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E4C09

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

E4C09E4C →

Which of the following choices is a good reason for selecting a high IF for a superheterodyne HF or VHF communications receiver?

  1. AFewer components in the receiver
  2. BReduced drift
  3. CEasier for front-end circuitry to eliminate image responses
  4. DImproved receiver noise figure
Why In a superheterodyne receiver the image frequency sits 2 x IF away from the desired signal. Raising the IF pushes that image further from the wanted frequency, so the relatively broad front-end preselector filter can attenuate it much more easily. That is why many HF and VHF designs up-convert to an IF above the tuning range, for example 45 MHz or 70 MHz, before down-converting to a lower IF for selectivity.
Watch out A high IF actually tends to make narrow-bandwidth crystal filtering harder and does nothing for oscillator drift; drift and tight selectivity are the arguments for a low IF, which is why dual-conversion designs use both.
Image = desired +/- 2 x IF. Bigger IF, farther image, easier to filter out.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
← E4C08 All of E4C E4C10 →

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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