Electromagnetic Waves, Bands, and Channels in Television

Posted on Feb 17, 2025 in Electronics

Electromagnetic Waves and Their Properties

Calculating Frequency and Wavelength

1. If an electromagnetic wave has a repetition period of 5 microseconds, what is its frequency and wavelength?

Solution: Period and frequency are inversely related. Frequency (F) can be calculated using the formula: F = 1/T = 1/(5 * 10-6) = 200,000 Hz. From the frequency, the wavelength (λ) is calculated: λ = c/F = (3 * 108) / (2 * 105) = 1500 m.

2. If an electromagnetic wave has a wavelength of 10 km, what is its frequency and period?

Solution: Frequency is calculated from wavelength: F = c/λ = (3 * 108) / (10 * 103) = 30 kHz. The period (T) is the inverse of the frequency: T = 1/F = 1/(3 * 104) = 33.3 μs.

Key Concepts in Signal Transmission

1. Define the following concepts:

  • a) Generic Band: Internationally established spectrum divisions based on signal frequency and wavelength.
  • b) Specific Band: A precisely defined spectrum area with frequencies used for a particular type of communication.
  • c) Channel: Frequencies reserved for each communication within a specific band.
  • d) Polarization: The arrangement of electric and magnetic fields during propagation.
    • Linear Polarization: The field orientation remains constant. Can be vertical or horizontal.
    • Circular Polarization: The field rotates around the propagation direction. Can be left (clockwise) or right-handed (counterclockwise).

Terrestrial Television Bands and Channels

6. What are the limits of terrestrial television in Band IV and Band V, and the channels comprising each band?

Band IV: 470 MHz to 606 MHz (Channels 21-37)
Band V: 606 MHz to 790 MHz (Channels 38-60)

Channel Width and its Implications

8. Discuss the differences in channel width:

  • In AM commercial radio, a single low-quality voice channel is transmitted with a width of 9 kHz.
  • Analog terrestrial television channels are 8 MHz wide to transmit image, high-quality sound, and data simultaneously.
  • Digital terrestrial television, using different modulation and signal processing, can transmit up to five TV services simultaneously in an 8 MHz channel.

Analyzing a TV Channel Display

10. Analyze the picture (not provided) and answer the following:

a) How many TV channels appear? 4 channels.

b) What kind are they? 2 digital and 2 analog.

c) What band do they belong to? UHF, Generic Band V.

d) What radio frequency channels do they occupy? Channels 39, 44, 45, and 49.

Reallocation of Television Frequencies

5. What happened to channels 61-69 (790-862 MHz) of Band V TV since 2014?

These channels have been reallocated for 4G/LTE mobile phone signals.

BLV and DBL Modulation in Analog TV

What is the difference between BLV and DBL, and what type of modulation do they correspond to?

Both are variants of Amplitude Modulation (AM) used in analog TV. BLV modulates the image and uses a filter to partially clip one sideband, saving bandwidth. DBL carries color information and suppresses the carrier to save energy and reduce interference.