GROL Filters and Frequency Control 1 — Questions and Answers
Question 1: What is the primary function of a low-pass filter in a radio transmitter?
- To pass all frequencies equally
- To pass frequencies below a cutoff frequency while attenuating higher frequencies (Correct answer)
- To pass only a narrow band of frequencies
- To pass frequencies above a cutoff frequency only
Correct answer: To pass frequencies below a cutoff frequency while attenuating higher frequencies
A low-pass filter allows signals below its cutoff frequency to pass while attenuating signals above that frequency, commonly used to suppress harmonics.
Question 2: Which type of filter passes a specific band of frequencies while attenuating frequencies both above and below that band?
- Low-pass filter
- High-pass filter
- Band-pass filter (Correct answer)
- Band-stop filter
Correct answer: Band-pass filter
A band-pass filter has both a lower and upper cutoff frequency, allowing only the frequencies between them to pass through.
Question 3: What type of crystal is most commonly used in oscillators and filters for precise frequency control?
- Sapphire
- Quartz (Correct answer)
- Ruby
- Tourmaline
Correct answer: Quartz
Quartz crystals exhibit the piezoelectric effect and have extremely stable resonant frequencies, making them ideal for precise frequency control.
Question 4: What is the Q factor of a filter or resonant circuit?
- The ratio of reactive power to real power dissipated
- The ratio of resonant frequency to bandwidth (Correct answer)
- The ratio of capacitance to inductance
- The ratio of output power to input power
Correct answer: The ratio of resonant frequency to bandwidth
Q (quality factor) is defined as the resonant frequency divided by the 3 dB bandwidth, with higher Q indicating a sharper, more selective filter.
Question 5: In a series LC circuit at resonance, what is the impedance?
- Maximum impedance
- Minimum impedance (approaches zero) (Correct answer)
- Equal to the capacitive reactance alone
- Equal to the inductive reactance alone
Correct answer: Minimum impedance (approaches zero)
At resonance in a series LC circuit, the inductive and capacitive reactances cancel each other, leaving only the small series resistance, resulting in minimum impedance.
Question 6: What is the purpose of a notch (band-stop) filter?
- To amplify a specific frequency
- To pass all frequencies
- To sharply attenuate a specific frequency or narrow band (Correct answer)
- To convert AC to DC
Correct answer: To sharply attenuate a specific frequency or narrow band
A notch or band-stop filter is designed to reject a specific frequency or narrow frequency band while passing all others, often used to eliminate interference.
GROL Filters and Frequency Control 1
What is the primary function of a low-pass filter in a radio transmitter?