Practical Electronics Circuits Flashcards
7 cards from real HAM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Practical Electronics Circuits flashcards as text
What is the purpose of a PIN diode in an RF switching circuit?
Answer: To act as a variable resistance controlled by DC bias current
A PIN diode's intrinsic region resistance is controlled by DC bias, allowing it to act as a voltage-controlled switch or attenuator at RF frequencies.
In a phase-locked loop (PLL), what does the voltage-controlled oscillator (VCO) receive as its control input?
Answer: The filtered error voltage from the phase detector
The low-pass filter smooths the phase detector output into a DC error voltage that steers the VCO frequency until it locks to the reference.
Which of the following best describes the function of a diplexer at an antenna connection?
Answer: It separates two frequency bands so they can share one antenna
A diplexer uses filters to route two different frequency bands to and from a shared antenna while isolating each port from the other.
What is the main advantage of a push-pull amplifier configuration over a single-ended amplifier?
Answer: Cancellation of even-order harmonic distortion
In push-pull circuits, the two transistors handle opposite half-cycles and their even-order distortion products cancel in the output transformer.
What happens to the Q factor of an LC resonant circuit when resistance is added in series with the inductor?
Answer: Q decreases because losses increase
Q = ωL/R, so increasing series resistance reduces Q, which broadens the resonance bandwidth and reduces selectivity.
In a superheterodyne receiver, what is the purpose of the image reject filter placed before the mixer?
Answer: To prevent a signal at the image frequency from entering the mixer
The image reject filter blocks signals at the image frequency (LO ± IF) that would otherwise mix down to the same IF as the desired signal, causing interference.
What is the effect of negative feedback on the output impedance of an amplifier?
Answer: It lowers output impedance, improving voltage regulation at the load
Negative voltage feedback reduces the amplifier's output impedance by a factor of (1 + Aβ), making the output behave more like an ideal voltage source.