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E4B06

AMATEUR PRACTICES · Measurement technique and limitations: instrument accuracy and performance limitations; probes; techniques to minimize errors; measurement of Q; instrument calibration; S parameters; vector network analyzers; RF signals

E4B06E4B →

How much power is being absorbed by the load when a directional power meter connected between a transmitter and a terminating load reads 100 watts forward power and 25 watts reflected power?

  1. A100 watts
  2. B125 watts
  3. C112.5 watts
  4. D75 watts
Why A directional wattmeter measures forward and reflected power separately. The net power actually delivered to and absorbed by the load is the forward power minus the reflected power, so 100 W - 25 W = 75 W. The reflected 25 W travels back toward the transmitter rather than being dissipated in the load.
Watch out The choice of 125 watts comes from adding the two readings, but reflected power is not additional power delivered; it is power returning from the load. The 100 watt choice ignores the reflection entirely.
Net power = forward minus reflected. Subtract, never add.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of E4B

  1. E4B01 Which of the following factors most affects the accuracy of a frequency counter?
  2. E4B02 What is the significance of voltmeter sensitivity expressed in ohms per volt?
  3. E4B03 Which S parameter is equivalent to forward gain?
  4. E4B04 Which S parameter represents input port return loss or reflection coefficient (equivalent to VSWR)?
  5. E4B05 What three test loads are used to calibrate an RF vector network analyzer?
  6. E4B06 How much power is being absorbed by the load when a directional power meter connected between a transmitter a…
  7. E4B07 What do the subscripts of S parameters represent?
  8. E4B08 Which of the following can be used to determine the Q of a series-tuned circuit?
  9. E4B09 Which of the following can be measured by a two-port vector network analyzer?
  10. E4B10 Which of the following methods measures intermodulation distortion in an SSB transmitter?
  11. E4B11 Which of the following can be measured with a vector network analyzer?
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