RF Signal Measurement, Noise, and TV/Radio System Components

Decibel (dB) Calculations and Conversions

The decibel (dB) is a logarithmic unit used to express the ratio of two values of a physical quantity, often power or voltage. It is widely used in electronics, acoustics, and control theory.

• Power Gain (GdB): 10 · log (Po / Pi)
• Voltage Gain (GdB): 20 · log (Vo / Vi)

Common dB Conversions:

• dBm to dBW: dBW = dBm - 30
• dBµV to dBm (75 Ohm): dBµV ≈ dBm + 107
• dBµV to dBW (75 Ohm): dBµV ≈ dBW + 137

Note: Specific conversion values like +108.8 dB and +138.8 dB may apply to particular system impedances or standards.

Understanding Noise in Signal Systems

Noise refers to any unwanted signal that accompanies a useful signal, degrading its quality.

Types of Noise:

• External Noise: Originates from sources outside the desired signal path.
  • Examples: Galactic radio emission, atmospheric noise (e.g., lightning), human-made interference (e.g., electrical devices).
• Internal Noise: Generated within the receiving system components.
  • Examples: Thermal noise (from resistors), antenna noise, semiconductor device noise.

Signal Quality Metrics

• Carrier-to-Noise Ratio (C/N)

  The relationship between the level of the carrier signal (Si) and the noise level (Ni) at a specific point in the system.

  • Linear Scale: C / N = Si / Ni
  • Decibel Scale: C / N = 10 · log (Si / Ni)

  A poor C/N ratio results in a bad image on the screen, often visible as "snow" or pixelation.

• Signal-to-Noise Ratio (S/N)

  The relationship between the level of the baseband signal and the noise level at a point in the system, commonly used in analog TV.

• Bit Error Rate (BER)

  The number of bit errors per unit time, or the fraction of bits that are erroneous over a given time interval.

• Energy per Bit to Noise Power Spectral Density Ratio (Eb/No)

  The ratio of energy per bit to the noise power spectral density, a key parameter in digital communication system performance.

Television and Radio Signal Systems

Signal Sensor System

A set of elements responsible for receiving broadcast signals from terrestrial and satellite television and radio transmissions.

• Components: TV antenna, FM and DAB radio antennas, mast, towers, preamplifiers.

Signal Processing System (Headend Equipment)

A set of elements responsible for processing and preparing signals from the sensor system for distribution.

• Components: Amplifiers, Mixers, Filters, Power Supplies, Attenuators, Equalizers, Modulators.

Distribution Network

The part of the installation responsible for distributing the processed TV signal from the headend equipment to the users.

• Components: Splitters, Taps (Directional Couplers), User Outlets.

Distribution Network Components

• Splitters

  A passive device that divides an input signal into two or more output signals of equal power, distributing them to different paths.

• Taps (Directional Couplers)

  A device that diverts a portion of the input signal to one or more outputs (taps), allowing the remaining signal to pass through to other parts of the distribution network.

• User Outlets (Wall Outlets)

  A device where the user connects terminal equipment (e.g., TV, radio) to access TV and radio services. These can be through-type or end-of-line outlets.

Coaxial Cable Connectors

• BNC Connector

  A bayonet-style metal fitting primarily used with measurement equipment, such as oscilloscopes, and in professional video applications.

• IEC Connector (Coaxial)

  A common accessory connection that allows for quick connection of a coaxial cable to a device, widely used for terrestrial TV and radio in Europe.

• F Connector

  A threaded accessory connection that allows for quick and secure connection of a coaxial cable to a device, commonly used for satellite TV and cable TV.

User Internal Network Topologies

Common configurations for distributing signals within a user's premises:

• Serial Topology: Devices are connected in a chain.
• Star Topology: All devices connect to a central point.