Chapter 2: AM

Combining the low frequency signal with very high frequency radio wave is called

• modulation

• demodulation

• coding

• superimposition

Identify the type of modulation where the modulating wave is superimposed on a high-frequency carrier wave.

• Phase modulation

• Amplitude modulation

• Frequency modulation

• Wavelength modulation

Answer explanation

In Amplitude modulation, the modulating wave is superimposed on a high-frequency carrier wave such that the amplitude of the modulated wave varies as the amplitude of the modulating wave. The frequency of the modulated wave is equal to the frequency of the carrier wave.

Which of the following is true about carrier signal?

• Carrier signals have low frequency

• Carrier signals are used to increase the wavelength of the signal

• Carrier signals have high frequency

• Carrier signals and message signals are the same

Answer explanation

Carrier signals have high frequencies and hence are used in the transmission of radio waves.

Which one of the following is the process of recovering the modulated signal?

• Amplification

• Detection

• Attenuation

• Transmission

Answer explanation

Detection is the process of recovering the modulating signal from the modulated carrier wave.

Which among the following can be detected by an envelope detector?

• Low frequency AM waves

• Very low frequency AM waves

• Envelope detectors cannot detect AM waves

• High frequency AM waves

Answer explanation

An envelope detector is used to detect high-frequency amplitude modulated (AM) waves. It takes high-level AM waves as input and then provides an output that can be considered as an envelope of the original signal. An envelope detector may consist of a simple RC circuit.

What happens when the amplitude of the modulating signal is greater than the amplitude of the carrier?

• Decay

• Distortion

• Amplification

• Attenuation

Answer explanation

The zero reference line of the modulating signal coincides with the peak value of the unmodulated carrier. Because of this, the relative amplitudes of the carrier and modulating signal are important. When the amplitude of the modulating signal is greater than the amplitude of the carrier, distortion will occur.

What is the circuit used for producing AM called?

• Modulator

• Transmitter

• Receiver

• Duplexer

Answer explanation

The circuit used for producing AM is called a modulator. It has two inputs, the carrier and the modulating signal, and the resulting output is the modulated signal. Amplitude modulators compute the product of the carrier and modulating signals.

The ratio between the modulating signal voltage and the carrier voltage is called?

• Amplitude modulation

• Modulation frequency

• Modulation index

• Ratio of modulation

Answer explanation

modulation index m, is the ratio m = ^V_m⁄_Vc.

What is the condition for greatest output power at the transmitter without distortion?

• Modulating signal voltage > Carrier voltage

• Modulating signal voltage < Carrier voltage

• Modulating signal voltage = Carrier voltage

• Modulating signal voltage = 0

Answer explanation

When the modulation index is 1 or the percentage of modulation is 100, modulating signal voltage is equal to the carrier voltage. This results in the greatest output power at the transmitter and the greatest output voltage at the receiver, with no distortion.

What is the wave of frequency that occurs at the sum and difference of the carrier and modulating signal is called?

• Noise signals

• Sideband

• Extraband

• Neutral band

Answer explanation

New signals at different frequencies are formed when an intelligence signal is modulated with a carrier. These signals are called sidebands and usually have the frequency of the sum and the difference of the carrier and the modulating signal.