Understanding TV Antenna Systems: A Comprehensive Guide

Posted on May 4, 2024 in Technology

Types of TV Antenna Systems

Single-Family vs. Collective Buildings

TV antenna systems cater to two primary types of structures: single-family houses and collective buildings (buildings with multiple users).

Components of a TV Antenna System

Header Equipment

The header equipment receives signals from sensors and systems, ensuring their proper distribution to users. It houses all active components of the installation and is typically located near the sensor signals within the building.

Distribution Network

The distribution network carries the signal from the header equipment to the user outlets. It comprises coaxial cables, connectors, distributors, and bypass taps.

Terrestrial Antennas

Terrestrial antennas facilitate the transmission of power between the radiated power and the power tour.

Types of Reception Antennas

  • Dipole Antenna: Consists of two straight conductors of equal length, placed side by side, with an impedance of 75 ohms (300 ohms for a folded dipole).
  • Folded Dipole: Created by bending a dipole antenna.
  • Yagi Antenna: Composed of:
    • Bent dipole
    • Directors: Enhance gain and directivity towards the IA, focusing the signal on the dipole.
    • Reflectors: Can be single or double, reflecting the signal towards the front. Maximum transparency is achieved when Z1 = Za.

Key Antenna Parameters

  • Directivity: An antenna’s ability to concentrate radiated power in a specific direction. The antenna is pointed in the direction of maximum efficiency.
  • Gain: Quantifies the relationship between input and radiated or received power by a directive antenna in the direction of maximum transmission/reception.
  • Beamwidth: The angle formed by two imaginary lines intersecting the radioacio diagram at points where the gain is 3 dB less than the maximum value.
  • Bandwidth: Allows for efficient and reliable capture of frequencies near the working frequency. For example, a 10MHz bandwidth would cover frequencies from 365MHz to 375MHz.

TV Bands and Channels

A TV channel consists of a composite image (amplitude modulated) and sound (frequency modulated).

Antenna Orientation

Proper antenna orientation is crucial for optimal reception. Consider the following factors:

  • Placement in a location with minimal obstacles.
  • Orientation towards the central transmitter or re-transmitter.
  • Accessibility of the site.
  • Distances between antennas (3m side and 1m height).

Preamplifiers

Preamplifiers boost the signal level near the antenna with minimal noise addition, enabling further processing by other components. They are particularly useful when the antenna output signal is weak or has a poor Signal-to-Noise Ratio.

Amplifiers

Amplifiers increase the level of existing signals, resulting in a higher output level compared to the input. Key characteristics include:

  • Gain: Measured in dB, representing the difference between input and output levels.
  • Noise Figure: Expressed in dBi, indicating the maximum undistorted output level the amplifier can deliver.

Types of Amplifiers

  • Single-Channel Amplifiers: Amplify a single TV channel while removing the rest. They are used in systems with automatic channel separation at the input and automatic channel mixing at the output. These amplifiers are employed for weak signals due to their high gain. Most models are CAG, and some offer voltage step switching towards the antenna.
  • Mast Amplifiers: Used in single-dwelling installations where the required output voltage level is not very high due to the limited number of outlets.
  • Central Amplifiers: Employed in collective installations and located inside the building. They can have multiple inputs and may include built-in filters for step rejection.
  • Bandwidth Amplifiers: Amplify one or more bands. There are two types:
    • Joint amplification or broadband amplification: Amplifies all bands in a single chip.
    • Broadband amplification with separate amplification: Allows for tuning bands when the number of channels increases on one side but not the other.
  • Multichannel Amplifier: Amplifies a group of 4 digital channels, typically from C/66 to C/69.

Example: The Micromatv pro 300 is an amplifier with filters that can amplify up to five channels.

Shunt

A shunt distributes the signal vertically throughout the various floors of a building, delivering it to different apartments and ensuring balance between outlets within each floor.

Distributors

Distributors split the signal traveling over the network into two or more networks with minimal impact. Induction distributors are the most common type.

User Outlets

User outlets provide an acceptable signal level (57-80 dB) for TV viewing.

Advantages of Single-Channel Systems

  • Higher output levels.
  • Increased number of incorporated channels.
  • Possibility of reducing amplifiers.
  • If a module fails, only that module is affected.
  • Utilization of bypass distribution systems in collective installations.
  • Channel-to-channel tuning capability.