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E4C10

AMATEUR PRACTICES · 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

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What is an advantage of having a variety of receiver bandwidths from which to select?

  1. AThe noise figure of the RF amplifier can be adjusted to match the modulation type, thus increasing receiver sensitivity
  2. BReceiver power consumption can be reduced when wider bandwidth is not required
  3. CReceive bandwidth can be set to match the modulation bandwidth, maximizing signal-to-noise ratio and minimizing interference
  4. DMultiple frequencies can be received simultaneously if desired
Why Noise power reaching the detector is proportional to the receiver's bandwidth, so every extra hertz of passband beyond what the signal needs adds noise and lets in adjacent signals without adding any wanted energy. Setting the IF or DSP filter to roughly the modulation bandwidth (about 500 Hz or less for CW, 2.4 kHz for SSB, 6 to 15 kHz for FM) gives the best signal-to-noise ratio and rejects nearby QRM. Too narrow a filter, on the other hand, clips sidebands and distorts the signal, which is why a selection of bandwidths is useful.
Watch out Power consumption is irrelevant here, and noise figure is a property of the RF front end that filter selection does not change; likewise, a wide filter does not let you demodulate several signals at once in a conventional receiver.
Noise power rises with bandwidth: match the filter to the mode (CW 500 Hz, SSB 2.4 kHz, FM 6-15 kHz).
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of E4C

  1. E4C01 What is an effect of excessive phase noise in an SDR receiver's master clock oscillator?
  2. E4C02 Which of the following receiver circuits can be effective in eliminating interference from strong out-of-band…
  3. E4C03 What is the term for the suppression in an FM receiver of one signal by another stronger signal on the same f…
  4. E4C04 What is the noise figure of a receiver?
  5. E4C05 What does a receiver noise floor of -174 dBm represent?
  6. E4C06 How much does increasing a receiver's bandwidth from 50 Hz to 1,000 Hz increase the receiver's noise floor?
  7. E4C07 What does the MDS of a receiver represent?
  8. E4C08 An SDR receiver is overloaded when input signals exceed what level?
  9. E4C09 Which of the following choices is a good reason for selecting a high IF for a superheterodyne HF or VHF commu…
  10. E4C10 What is an advantage of having a variety of receiver bandwidths from which to select?
  11. E4C11 Why does input attenuation reduce receiver overload on the lower frequency HF bands with little or no impact …
  12. E4C12 How does a narrow-band roofing filter affect receiver performance?
  13. E4C13 What is reciprocal mixing?
  14. E4C14 What is the purpose of the receiver IF Shift control?
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