Amateur Extra E7C: Filters and matching networks
These are the 11 official questions in group E7C 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.
- E7C01Question 1
How are the capacitors and inductors of a low-pass filter Pi-network arranged between the network’s input and output?
- ATwo inductors are in series between the input and output, and a capacitor is connected between the two inductors and ground
- BTwo capacitors are in series between the input and output, and an inductor is connected between the two capacitors and ground
- CAn inductor is connected between the input and ground, another inductor is connected between the output and ground, and a capacitor is connected between the input and output
- DA capacitor is connected between the input and ground, another capacitor is connected between the output and ground, and an inductor is connected between the input and output Correct
Why: Capacitors from input and output to ground, with an inductor between them.
- E7C02Question 2
What is the frequency response of a T-network with series capacitors and a shunt inductor?
- ALow-pass
- BHigh-pass Correct
- CBand-pass
- DNotch
Why: Series capacitors and a shunt inductor make a high-pass T network.
- E7C03Question 3
What is the purpose of adding an inductor to a Pi-network to create a Pi-L-network?
- AGreater harmonic suppression Correct
- BHigher efficiency
- CTo eliminate one capacitor
- DGreater transformation range
Why: The extra inductor gives more harmonic suppression.
- E7C04Question 4
How does an impedance-matching circuit transform a complex impedance to a resistive impedance?
- AIt introduces negative resistance to cancel the resistive part of impedance
- BIt introduces transconductance to cancel the reactive part of impedance
- CIt cancels the reactive part of the impedance and changes the resistive part to the desired value Correct
- DReactive currents are dissipated in matched resistances
Why: It cancels the reactance and transforms the resistance to the desired value.
- E7C05Question 5
Which filter type has ripple in the passband and a sharp cutoff?
- AA Butterworth filter
- BAn active LC filter
- CA passive op-amp filter
- DA Chebyshev filter Correct
Why: Chebyshev filters have passband ripple and a sharp cutoff.
- E7C06Question 6
What are the characteristics of an elliptical filter?
- AGradual passband rolloff with minimal stop-band ripple
- BExtremely flat response over its pass band with gradually rounded stop-band corners
- CExtremely sharp cutoff with one or more notches in the stop band Correct
- DGradual passband rolloff with extreme stop-band ripple
Why: Elliptical filters cut off extremely sharply and have notches in the stopband.
- E7C07Question 7
Which describes a Pi-L network?
- AA Phase Inverter Load network
- BA Pi-network with an additional output series inductor Correct
- CA network with only three discrete parts
- DA matching network in which all components are isolated from ground
Why: A Pi-L is a Pi network with an extra series output inductor.
- E7C08Question 8
Which of the following is most frequently used as a band-pass or notch filter in VHF and UHF transceivers?
- AA Sallen-Key filter
- BA helical filter Correct
- CA swinging choke filter
- DA finite impulse response filter
Why: Helical filters are common in VHF and UHF radios.
- E7C09Question 9
What is a crystal lattice filter?
- AA power supply filter made with interlaced quartz crystals
- BAn audio filter made with four quartz crystals that resonate at 1 kHz intervals
- CA filter using lattice-shaped quartz crystals for high-Q performance
- DA filter for low-level signals made using quartz crystals Correct
Why: A crystal lattice filter uses quartz crystals for low-level signals.
- E7C10Question 10
Which of the following filters is used in a 2-meter band repeater duplexer?
- AA crystal filter
- BA cavity filter Correct
- CA DSP filter
- DAn L-C filter
Why: Repeater duplexers use cavity filters.
- E7C11Question 11
Which of the following measures a filter’s ability to reject signals in adjacent channels?
- APassband ripple
- BPhase response
- CShape factor Correct
- DNoise factor
Why: Shape factor measures adjacent-channel rejection.