the resistance between the source and substrate
  • The input impedance is essentially determined by the resistance between the source and the drain

The Junction FET is considered a high impedance device. Because the Gate in a Junction FET is always reversed-biased, its input impedance is very high; the input impedance of the whole circuit is determined by the external Gate bias resistor. The output impedance is determined primarily by the resistor acting as a load in the Drain circuit.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What determines the output impedance of a FET common-source amplifier?

  • Correct Answer
    The output impedance is essentially determined by the drain resistor
  • The output impedance is essentially determined by the drain supply voltage
  • The output impedance is essentially determined by the gate supply voltage
  • The output impedance is essentially determined by the input impedance of the FET

The Junction FET is considered a high impedance device. Because the Gate in a Junction FET is always reversed-biased, its input impedance is very high; the input impedance of the whole circuit is determined by the external Gate bias resistor. The output impedance is determined primarily by the resistor acting as a load in the Drain circuit.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What are the advantages of a Darlington pair audio amplifier?

  • Mutual gain, low input impedance and low output impedance
  • Low output impedance, high mutual impedance and low output current
  • Correct Answer
    High gain, high input impedance and low output impedance
  • Mutual gain, high stability and low mutual inductance

The Darlington pair cascades two direct-coupled emitter-follower stages; Beta parameters multiply one another. The emitter follower, just like the cathode follower or the source follower features high input impedance and low output impedance. The Darlington configuration features high gain, high input impedance and low output impedance. "High gain" is enough to identify the correct answer.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In the common base amplifier, when the input and output signals are compared:

  • the signals are 180 degrees out of phase
  • Correct Answer
    the signals are in phase
  • the output signal lags the input signal by 90 degrees
  • the output signals leads the input signal by 90 degrees

Common Emitter: low input Z, medium output Z, 180-degrees phase shift. Common Base: very low input Z, high output Z, no phase shift. Common Collector (Common Drain, Common Plate): high input Z, low output Z, no phase shift, also known as Emitter (Source, Cathode) follower, used for isolation or impedance matching.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In the common base amplifier, the input impedance, when compared to the output impedance is:

  • only slightly lower
  • very high
  • Correct Answer
    very low
  • only slightly higher

Common Emitter: low input Z, medium output Z, 180-degrees phase shift. Common Base: very low input Z, high output Z, no phase shift. Common Collector (Common Drain, Common Plate): high input Z, low output Z, no phase shift, also known as Emitter (Source, Cathode) follower, used for isolation or impedance matching.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In the common emitter amplifier, when the input and output signals are compared:

  • the output signal leads the input signal by 90 degrees
  • the output signal lags the input signal by 90 degrees
  • the signals are in phase
  • Correct Answer
    the signals are 180 degrees out of phase

Common Emitter: low input Z, medium output Z, 180-degrees phase shift. Common Base: very low input Z, high output Z, no phase shift. Common Collector (Common Drain, Common Plate): high input Z, low output Z, no phase shift, also known as Emitter (Source, Cathode) follower, used for isolation or impedance matching.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In the common collector amplifier, when the input and output signals are compared:

  • Correct Answer
    the signals are in phase
  • the output signal leads the input signal by 90 degrees
  • the output signal lags the input signal by 90 degrees
  • the signals are 180 degrees out of phase

Common Emitter: low input Z, medium output Z, 180-degrees phase shift. Common Base: very low input Z, high output Z, no phase shift. Common Collector (Common Drain, Common Plate): high input Z, low output Z, no phase shift, also known as Emitter (Source, Cathode) follower, used for isolation or impedance matching.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The FET amplifier source follower circuit is another name for:

  • common mode circuit
  • common gate circuit
  • Correct Answer
    common drain circuit
  • common source circuit

In a source follower stage, the Source constitutes the output; the Drain, by opposition, must be tied to a common reference (a zero reference for signals): hence the expression, common drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The FET amplifier common source circuit is similar to which of the following bipolar transistor amplifier circuits?

  • Correct Answer
    Common emitter
  • Common collector
  • Common base
  • Common mode

Remember your Basic Qualification? Source, Gate, Drain in the FET compare to Emitter, Base, Collector in the bipolar.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The FET amplifier common drain circuit is similar to which of the following bipolar transistor amplifier circuits?

