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.