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
When using a field-effect transistor (FET) as an RF amplifier, what is the advantage of its high input impedance?
Answer: It minimizes loading of the signal source or preceding stage
A high input impedance prevents the FET gate from loading down the signal source, preserving signal amplitude and avoiding bandwidth degradation.
What is the function of a limiter stage in an FM receiver's IF chain?
Answer: To remove amplitude variations before the discriminator
The limiter clips amplitude variations from the IF signal so the discriminator only responds to frequency changes, rejecting AM noise and interference.
In a crystal-controlled oscillator, what determines the operating frequency?
Answer: The mechanical resonance of the quartz crystal
The piezoelectric quartz crystal's mechanical resonant frequency determines the oscillation frequency with very high stability.
What effect does increasing the emitter resistor value have in a BJT common-emitter amplifier without a bypass capacitor?
Answer: Gain decreases and stability increases
An unbypassed emitter resistor applies negative feedback, reducing voltage gain but improving linearity and thermal stability.
Which type of amplifier class is most efficient for RF power amplifiers transmitting constant-envelope signals such as FM?
Answer: Class C
Class C amplifiers can exceed 80% efficiency by conducting for less than half a cycle, and the tank circuit restores the full waveform for constant-envelope signals.
What is the primary cause of intermodulation distortion (IMD) in an amplifier?
Answer: Nonlinear transfer characteristics of the active device
Nonlinearities in the amplifier's transfer function cause input signals to mix, producing sum and difference frequency products known as intermodulation products.
A toroid core is preferred over an air-core inductor for HF applications primarily because it:
Answer: Confines the magnetic field internally, reducing radiation and coupling
The closed magnetic path of a toroid core concentrates flux inside the core, minimizing stray coupling to nearby components and reducing EMI.