Amateur Extra E7E: Modulators, mixers and detectors
These are the 11 official questions in group E7E of the 2024–2028 Amateur Extra question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
- E7E01Question 1
Which of the following can be used to generate FM phone signals?
- ABalanced modulation of the audio amplifier
- BReactance modulation of a local oscillator Correct
- CReactance modulation of the final amplifier
- DBalanced modulation of a local oscillator
Why: Reactance modulation of a local oscillator can produce FM.
- E7E02Question 2
What is the function of a reactance modulator?
- AProduce PM or FM signals by varying a resistance
- BProduce AM signals by varying an inductance
- CProduce AM signals by varying a resistance
- DProduce PM or FM signals by varying a capacitance Correct
Why: A reactance modulator varies a capacitance to make PM or FM.
- E7E03Question 3
What is a frequency discriminator?
- AAn FM generator circuit
- BA circuit for filtering closely adjacent signals
- CAn automatic band-switching circuit
- DA circuit for detecting FM signals Correct
Why: A frequency discriminator detects FM.
- E7E04Question 4
What is one way to produce a single-sideband phone signal?
- AUse a balanced modulator followed by a filter Correct
- BUse a reactance modulator followed by a mixer
- CUse a loop modulator followed by a mixer
- DUse a product detector with a DSB signal
Why: A balanced modulator followed by a filter makes SSB.
- E7E05Question 5
What is added to an FM speech channel to boost the higher audio frequencies?
- AA de-emphasis network
- BA harmonic enhancer
- CA heterodyne enhancer
- DA pre-emphasis network Correct
Why: A pre-emphasis network boosts the higher audio frequencies.
- E7E06Question 6
Why is de-emphasis used in FM communications receivers?
- AFor compatibility with transmitters using phase modulation Correct
- BTo reduce impulse noise reception
- CFor higher efficiency
- DTo remove third-order distortion products
Why: De-emphasis keeps receivers compatible with phase-modulated transmitters.
- E7E07Question 7
What is meant by the term “baseband” in radio communications?
- AThe lowest frequency band that the transmitter or receiver covers
- BThe frequency range occupied by a message signal prior to modulation Correct
- CThe unmodulated bandwidth of the transmitted signal
- DThe basic oscillator frequency in an FM transmitter that is multiplied to increase the deviation and carrier frequency
Why: Baseband is the message's frequency range before modulation.
- E7E08Question 8
What are the principal frequencies that appear at the output of a mixer?
- ATwo and four times the input frequency
- BThe square root of the product of input frequencies
- CThe two input frequencies along with their sum and difference frequencies Correct
- D1.414 and 0.707 times the input frequency
Why: A mixer outputs the two input frequencies and their sum and difference.
- E7E09Question 9
What occurs when the input signal levels to a mixer are too high?
- ASpurious mixer products are generated Correct
- BMixer blanking occurs
- CAutomatic limiting occurs
- DExcessive AGC voltage levels are generated
Why: Overdriving a mixer creates spurious products.
- E7E10Question 10
How does a diode envelope detector function?
- ABy rectification and filtering of RF signals Correct
- BBy breakdown of the Zener voltage
- CBy mixing signals with noise in the transition region of the diode
- DBy sensing the change of reactance in the diode with respect to frequency
Why: An envelope detector rectifies and filters the RF.
- E7E11Question 11
Which type of detector is used for demodulating SSB signals?
- ADiscriminator
- BPhase detector
- CProduct detector Correct
- DPhase comparator
Why: SSB is demodulated with a product detector.