Spectrum Analyzers in Telecommunications Training

Egyptian African Telecom Regulatory Training Center

• The center provides training on spectrum analyzers
• The presenter is Eng. Ayman Hamdy
• The presentation covers spectrum analyzers and their use in telecommunications

Contents

• Spectrum Analyzer Types
• Theory of Operation
• Spectrum Analyzer Settings
• Spectrum Analyzer Measurements
• Spectrum Analyzer Parameters
• Receivers vs. Spectrum Analyzers

Time-Domain vs Frequency-Domain

• Time-domain measurements show signals over time
• Frequency-domain measurements show signal strength over range of frequencies
• Oscilloscopes are used for time domain measurements
• Spectrum analyzers are used for frequency domain measurements

Spectrum Analyzer

• Measures input signal magnitude versus frequency
• Displays Amplitude vs. Frequency of RF/Microwave signals

Spectrum Analyzer Types

• Sweep Analyzer: Operates on super-heterodyne principle using a voltage-controlled oscillator and a mixer with an intermediate frequency filter
• Fast Fourier Transform (FFT) Analyzer: Uses digital signal processing to convert time-domain waveforms to the frequency domain

Theory of Operation (Block Diagram)

• RF input attenuator to control input signal strength
• Mixer for translating frequencies
• Intermediate frequency (IF) gain to amplify signal
• IF filter to select desired frequency range
• Logarithmic amplifier or similar circuit
• Envelope detector to measure signal amplitude
• Video filter to smooth output signal for display
• Local oscillator and reference oscillator to select target frequency

Spectrum Analyzer Settings

• Reference Level
• Resolution Bandwidth (RBW)
• Video Bandwidth(VBW)
• Sweep Time
• Span
• Attenuation
• Dynamic Range
• Displayed Average Noise Level (DANL)
• Detector Types
• Trace

Spectrum Analyzer Measurements

• Frequency
• Bandwidth
• Emission Mask
• Save on Event

Channel Power

• Measures total power over specified bandwidth

Spectrum Analyzer Parameters

• Frequency Parameters:
  • Frequency Range: Range of measurable frequencies (e.g., 9 kHz to 50 GHz)
  • Resolution Bandwidth (RBW): Ability to separate closely spaced signals
  • Video Bandwidth (VBW): Bandwidth of low-pass filter, used to smooth noise in displayed signal
  • Sweep Time: Time taken to sweep across selected frequency range
• Amplitude Parameters:
  • Reference Level: Highest signal power measured
  • Dynamic Range: Ratio of highest/lowest detectable signal levels
  • Noise Floor: Lowest measurable signal power
  • Attenuation: Amount of input signal reduction to prevent signal overload
  • Sensitivity: Minimum signal power distinguishable above noise
• Signal Processing Parameters:
  • Span: Frequency range displayed
  • Sweep Mode: Method of scanning the frequency range (e.g., continuous, single, zero-span)
  • Detector Types: Method for amplitude measurement at each frequency
  • Trace Averaging: Technique to reduce display noise
• Input/Output Parameters:
  • Input Impedance: Typically 50 ohms or 75 ohms
  • Input Power Range: Range of power levels the analyzer can handle
  • Pre-Amplifier: Improves sensitivity by amplifying weak signals
• Measurement/Display Parameters:
  • Marker Functions:Precise frequency and amplitude measurements at specific locations.
  • Trace Storage: Stores traces for comparison purposes
  • Display Resolution: Clarity and details of the measured spectrum.

Receivers VS Spectrum Analyzers

• Test Receivers: Measure commonly known signals with high accuracy, used in EMI tests
• Spectrum Analyzers: Used for general-purpose frequency analysis covering wide ranges, used in production, quality assurance, and certification
• Radiomonitoring Receivers: Optimized for tasks focused on spectrum monitoring

Test Receivers

• Measure signals accurately
• Used in EMI testing to meet standards
• Measure characteristics of known radio signals and bandwidth

Characteristics of a Test Receiver

• Characteristics of high measurement accuracy, specifically optimized operation for tasks, attenuation at the input, and the absence of automatic gain control (AGC),
• Regular calibration intervals are essential.
• Results display is according to standard operational procedures.
• Special marker function limit lines

Characteristics of a Spectrum Analyzer

• No pre-selection, 1st mixer at input, high accuracy, optimized operating concept, no gain control, Regular calibration intervals, result display and evaluation according to standard operational procedures, and special marker function limit lines
• Less important characteristics include audio processing, demodulation, increased temperature range, FSCAN, MSCAN (essential radiomonitoring functions).

Radiomonitoring Receivers

• Optimized for spectrum monitoring
• Fast signal detection
• Search across wide frequency ranges
• Detection of infrequent signals
• Storage of detected signals, further activities triggered by detected signals.
• Signal integration/localization of signal sources
• Measurements comply with ITU recommendations.

Characteristics of a Radiomonitoring Receiver

• Integrated preselection, Fast AGC, built-in antenna selector, optimized operating concept for monitoring tasks, essential radio-monitoring functions, audio processing, AC/DC power supply, built-in test equipment, increased temperature range, and stringent EMC requirements.

Receivers VS Spectrum Analyzers (Comparison Table)

• Comparing characteristics of spectrum analyzers vs. receivers.
• Analyzing differences in purpose, frequency coverage, dynamic range, sensitivity, selectivity, resolution bandwidth, sweep speed, measurement accuracy, and applications.