Amateur Extra E4B: Measurement accuracy and network analyzers
These are the 11 official questions in group E4B 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.
- E4B01Question 1
Which of the following factors most affects the accuracy of a frequency counter?
- AInput attenuator accuracy
- BTime base accuracy Correct
- CDecade divider accuracy
- DTemperature coefficient of the logic
Why: A frequency counter is only as accurate as its time base.
- E4B02Question 2
What is the significance of voltmeter sensitivity expressed in ohms per volt?
- AThe full scale reading of the voltmeter multiplied by its ohms per volt rating is the input impedance of the voltmeter Correct
- BThe reading in volts multiplied by the ohms per volt rating will determine the power drawn by the device under test
- CThe reading in ohms divided by the ohms per volt rating will determine the voltage applied to the circuit
- DThe full scale reading in amps divided by ohms per volt rating will determine the size of shunt needed
Why: Ohms per volt × full-scale reading = the voltmeter's input impedance.
- E4B03Question 3
Which S parameter is equivalent to forward gain?
- AS11
- BS12
- CS21 Correct
- DS22
Why: S21 is forward gain.
- E4B04Question 4
Which S parameter represents input port return loss or reflection coefficient (equivalent to VSWR)?
- AS11 Correct
- BS12
- CS21
- DS22
Why: S11 is the input's return loss or reflection coefficient.
- E4B05Question 5
What three test loads are used to calibrate an RF vector network analyzer?
- A50 ohms, 75 ohms, and 90 ohms
- BShort circuit, open circuit, and 50 ohms Correct
- CShort circuit, open circuit, and resonant circuit
- D50 ohms through 1/8 wavelength, 1/4 wavelength, and 1/2 wavelength of coaxial cable
Why: VNA calibration uses a short, an open and a 50 Ω load.
- E4B06Question 6
How much power is being absorbed by the load when a directional power meter connected between a transmitter and a terminating load reads 100 watts forward power and 25 watts reflected power?
- A100 watts
- B125 watts
- C112.5 watts
- D75 watts Correct
Why: 100 W forward − 25 W reflected = 75 W absorbed.
- E4B07Question 7
What do the subscripts of S parameters represent?
- AThe port or ports at which measurements are made Correct
- BThe relative time between measurements
- CRelative quality of the data
- DFrequency order of the measurements
Why: S-parameter subscripts name the ports being measured.
- E4B08Question 8
Which of the following can be used to determine the Q of a series-tuned circuit?
- AThe ratio of inductive reactance to capacitive reactance
- BThe frequency shift
- CThe bandwidth of the circuit's frequency response Correct
- DThe resonant frequency of the circuit
Why: Q can be found from the bandwidth of the frequency response.
- E4B09Question 9
Which of the following can be measured by a two-port vector network analyzer?
- APhase noise
- BFilter frequency response Correct
- CPulse rise time
- DForward power
Why: A two-port VNA can measure a filter's frequency response.
- E4B10Question 10
Which of the following methods measures intermodulation distortion in an SSB transmitter?
- AModulate the transmitter using two RF signals having non-harmonically related frequencies and observe the RF output with a spectrum analyzer
- BModulate the transmitter using two AF signals having non-harmonically related frequencies and observe the RF output with a spectrum analyzer Correct
- CModulate the transmitter using two AF signals having harmonically related frequencies and observe the RF output with a peak reading wattmeter
- DModulate the transmitter using two RF signals having harmonically related frequencies and observe the RF output with a logic analyzer
Why: Use two non-harmonically related audio tones and watch the RF output on a spectrum analyzer.
- E4B11Question 11
Which of the following can be measured with a vector network analyzer?
- AInput impedance
- BOutput impedance
- CReflection coefficient
- DAll these choices are correct Correct
Why: A VNA can measure many parameters. All the choices are correct.