Understanding Modulation in TV Telecasting

Telecasting television (TV) programs involves transmitting both video (picture) and audio (sound) signals wirelessly. For this transmission, these signals need to be modulated onto carrier waves. Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulation signal (like the audio or video signal) to transmit information.

The question asks about the types of modulation used specifically for telecasting TV programs from the given options:

• (i) Amplitude modulation (AM)
• (ii) Frequency modulation (FM)
• (iii) Phase modulation (PM)
• (iv) Pulse modulation

Modulation for TV Signals

In standard analog television broadcasting, different modulation techniques are used for the video and audio components:

• Video Signal: The video information (the picture) is typically transmitted using Amplitude Modulation (AM). Specifically, a variation called Vestigial Sideband Modulation (VSB), which is a form of AM, is often used because it is more efficient in terms of bandwidth compared to standard double-sideband AM while still being relatively simple to demodulate. However, fundamentally, it is based on varying the amplitude of the carrier wave according to the video signal.
• Audio Signal: The audio information (the sound) that accompanies the video is typically transmitted using Frequency Modulation (FM). FM is generally less susceptible to noise and interference compared to AM, which provides a better sound quality for the audio part of the broadcast.

Let's consider the other options:

• (iii) Phase modulation (PM): While PM is related to FM (both are types of angle modulation), standard analog TV audio broadcasting uses FM. PM is not the primary modulation type specified for this purpose.
• (iv) Pulse modulation: Pulse modulation techniques (like Pulse Amplitude Modulation - PAM, Pulse Width Modulation - PWM, Pulse Position Modulation - PPM, or Pulse Code Modulation - PCM) are typically associated with digital signal transmission. While modern digital TV broadcasting (like DVB or ATSC) uses complex digital modulation schemes that might involve aspects related to pulse techniques (especially PCM within the digital signal chain), the question likely refers to the fundamental modulation types used in the broadcast itself, which for traditional or foundational understanding relates to analog TV where AM and FM are key. Pulse modulation isn't the direct method applied to the RF carrier for analog TV.

Based on the standard modulation types used for analog TV broadcasting, the video component uses Amplitude Modulation (AM) and the audio component uses Frequency Modulation (FM).

Therefore, the types of modulation used for telecasting TV programs are Amplitude modulation (i) and Frequency modulation (ii).