Agilent/Keysight 8981B

The Agilent/Keysight 8981B is a vector modulation analyzer engineered for precise analysis of digitally modulated microwave and IF signals. It characterizes in-phase (I) and quadrature (Q) signal components across modulation formats including QPSK, 16QAM, 64QAM, and 256QAM, making it essential for troubleshooting I/Q modulators, demodulators, and modulated signals in digital mobile radio, microwave radio, and digital video transmission systems.

The instrument connects directly to receiver demodulator I/Q outputs or IF test points, enabling comprehensive signal analysis throughout receiver chains. Real-time constellation, eye diagram, and vector diagram displays reveal signal quality degradations before link performance becomes unacceptable.

– Technical Specifications

• IF input and demodulator frequency range: 50 MHz to 200 MHz
• I vs. Q baseband bandwidth: 350 MHz (DC-coupled with internal filters)
• DC vector accuracy (I, Q): ±1% of full scale
• Quadrature imbalance: <0.5°
• Amplitude imbalance: <0.1 dB
• I-Q crosstalk: −60 dB or 1% of full scale peak (whichever is greater), DC to 350 MHz
• I versus Q timing accuracy: ±1.25 ns or <±2.5% of full scale IF input
• Delay accuracy: ±3% plus delay reference accuracy
• Time base jitter: 2% of full scale RMS for delays <200 divisions
• Differential voltage accuracy (I vs. Q): ±1% typical at 100 mV full scale deflection
• Input termination: 50 Ω or 75 Ω selectable
• Input coupling: AC, DC, or ground per channel
• Digitizing resolution: 12-bit for HPIB measurements
• Power requirements: 100/120/220/240 VAC (±10%), 48–66 Hz; 330 VA maximum
• Weight: Approximately 20 kg (45 lb) net

– Key Features

• Statistical measurements including closure, lock angle error, and quadrature error
• Marker-based phase, amplitude, and time measurements
• Magnitude and phase display at time marker or versus time sweep
• HPIB (GPIB) interface for automated measurements

– Typical Applications

• I/Q modulator and demodulator characterization
• Digital signal quality monitoring in mobile and microwave systems
• IF signal analysis and transmission link degradation detection
• Pre-BER transmission quality assessment

– Compatibility & Integration

The 8981B integrates with HP 8780A/8782B vector signal generators for coordinated signal generation and analysis workflows.