The HP/Agilent 5381A is a direct-counting frequency counter that measures signals from 10 Hz to 80 MHz with a 7-digit LED display. Designed for production line testing, equipment calibration, frequency monitoring, and educational use, this instrument delivers repeatable results across industrial and laboratory environments.
## Technical Specifications
**Frequency Range:** 10 Hz to 80 MHz
**Display:** 7-digit LED readout
**Sensitivity:**
• 25 mV RMS (sinewave) from 30 Hz to 20 MHz
• 50 mV RMS (sinewave) from 10 Hz to 80 MHz
**Input Characteristics:** 1 MΩ impedance with 5 MHz
• ×10 attenuator: 200 V (dc + peak ac) DC to 40 Hz; 250 V rms 40 Hz to 1 MHz; 2.5 × 10⁷ V Hz 1 MHz to 50 MHz; 5 V rms 50 MHz to 80 MHz
## Key Features
• Direct counting architecture ensures straightforward operation and stable performance
• Manual gate time selection supports both fast production measurements and high-resolution calibration work
• External time base input via rear-panel connector enables connection of precision oscillators and permits ratio measurements
• High input impedance minimizes loading effects on measured circuits
## Typical Applications
Production line frequency validation, radio and test equipment service and calibration, continuous frequency monitoring, and technical education.
## Compatibility & Integration
Introduced in the early 1970s and manufactured through the early 1980s. Agilent Technologies discontinued support for this product. Aluminum case construction.
