9. In TV, an electrical disturbance (noise) affects
neither the video nor the audio signals
only the audio signals
both the video and audio signals
only the video signals
Answer.4. only the video signals
In TV transmission:
A video is Vestigial sideband modulated, which is a type of amplitude-modulated waveform
The Video signals are thus encoded in amplitude variations of the carriers
The Audio signal is encoded in FM waveform
Thus, the audio signals are encoded as frequency variations of the carrier
Noise is the signal that affects amplitude majorly. Thus, the video signal is distorted from amplitude variations.
10. A signal contains components at 400 Hz and 2400 Hz This signal modulates a carrier of frequency 100 MHz. However, after demodulation, it is found that the 400 Hz signal component is present. The channel bandwidth is 15 kHz. What is the reason for the higher frequency signal not being detected properly?
Modulation used in FM and BW is insufficient
Modulation used in AM and BW is insufficient
Modulation used in FM but pre-emphasis is not used
Modulation used in AM but detector is for FM
Answer.3. Modulation used in FM but pre-emphasis is not used
In FM broadcasting, pre-emphasis improvement is the improvement in the signal-to-noise ratio of the high-frequency portion of the baseband. The higher frequency signal is not to be detected properly because modulation is used in FM but pre-emphasis is not used.
In the process of detecting a frequency modulated signal, the receiver produces a noise spectrum that rises in frequency (a so-called triangular spectrum). This is the reason why a preemphasis is required. Without pre-emphasis, the received audio would sound unacceptably noisy at high frequencies, especially under conditions of low carrier-to-noise ratio, i.e., during fringe reception conditions. Preemphasis increases the magnitude of the higher signal frequencies, thereby improving the signal-to-noise ratio.