Extra-Study/pages/E4C.md

E4C Receiver performance: phase noise, noise floor, image rejection, minimum detectable signal (MDS), increasing signal-to-noise ratio and dynamic range, noise figure, reciprocal mixing; selectivity; SDR non-linearity; use of attenuators at low frequencies

• E4C01 (D) What is an effect of excessive phase noise in an SDR receiver’s master clock oscillator? #card
  • A. It limits the receiver’s ability to receive strong signals
  • B. It can affect the receiver’s frequency calibration
  • C. It decreases the receiver’s third-order intercept point
  • D. It can combine with strong signals on nearby frequencies to generate interference
• E4C02 (A) Which of the following receiver circuits can be effective in eliminating interference from strong out-of-band signals? #card
  • A. A front-end filter or preselector
  • B. A narrow IF filter
  • C. A notch filter
  • D. A properly adjusted product detector
• E4C03 (C) What is the term for the suppression in an FM receiver of one signal by another stronger signal on the same frequency? #card
  • A. Desensitization
  • B. Cross-modulation interference
  • C. Capture effect
  • D. Frequency discrimination
• E4C04 (D) What is the noise figure of a receiver? #card
  • A. The ratio of atmospheric noise to phase noise
  • B. The ratio of the noise bandwidth in hertz to the theoretical bandwidth of a resistive network
  • C. The ratio in dB of the noise generated in the receiver to atmospheric noise
  • D. The ratio in dB of the noise generated by the receiver to the theoretical minimum noise
• E4C05 (B) What does a receiver noise floor of -174 dBm represent? #card
  • A. The receiver noise is 6 dB above the theoretical minimum
  • B. The theoretical noise in a 1 Hz bandwidth at the input of a perfect receiver at room temperature
  • C. The noise figure of a 1 Hz bandwidth receiver
  • D. The receiver noise is 3 dB above theoretical minimum
• E4C06 (D) How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor? #card
  • A. 3 dB
  • B. 5 dB
  • C. 10 dB
  • D. 13 dB
• E4C07 (B) What does the MDS of a receiver represent? #card
  • A. The meter display sensitivity
  • B. The minimum discernible signal
  • C. The modulation distortion specification
  • D. The maximum detectable spectrum
• E4C08 (D) An SDR receiver is overloaded when input signals exceed what level? #card
  • A. One-half of the maximum sample rate
  • B. One-half of the maximum sampling buffer size
  • C. The maximum count value of the analog-to-digital converter
  • D. The reference voltage of the analog-to-digital converter
• E4C09 (C) Which of the following choices is a good reason for selecting a high IF for a superheterodyne HF or VHF communications receiver? #card
  • A. Fewer components in the receiver
  • B. Reduced drift
  • C. Easier for front-end circuitry to eliminate image responses
  • D. Improved receiver noise figure
• E4C10 (C) What is an advantage of having a variety of receiver bandwidths from which to select? #card
  • A. The noise figure of the RF amplifier can be adjusted to match the modulation type, thus increasing receiver sensitivity
  • B. Receiver power consumption can be reduced when wider bandwidth is not required
  • C. Receive bandwidth can be set to match the modulation bandwidth, maximizing signal-to-noise ratio and minimizing interference
  • D. Multiple frequencies can be received simultaneously if desired
• E4C11 (D) Why does input attenuation reduce receiver overload on the lower frequency HF bands with little or no impact on signal-to-noise ratio? #card
  • A. The attenuator has a low-pass filter to increase the strength of lower frequency signals
  • B. The attenuator has a noise filter to suppress interference
  • C. Signals are attenuated separately from the noise
  • D. Atmospheric noise is generally greater than internally generated noise even after attenuation
• E4C12 (C) How does a narrow-band roofing filter affect receiver performance? #card
  • A. It improves sensitivity by reducing front-end noise
  • B. It improves intelligibility by using low Q circuitry to reduce ringing
  • C. It improves blocking dynamic range by attenuating strong signals near the receive frequency
  • D. All these choices are correct
• E4C13 (D) What is reciprocal mixing? #card
  • A. Two out-of-band signals mixing to generate an in-band spurious signal
  • B. In-phase signals cancelling in a mixer resulting in loss of receiver sensitivity
  • C. Two digital signals combining from alternate time slots
  • D. Local oscillator phase noise mixing with adjacent strong signals to create interference to desired signals
• E4C14 (C) What is the purpose of the receiver IF Shift control? #card
  • A. To permit listening on a different frequency from the transmitting frequency
  • B. To change frequency rapidly
  • C. To reduce interference from stations transmitting on adjacent frequencies
  • D. To tune in stations slightly off frequency without changing the transmit frequency