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E4D13

AMATEUR PRACTICES · Receiver performance characteristics: dynamic range; intermodulation and cross-modulation interference; third-order intercept; desensitization; preselector; sensitivity; link margin

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What is the received signal level with a transmit power of 10 W (+40 dBm), a transmit antenna gain of 6 dBi, a receive antenna gain of 3 dBi, and a path loss of 100 dB?

  1. A-51 dBm
  2. B-54 dBm
  3. C-57 dBm
  4. D-60 dBm
Why This is the basic link budget equation: received level in dBm equals transmit power in dBm plus all gains minus all losses. Here that is +40 dBm + 6 dBi + 3 dBi - 100 dB = -51 dBm. Because everything is already in decibel form, you just add and subtract; no multiplying is needed. Note that 10 W is +40 dBm, since 1 W is +30 dBm and each factor of 10 adds 10 dB.
Watch out The values near -54 dBm and -57 dBm come from leaving out one of the two antenna gains, and -60 dBm comes from ignoring both; every gain in the path counts, at each end.
Add gains, subtract losses, all in dB: 40 + 6 + 3 - 100 = -51. And remember 10 W = +40 dBm.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of E4D

  1. E4D01 What is meant by the blocking dynamic range of a receiver?
  2. E4D02 Which of the following describes problems caused by poor dynamic range in a receiver?
  3. E4D03 What creates intermodulation interference between two repeaters in close proximity?
  4. E4D04 Which of the following is used to reduce or eliminate intermodulation interference in a repeater caused by a …
  5. E4D06 What is the term for the reduction in receiver sensitivity caused by a strong signal near the received freque…
  6. E4D07 Which of the following reduces the likelihood of receiver desensitization?
  7. E4D08 What causes intermodulation in an electronic circuit?
  8. E4D09 What is the purpose of the preselector in a communications receiver?
  9. E4D10 What does a third-order intercept level of 40 dBm mean with respect to receiver performance?
  10. E4D11 Why are odd-order intermodulation products, created within a receiver, of particular interest compared to oth…
  11. E4D12 What is the link margin in a system with a transmit power level of 10 W (+40 dBm), a system antenna gain of 1…
  12. E4D13 What is the received signal level with a transmit power of 10 W (+40 dBm), a transmit antenna gain of 6 dBi, …
  13. E4D14 What power level does a receiver minimum discernible signal of -100 dBm represent?
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