  • Common mode
  • Correct Answer
    Common collector
  • Common emitter
  • Common base

Remember your Basic Qualification? Source, Gate, Drain in the FET compare to Emitter, Base, Collector in the bipolar.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The FET amplifier common gate circuit is similar to which of the following bipolar transistor amplifier circuits?

  • Common emitter
  • Correct Answer
    Common base
  • Common mode
  • Common collector

Remember your Basic Qualification? Source, Gate, Drain in the FET compare to Emitter, Base, Collector in the bipolar.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is an operational amplifier (op-amp)?

  • An amplifier used to increase the average output of frequency modulated amateur signals to the legal limit
  • A program subroutine that calculates the gain of an RF amplifier
  • Correct Answer
    A high-gain, direct-coupled differential amplifier whose characteristics are determined by components mounted externally
  • A high-gain, direct-coupled audio amplifier whose characteristics are determined by internal components of the device

An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The "ideal" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What would be the characteristics of the ideal op-amp?

  • Zero input impedance, zero output impedance, infinite gain, and flat frequency response
  • Infinite input impedance, infinite output impedance, infinite gain and flat frequency response
  • Zero input impedance, infinite output impedance, infinite gain, and flat frequency response
  • Correct Answer
    Infinite input impedance, zero output impedance, infinite gain, and flat frequency response

An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The "ideal" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What determines the gain of a closed-loop op-amp circuit?

  • The voltage applied to the circuit
  • The collector-to-base capacitance of the PNP stage
  • Correct Answer
    The external feedback network
  • The PNP collector load

An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The "ideal" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is meant by the term op-amp offset voltage?

  • The difference between the output voltage of the op-amp and the input voltage required for the next stage
  • The potential between the amplifier input terminals of the op-amp in an open-loop condition
  • The output voltage of the op-amp minus its input voltage
  • Correct Answer
    The potential between the amplifier input terminals of the op-amp in a closed-loop condition

"Offset voltage is the potential between the amplifier input terminals in the closed-loop condition. Ideally, this voltage would be zero. Offset results from imbalance between the differential input transistors (ARRL Handbook)".

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is the input impedance of a theoretically ideal op-amp?

  • Correct Answer
    Very high
  • Very low
  • Exactly 100 ohms
  • Exactly 1000 ohms

An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The "ideal" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is the output impedance of a theoretically ideal op-amp?

  • Very high
  • Exactly 100 ohms
  • Exactly 1000 ohms
  • Correct Answer
    Very low

An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The "ideal" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What are the advantages of using an op-amp instead of LC elements in an audio filter?

  • Op-amps are more rugged and can withstand more abuse than can LC elements
  • Op-amps are available in more styles and types than are LC elements
  • Op-amps are fixed at one frequency
  • Correct Answer
    Op-amps exhibit gain rather than insertion loss

Inductors and Capacitors are passive components; they inevitably introduce loss. Op-Amps used in filter applications can provide a controlled amount of gain. Op-Amps are commonly used in active AUDIO filter circuits; all types of responses can be implemented (low-pass, high-pass, bandpass, band-stop, a.k.a., notch).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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

  • Op-amp circuits are used as low-pass filters at the output of transmitters
  • Op-amp circuits are used as filters for smoothing power supply output
  • Op-amp circuits are used as high-pass filters to block RFI at the input of receivers
  • Correct Answer
    Op-amp circuits are used as audio filters for receivers

Inductors and Capacitors are passive components; they inevitably introduce loss. Op-Amps used in filter applications can provide a controlled amount of gain. Op-Amps are commonly used in active AUDIO filter circuits; all types of responses can be implemented (low-pass, high-pass, bandpass, band-stop, a.k.a., notch).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is an inverting op-amp circuit?

  • An operational amplifier circuit connected such that the input impedance is held to zero, while the output impedance is high
  • Correct Answer
    An operational amplifier circuit connected such that the input and output signals are 180 degrees out of phase
  • An operational amplifier circuit connected such that the input and output signals are in phase
  • An operational amplifier circuit connected such that the input and output signals are 90 degrees out of phase

An "inverting" Op-Amp circuit introduces a 180-degrees shift: when the input goes up, the output comes down and vice-versa. With the "non-inverting" Op-Amp circuit, the output is in phase with the input.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is a non-inverting op-amp circuit?

