Subelement A: — Topic :
Question 6A381
Element 6 (Radiotelegraph)What value of sinusoidal audio power is required to insure 100% modulation when the DC plate input toa modulated Class C amplifier has an efficiency of 60 % , and is 200 W?
Explanation
For 100% amplitude modulation (AM) using a plate-modulated Class C amplifier, the sinusoidal audio power supplied to the plate circuit must be equal to one-half of the DC input power to the modulated amplifier stage. This ensures that the peak audio voltage variation matches the DC plate voltage, causing the total instantaneous plate voltage to swing from zero to twice the DC supply, achieving full modulation.
Given the DC plate input power is 200 W:
Required Audio Power = 0.50 * DC Input Power
Required Audio Power = 0.50 * 200 W = 100 W.
The amplifier's efficiency (60%) is relevant for calculating the RF carrier output power (200 W * 0.60 = 120 W) but is not used to determine the audio power required for 100% plate modulation when the DC input power is known. Therefore, 100 W is the correct value.
Related Questions
6A38 A resistance across which a constant voltage is applied is doubled. What power dissipation will result?6A380 A plate choke in a Heising modulator:6A382 What would be the antenna current when a transmitter has an antenna current of 8 amp, under A -1, evenif it is 100% modulated by sinusoidal modulation?6A383 If a transmitter is adjusted for maximum power for telegraph, what must be done to be amplitudemodulated?6A384 A series-fed plate circuit of a vacuum tube amplifier has a short circuit of the plate bypass capacitor.What happened?