Signal Strength

Signal strength is the measurable magnitude of an electrical signal as it travels through a medium—such as air, copper wire, or fiber optic cable. It is a foundational concept in electronics, telecommunications, broadcasting, networking, and aviation. Signal strength directly determines the reliability, quality, and reach of any communication system, from Wi-Fi and cellular networks to satellite links, radio stations, cable TV, and air traffic control.

Understanding Signal Strength

Signal strength typically refers to the power or amplitude of a signal, measured at a specific point in the transmission path. In wireless and RF applications, it is most often expressed in decibels relative to a reference power (dBm or dBW). In cable and broadband systems, it may be expressed in dBmV (decibels relative to 1 millivolt) or dBμV (relative to 1 microvolt).

Why is signal strength important?

• It affects the clarity, speed, and reliability of data, voice, and video transmission.
• Weak signal strength can cause dropped calls, slow data, poor video quality, or total communication failure.
• Excessively strong signals can cause distortion, equipment overload, or interference with other systems.

Maintaining optimal signal strength is critical for system design, troubleshooting, regulatory compliance, and user satisfaction.

Amplitude: The Foundation of Signal Strength

Amplitude is the maximum extent of a signal’s oscillation, measured from its average value. In AC and RF systems, it can be characterized as:

• Peak amplitude (Aₚₑₐₖ): Maximum value above zero.
• Peak-to-peak amplitude (Aₚ₋ₚ): Vertical distance between max positive and max negative values.
• Root Mean Square (RMS) amplitude (Aᵣₘₛ): Effective value for power calculations, especially for sine waves.

Amplitude determines how much energy a signal carries. In communication systems, amplitude affects the system’s sensitivity and its ability to distinguish the signal from noise.

Power: The Driving Force

Power is the rate at which electrical energy is transferred or converted. In signal transmission, power is crucial for determining how far a signal can travel and how well it can be received.

• Power (Watts): P = V² / R or P = I² × R or P = V × I, where V = voltage, I = current, R = resistance.
• RF/Telecom Power: Often expressed in logarithmic units (dBm or dBW) for convenience due to wide dynamic ranges.

Higher signal power usually means greater range and better reliability, but also higher risk of interference and regulatory issues.

Decibel (dB): The Universal Ratio

A decibel (dB) is a logarithmic unit expressing the ratio between two values, usually power or voltage. The dB scale is essential in electronics and communications because it compresses large ranges into manageable numbers.

• Power ratio: dB = 10 × log₁₀(P₁ / P₂)
• Voltage ratio: dB = 20 × log₁₀(V₁ / V₂) (assuming equal resistance)

Common dB units:

A 3 dB change ≈ double or half the power. A 10 dB change = 10× or 1/10th the power.

Signal Level

Signal level describes the measurable strength of a signal at a point in a system, typically in dBm (power), dBmV (voltage), or dBμV (voltage). Maintaining correct signal levels is vital:

• Too low: Weak reception, data loss, or dropped connections.
• Too high: Distortion, overload, or equipment damage.

Signal level measurements are crucial for system installation, maintenance, and troubleshooting.

Power and Amplitude Relationship

For sinusoidal signals:

• RMS amplitude: Aᵣₘₛ = Aₚₑₐₖ / √2
• Power (resistive load): P = Vᵣₘₛ² / R

Knowing amplitude allows calculation of power, which is critical for link budgets and transmitter/receiver design.

Decibel Calculations in Practice

Power ratio:

dB = 10 × log₁₀(P / P₀)

Voltage ratio:

dB = 20 × log₁₀(V / V₀)

Example:
A cable TV signal at 10 mV RMS:

dBmV = 20 × log₁₀(10 / 1) = 20 dBmV

A Wi-Fi signal at -70 dBm is weak but usable.

System gains and losses (amplifiers, cables, antennas) are added/subtracted in dB, simplifying complex link calculations.

The Decibel Scale

The decibel scale uses logarithms to represent ratios efficiently. It is used for both relative (input/output) and absolute (vs. a fixed reference) measurements.