  • An operational amplifier circuit connected such that the input and output signals are 90 degrees out of phase
  • An operational amplifier circuit connected such that the input impedance is held low, and the output impedance is high
  • An operational amplifier circuit connected such that the input and output signals are 180 degrees out of phase
  • Correct Answer
    An operational amplifier circuit connected such that the input and output signals are in phase

An "inverting" Op-Amp circuit introduces a 180-degrees shift: when the input goes up, the output comes down and vice-versa. With the "non-inverting" Op-Amp circuit, the output is in phase with the input.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What term is most appropriate for a high gain, direct-coupled differential amplifier whose characteristics are determined by components mounted externally?

  • Summing amplifier
  • Correct Answer
    Operational amplifier
  • Difference amplifier
  • High gain audio amplifier

An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The "ideal" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is the mixing process?

  • The recovery of intelligence from a modulated signal
  • The elimination of noise in a wideband receiver by phase comparison
  • Correct Answer
    The combination of two signals to produce sum and difference frequencies
  • The elimination of noise in a wideband receiver by phase differentiation

A Mixer receives two inputs. They combine within the Mixer to produce two new frequencies: the sum of the inputs and the difference between the inputs. Four frequencies are present at the output: the sum, the difference and the two original frequencies. If a Mixer is driven into non-linearity by excessively strong signals, spurious responses will be produced.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What are the principal frequencies that appear at the output of a mixer circuit?

  • Correct Answer
    The original frequencies and the sum and difference frequencies
  • 1.414 and 0.707 times the input frequencies
  • The sum, difference and square root of the input frequencies
  • Two and four times the original frequency

A Mixer receives two inputs. They combine within the Mixer to produce two new frequencies: the sum of the inputs and the difference between the inputs. Four frequencies are present at the output: the sum, the difference and the two original frequencies. If a Mixer is driven into non-linearity by excessively strong signals, spurious responses will be produced.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What occurs when an excessive amount of signal energy reaches the mixer circuit?

  • Mixer blanking occurs
  • Correct Answer
    Spurious signals are generated
  • Automatic limiting occurs
  • A beat frequency is generated

A Mixer receives two inputs. They combine within the Mixer to produce two new frequencies: the sum of the inputs and the difference between the inputs. Four frequencies are present at the output: the sum, the difference and the two original frequencies. If a Mixer is driven into non-linearity by excessively strong signals, spurious responses will be produced.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a frequency multiplier circuit, the input signal is coupled to the base of a transistor through a capacitor. A radio frequency choke is connected between the base of the transistor and ground. The capacitor is:

  • part of the input tuned circuit
  • a by-pass for the circuit
  • part of the output tank circuit
  • Correct Answer
    a DC blocking capacitor

A capacitor used for coupling let AC signals through but blocks DC.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A frequency multiplier circuit must be operated in:

  • Correct Answer
    class C
  • class AB
  • class B
  • class A

A Frequency-Multiplier stage relies on harmonics produced by a gain device operated in Class C. The output circuit is tuned to an exact multiple of the input frequency (harmonic, typically two to four times). If greater multiplication is required, a chain of stages will be used.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a frequency multiplier circuit, an inductance (L1) and a variable capacitor (C2) are connected in series between VCC+ and ground. The collector of a transistor is connected to a tap on L1. The purpose of the variable capacitor is to:

  • Correct Answer
    tune L1 to the desired harmonic
  • by-pass RF
  • tune L1 to the frequency applied to the base
  • provide positive feedback

A tuned circuit is present in the output of a frequency multiplier to select the desired harmonic and reject unwanted signals.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a frequency multiplier circuit, an inductance (L1) and a variable capacitor (C2) are connected in series between VCC+ and ground. The collector of a transistor is connected to a tap on L1. A fixed capacitor (C3) is connected between the VCC+ side of L1 and ground. The purpose of C3 is to:

