FREE HAM Radio Extra Class Test Practical Circuits and Components Questions and Answers Flashcards

What is the effect of adding a ferrite bead to a power supply lead in an RF circuit?

Answer: It suppresses high-frequency parasitic oscillations and RF interference

Ferrite beads act as lossy inductors at RF frequencies, absorbing high-frequency energy and preventing parasitic oscillations or conducted RF interference on power leads.

In a direct digital synthesis (DDS) system, what determines the frequency resolution of the output signal?

Answer: The size of the phase accumulator and the clock frequency

Frequency resolution in a DDS is set by dividing the clock frequency by 2 raised to the power of the phase accumulator bit width.

What is the purpose of a cascode configuration in an RF preamplifier?

Answer: To reduce the Miller effect and improve high-frequency gain

The cascode configuration stacks a common-emitter stage with a common-base stage, which drastically reduces Miller capacitance and improves gain-bandwidth product.

What is the typical purpose of a PIN diode in an antenna switching circuit?

Answer: To act as a current-controlled RF switch with low distortion

PIN diodes behave as variable resistors at RF frequencies controlled by DC bias current, making them ideal low-distortion switches for antenna routing.

Why is a Zener diode sometimes placed across the gate of a MOSFET in an RF power amplifier?

Answer: To protect the gate oxide from excessive voltage spikes

MOSFET gate oxide is extremely thin and can be destroyed by voltage spikes; a Zener diode clamps the gate voltage to a safe level.

What advantage does a log-periodic amplifier offer compared to a single-tuned amplifier in a wideband receiver?

Answer: Relatively constant gain over a wide frequency range

Log-periodic amplifier designs provide approximately uniform gain across a wide bandwidth, making them suitable for broadband receiver front ends.