finals Flashcards
(48 cards)
What happens to capacitive reactance as the frequency of operation increases?
decrease
As frequency decreases, how does the reactance of a coil vary?
decrease
What is skin effect, and how does it affect the Q of a coil?
Skin effect is a high-frequency phenomenon where current tends to flow near the surface of a conductor, increasing its effective resistance. This higher resistance lowers the Q (quality factor) of a coil, as Q is inversely proportional to resistance
What happens to a wire when a ferrite bead is placed around it?
A ferrite bead acts like a high-frequency resistor. It adds inductive impedance and loss to suppress high-frequency noise or EMI, effectively filtering unwanted signals
What is the name given to the widely used coil form that is shaped like a doughnut?
toroid. Toroids help contain magnetic fields and reduce interference
Describe the current and impedance in a series RLC circuit at resonance.
At resonance, the inductive and capacitive reactances cancel ( XL = XC), and the impedance is purely resistive and at a minimum. The current is at its maximum value.
Describe the current and impedance in a parallel RLC circuit at resonance.
In a parallel RLC circuit, resonance results in maximum impedance. The current drawn from the source is minimum, although large circulating currents may exist between the coil and capacitor
State in your own words the relationship between Q and the bandwidth of a tuned circuit.
Q is inversely proportional to bandwidth. A high Q means narrow bandwidth and better frequency selectivity.
What kind of filter is used to select a single signal frequency from many signals?
A band-pass filter is used to isolate and pass a specific signal frequency while attenuating others.
What kind of filter would you use to get rid of an annoying 120-Hz hum?
A notch filter or band-stop filter tuned to 120 Hz is used to eliminate the unwanted hum.
What does selectivity mean?
Selectivity is the circuit’s ability to discriminate between closely spaced frequencies, allowing only the desired one to pass while rejecting others.
State the Fourier theory in your own words.
Fourier theory states that any complex periodic waveform can be broken down into a sum of sine and cosine waves (harmonics) with different frequencies and amplitudes.
Define the terms time domain and frequency domain.
Time domain: How a signal varies over time (e.g., waveform).
Frequency domain: The signal represented by its frequency components.
Write the first four odd harmonics of 800 Hz.
800 Hz (1st)
2400 Hz (3rd)
4000 Hz (5th)
5600 Hz (7th)
What waveform is made up of even harmonics only? What waveform is made up of odd harmonics only?
Even harmonics: Full-wave rectified sine wave
Odd harmonics: Square wave, triangular wave
Why is a nonsinusoidal signal distorted when it passes through a filter?
Nonsinusoidal signals contain multiple harmonics. A filter may attenuate some of these harmonics, altering the original shape, thus causing distortion.
Explain how capacitance and inductance can exist in a circuit without lumped capacitors and inductor components being present.
Capacitance and inductance can exist inherently in circuit wires, traces, and layouts due to their physical properties. Two conductors separated by an insulator create a parasitic capacitance, and any current-carrying conductor can create a magnetic field, forming parasitic inductance.
Define modulation:
Modulation is the process of varying a carrier signal in proportion to an information (baseband) signal in order to transmit it more effectively over a medium
True or false? The carrier frequency remains constant during AM:
True. Only the amplitude changes in AM
What is the modulation index called when it is expressed as a percentage?
Percentage of modulation
How can the voltage across the coil or capacitor in a series resonant circuit be greater than the source voltage at resonance?
At resonance, the reactive elements (L and C) can each develop high voltages due to the high circulating current in the loop, even though the total voltage across the series circuit equals the source. This is known as resonant rise.
What type of filter would you use to prevent the harmonics generated by a transmitter from reaching the antenna?
A low-pass filter (LPF) is typically used. It allows the fundamental frequency to pass but attenuates higher-frequency harmonics.
What kind of filter would you use on a TV set to prevent a signal from a CB radio on 27 MHz from interfering with a TV signal on channel 2 at 54 MHz?
A high-pass filter (HPF) with a cutoff frequency just above 27 MHz can block the CB signal while allowing the TV signal at 54 MHz to pass.
Explain why it is possible to reduce the effective Q of a parallel resonant circuit by connecting a resistor in parallel with it.
Adding a resistor in parallel increases the overall losses in the circuit. Since Q is inversely proportional to resistance in a parallel resonant circuit, this lowers the Q, reducing selectivity and increasing bandwidth