  • resonate with L1
  • by-pass any audio components
  • Correct Answer
    provide an RF ground at the VCC connection point of L1
  • form a pi filter with L1 and C2

A capacitor between the supply and ground is a "bypass" capacitor, it serves two purposes: it provides a low-impedance path to complete the AC circuit and it keeps AC signals out of the supply line (through which they could affect other stages). This being a frequency multiplier, the capacitor is an RF bypass.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a frequency multiplier circuit, an inductance (L1) and a variable capacitor (C2) are connected in series between VCC+ and ground. The collector of a transistor is connected to a tap on L1. C2 in conjunction with L1 operate as a:

  • voltage doubler
  • Correct Answer
    frequency multiplier
  • frequency divider
  • voltage divider

A tuned circuit is present in the output of a frequency multiplier to select the desired harmonic and reject unwanted signals.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a circuit where the components are tuned to resonate at a higher frequency than applied, the circuit is most likely a:

  • a frequency divider
  • Correct Answer
    a frequency multiplier
  • a VHF/UHF amplifier
  • a linear amplifier

A Frequency-Multiplier stage relies on harmonics produced by a gain device operated in Class C. The output circuit is tuned to an exact multiple of the input frequency (harmonic, typically two to four times). If greater multiplication is required, a chain of stages will be used.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a frequency multiplier circuit, an inductance (L1) and a variable capacitor (C2) are connected in series between VCC+ and ground. The collector of a transistor is connected to a tap on L1. A fixed capacitor (C3) is connected between the VCC+ side of L1 and ground. C3 is a:

  • DC blocking capacitor
  • tuning capacitor
  • coupling capacitor
  • Correct Answer
    RF by-pass capacitor

A capacitor between the supply and ground is a "bypass" capacitor, it serves two purposes: it provides a low-impedance path to complete the AC circuit and it keeps AC signals out of the supply line (through which they could affect other stages). This being a frequency multiplier, the capacitor is an RF bypass.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What stage in a transmitter would change a 5.3-MHz input signal to 14.3 MHz?

  • A frequency multiplier
  • A beat frequency oscillator
  • Correct Answer
    A mixer
  • A linear translator

The second frequency is not a multiple of the first, this excludes the multiplier. A Frequency Multiplier stage relies on harmonics produced by a gain device operated in Class C. The output circuit is tuned to an exact multiple of the input frequency (harmonic, typically two to four times). If greater multiplication is required, a chain of stages will be used.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The main advantage of a crystal oscillator over a tuned LC oscillator is:

  • freedom from harmonic emissions
  • simplicity
  • Correct Answer
    much greater frequency stability
  • longer life under severe operating use

Piezoelectric crystals behave like tuned circuits with an extremely high "Q" ("Quality Factor", in excess of 25 000). Their accuracy and stability are outstanding.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Crystals are sometimes used in a circuit which has an output close to an integral multiple of the crystal frequency. This circuit is called:

  • a crystal ladder
  • Correct Answer
    an overtone oscillator
  • a crystal multiplier
  • a crystal lattice

Key word: MULTIPLE. Crystals are capable of resonance either at a fundamental frequency depending on their physical dimensions or at overtone frequencies near odd-integer multiples (3rd, 5th, 7th, etc.) of the fundamental. In a filter, crystals are used at their fundamental frequencies; the crystal lattice filter and the crystal ladder filter are two typical configurations. Crystal oscillators can be designed to work on a fundamental or overtone resonance; crystals are manufactured accordingly.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following properties does not apply to a crystal when used in an oscillator circuit?

  • Good frequency accuracy
  • Correct Answer
    High power output
  • Good frequency stability
  • Very low noise because of high Q

The piezoelectric property of quartz is two-fold: apply mechanical stress to a crystal and it produces a small electrical field; subject quartz to an electrical field and the crystal changes dimensions slightly. Crystals are capable of resonance either at a fundamental frequency depending on their physical dimensions or at overtone frequencies near odd-integer multiples (3rd, 5th, 7th, etc.). Piezoelectric crystals can serve as filters because of their extremely high "Q" (> 25 000) or as stable, noise-free and accurate frequency references.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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