What type of modulation occurs when the audio power for 100% modulation equals 50% of the DC input power to RF modulated amplifier?

What type of modulation occurs when the audio power for 100% modulation equals 50% of the DC input power to RF modulated amplifier?

• A. Grid
• B. Plate
• C. Cathode
• D. Anode

Answer: (B)

The modulation type described in the question is plate modulation, where the audio power for 100% modulation is effectively equal to 50% of the direct current (DC) input power to an RF modulated amplifier. In plate modulation, the audio signal varies the voltage applied to the plate (anode) of the amplifier tube, thereby affecting the power output. This method is commonly used in vacuum tube amplifiers, particularly in older radio transmitters. The key point here is that the audio signal impacts the plate voltage, allowing for efficient modulation of the radio frequency (RF) carrier signal. Because of this interaction, the power relationship specified—where audio power at full modulation is a significant fraction of the DC input power—accurately indicates plate modulation. Other modulation types, such as grid, cathode, or anode modulation, have different mechanisms and power relationships that do not fit the description provided in the question.

The modulation type described in the question is plate modulation, where the audio power for 100% modulation is effectively equal to 50% of the direct current (DC) input power to an RF modulated amplifier. In plate modulation, the audio signal varies the voltage applied to the plate (anode) of the amplifier tube, thereby affecting the power output.

This method is commonly used in vacuum tube amplifiers, particularly in older radio transmitters. The key point here is that the audio signal impacts the plate voltage, allowing for efficient modulation of the radio frequency (RF) carrier signal. Because of this interaction, the power relationship specified—where audio power at full modulation is a significant fraction of the DC input power—accurately indicates plate modulation.

Other modulation types, such as grid, cathode, or anode modulation, have different mechanisms and power relationships that do not fit the description provided in the question.