Amateur Extra E4A: Oscilloscopes, spectrum analyzers and antenna analyzers
These are the 11 official questions in group E4A 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.
- E4A01Question 1
Which of the following limits the highest frequency signal that can be accurately displayed on a digital oscilloscope?
- ASampling rate of the analog-to-digital converter Correct
- BAnalog-to-digital converter reference frequency
- CQ of the circuit
- DAll these choices are correct
Why: The ADC sampling rate limits the highest frequency a digital scope can show accurately.
- E4A02Question 2
Which of the following parameters does a spectrum analyzer display on the vertical and horizontal axes?
- ASignal amplitude and time
- BSignal amplitude and frequency Correct
- CSWR and frequency
- DSWR and time
Why: A spectrum analyzer shows amplitude vertically and frequency horizontally.
- E4A03Question 3
Which of the following test instruments is used to display spurious signals and/or intermodulation distortion products generated by an SSB transmitter?
- ADifferential resolver
- BSpectrum analyzer Correct
- CLogic analyzer
- DNetwork analyzer
Why: A spectrum analyzer shows spurious signals and intermod products.
- E4A04Question 4
How is compensation of an oscilloscope probe performed?
- AA square wave is displayed, and the probe is adjusted until the horizontal portions of the displayed wave are as nearly flat as possible Correct
- BA high frequency sine wave is displayed, and the probe is adjusted for maximum amplitude
- CA frequency standard is displayed, and the probe is adjusted until the deflection time is accurate
- DA DC voltage standard is displayed, and the probe is adjusted until the displayed voltage is accurate
Why: Display a square wave and adjust the probe until the flat parts are as flat as possible.
- E4A05Question 5
What is the purpose of using a prescaler with a frequency counter?
- AAmplify low-level signals for more accurate counting
- BMultiply a higher frequency signal so a low-frequency counter can display the operating frequency
- CPrevent oscillation in a low-frequency counter circuit
- DReduce the signal frequency to within the counter's operating range Correct
Why: A prescaler divides the frequency down into the counter's range.
- E4A06Question 6
What is the effect of aliasing on a digital oscilloscope when displaying a waveform?
- AA false, jittery low-frequency version of the waveform is displayed Correct
- BThe waveform DC offset will be inaccurate
- CCalibration of the vertical scale is no longer valid
- DExcessive blanking occurs, which prevents display of the waveform
Why: Aliasing shows a false, jittery low-frequency version of the waveform.
- E4A07Question 7
Which of the following is an advantage of using an antenna analyzer compared to an SWR bridge?
- AAntenna analyzers automatically tune your antenna for resonance
- BAntenna analyzers compute SWR and impedance automatically Correct
- CAntenna analyzers display a time-varying representation of the modulation envelope
- DAll these choices are correct
Why: An antenna analyzer computes SWR and impedance automatically.
- E4A08Question 8
Which of the following is used to measure SWR?
- ADirectional wattmeter
- BVector network analyzer
- CAntenna analyzer
- DAll these choices are correct Correct
Why: Directional wattmeters, analyzers and network analyzers can all measure SWR. All the choices are correct.
- E4A09Question 9
Which of the following is good practice when using an oscilloscope probe?
- AMinimize the length of the probe's ground connection Correct
- BNever use a high-impedance probe to measure a low-impedance circuit
- CNever use a DC-coupled probe to measure an AC circuit
- DAll these choices are correct
Why: Keep the probe's ground connection short.
- E4A10Question 10
Which trigger mode is most effective when using an oscilloscope to measure a linear power supply’s output ripple?
- ASingle-shot
- BEdge
- CLevel
- DLine Correct
Why: Line triggering syncs to the AC power line, which matches ripple.
- E4A11Question 11
Which of the following can be measured with an antenna analyzer?
- AVelocity factor
- BCable length
- CResonant frequency of a tuned circuit
- DAll these choices are correct Correct
Why: An antenna analyzer can measure SWR, impedance and more. All the choices are correct.