Agilent/Keysight 3785A

The Agilent/Keysight 3785A is a specialized jitter generation and measurement instrument designed for testing digital transmission terminal and link equipment in CEPT and Bell hierarchies up to DS-3 (34368 kb/s). It performs production testing, field installation, and maintenance across cable, radio, satellite, and fiber optic transmission media. The instrument delivers six distinct jitter measurement types - absolute amplitude in Unit Intervals (UI) peak-to-peak, positive/negative jitter peak, jitter hit count, jitter hit seconds, and hit-free seconds - against CCITT Recommendation 0.171 tolerance masks.

Microprocessor control and HP-IB interface enable automated measurement sequencing and bus-controlled operation.

Technical Specifications

• Maximum bit rate handling: Four internal bit rates (up to DS-3, 34368 kb/s)


• Jitter measurement: Absolute amplitude in Unit Intervals (UI) peak-to-peak; positive or negative peak values; hit count with user-defined thresholds; hit seconds and hit-free seconds tracking


• Jitter generation: Sinusoidal phase modulation with manually controlled or swept amplitude and frequency per CCITT Recommendation 0.171


• Measurement filters: Two high-pass and one low-pass filter per bit rate, all CCITT-compliant


• Input capabilities: Clock or data inputs with optional internal filtering


• Jitter source: Internal crystal clock or external data stream modulation

Key Features

• Transient-free sweeping of CCITT-defined jitter tolerance masks


• Real-time jitter analysis against amplitude thresholds


• Four-rate portable configuration in single unit


• Front-panel frequency display for internal modulation


• Ergonomic front-panel layout with integrated switch and connector arrangement

Typical Applications

• CEPT and Bell PCM/TDM transmission system validation


• Production testing of digital transmission terminals


• Field installation verification and maintenance diagnostics


• Multi-media link testing: cable, radio, satellite, and fiber optic systems

Compatibility & Integration

• HP-IB interface for automated control and data sequencing


• Microprocessor-based operation for programmable measurement workflows