Question
What signal source is connected to the vertical input of an oscilloscope when checking the RF envelope pattern of a transmitted signal?
Answer Options
- A) The local oscillator of the transmitter
- B) An external RF oscillator
- C) The transmitter balanced mixer output
- D) The attenuated RF output of the transmitter
Correct Answer: D
Explanation
To check the RF envelope pattern of a transmitted signal (such as for key clicks on CW or flat-topping on SSB), the oscilloscope needs to display the actual output signal’s amplitude over time. Since a transmitter’s output power can damage the sensitive input circuitry of an oscilloscope, the signal must first be reduced in voltage.
Therefore, the signal connected to the vertical input of the oscilloscope must be the attenuated RF output of the transmitter. This is typically accomplished using a resistive dummy load with a small sampling probe or a special RF pickup device that safely reduces the RF voltage to a level the oscilloscope can handle.
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