Practical Circuits and Components 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 Circuits and Components flashcards as text
In a Colpitts oscillator, what elements form the feedback voltage divider?
Answer: Two capacitors in series across the tank inductor
The Colpitts oscillator uses a capacitive voltage divider (two capacitors in series) tapped across the tank inductor to feed back the correct phase and amplitude.
What is the significance of the '1 dB compression point' specification for an RF amplifier?
Answer: The output power level where gain has dropped 1 dB below the linear gain value due to saturation
The 1 dB compression point marks the onset of significant non-linearity — above this level, gain compresses and distortion products increase rapidly.
Why is a low-pass filter connected between a transmitter and its antenna?
Answer: To attenuate harmonic and spurious emissions that could interfere with other services
Low-pass filters suppress harmonics and other spurious signals above the transmit frequency, keeping the transmitted spectrum within FCC limits.
What happens to the resonant frequency of an LC tank circuit if the inductor core is partially removed?
Answer: Resonant frequency increases because inductance decreases
Removing core material reduces the effective permeability, lowering inductance; since f = 1/(2π√LC), lower L raises the resonant frequency.
A cascode amplifier consists of what transistor configuration?
Answer: A common-emitter stage driving a common-base stage
The cascode pairs a common-emitter (or common-source) input with a common-base (common-gate) output, reducing the Miller effect and extending bandwidth while maintaining gain.
What is the primary purpose of a step-start or soft-start circuit in an HF linear amplifier power supply?
Answer: To limit inrush current through filter capacitors when power is first applied, protecting rectifiers and fuses
Large filter capacitors draw a very high inrush current when uncharged; a step-start circuit inserts a series resistor initially then bypasses it, limiting stress on components.
Which semiconductor device exhibits negative resistance and is used in microwave oscillator circuits?
Answer: Gunn diode
The Gunn diode exhibits negative resistance due to the transferred-electron effect in gallium arsenide, sustaining oscillations in microwave resonant cavities.