• Relative dB: Compares two arbitrary values.
• Absolute dB: dBm (1 mW), dBW (1 W), dBmV (1 mV).

Example:
Transmitter output = 100 mW (20 dBm), receiver input = 1 mW (0 dBm):

Loss = 10 × log₁₀(1 / 100) = -20 dB

The decibel scale is essential for system design, compliance, and performance monitoring.

Signal Strength in Wired Systems

In cable TV and broadband, signal strength is measured in dBmV (decibels relative to 1 millivolt RMS into 75Ω). Systems use amplifiers and equalizers to maintain correct levels (+10 to +15 dBmV at the outlet is typical).

Losses: Cable attenuation, connectors, and splitters can degrade signal strength. Proper measurement and adjustment prevent dropouts, interference, or poor quality.

Signal Strength in Wireless Systems

Wireless systems (Wi-Fi, cellular, satellite, aviation) typically measure signal strength in dBm. Receiver sensitivity ranges from -120 dBm (very weak) to 0 dBm (strong).

Influences: Transmitter power, antenna gain, free-space loss, obstacles, and interference. Field strength meters and spectrum analyzers map signal coverage and identify weak spots.

Maintaining adequate signal strength is key for coverage, reliability, and regulatory compliance.

Antenna Gain (dBi, dBd)

Antenna gain measures how well an antenna directs energy compared to a reference:

• dBi: Gain over isotropic radiator (theoretical point source).
• dBd: Gain over half-wave dipole (practical reference).

Higher gain = more focused energy, greater range, but narrower coverage beam.

Effective Isotropic Radiated Power (EIRP)

EIRP is the total power radiated, factoring in transmitter output, antenna gain, and system losses:

EIRP (dBm) = Transmitter Power (dBm) + Antenna Gain (dBi) - System Losses (dB)

EIRP is crucial for regulatory compliance and determining coverage.

Factors Affecting Signal Strength

Signal strength is influenced by:

• Distance: Follows the inverse-square law (6 dB loss per doubling).
• Obstacles: Buildings, trees, and terrain absorb or scatter energy.
• Atmospheric Conditions: Rain, fog, or ionospheric activity can weaken signals.
• Interference: Other signals or electromagnetic sources.
• Cable Losses: Attenuation increases with length and frequency.
• Antenna Characteristics: Gain, orientation, and design.

Proper design, measurement, and adjustment are needed to maintain optimal signal strength.

Measurement Tools

• Spectrum Analyzers: Display frequency and amplitude of signals.
• Field Strength Meters: Measure signal power in the environment.
• Signal Level Meters: Used for cable/broadband systems.
• Software-defined Radios: For flexible, real-time signal analysis.

Regulatory Standards and Compliance

International organizations (e.g., ICAO, ITU, FCC, ETSI) set minimum and maximum signal strength requirements for different applications, ensuring:

• Safety (aviation, navigation)
• Interference control (broadcast, wireless)
• Quality of service (broadband, cellular)

Compliance requires regular measurement, documentation, and adjustment.

Troubleshooting and Optimization

• Identify weak spots: Use field strength mapping.
• Check cable/connectors: Replace or repair as needed.
• Adjust antennas: Optimize orientation and placement.
• Install amplifiers or repeaters: Boost weak signals.
• Shield against interference: Use filters and proper grounding.

Summary

Signal strength is a core metric in all electronic communication systems, directly impacting quality, reliability, and compliance. It is measured using specialized equipment and expressed in dB units relative to a reference. Maintaining optimal signal strength requires understanding power, amplitude, decibel calculations, antenna gain, and environmental influences.

By regularly measuring and optimizing signal strength, organizations can ensure robust, high-quality communication for users, meet regulatory requirements, and minimize downtime or interference.

Further Reading

• IEC 60027-3 Letter symbols to be used in electrical technology
• ITU Radio Regulations
• ICAO Doc 8071 - Testing of Radio Navigation Aids
• FCC Signal Strength Rules

If you need expert support with signal strength measurement, optimization, or troubleshooting, contact us or schedule a demo today!