HP / Agilent 5345A 500 MHz Universal Counter

The HP/Agilent 5345A is a universal counter and timer delivering direct frequency measurements to 500 MHz, with extended range to 40 GHz via plug-in converters. Built on reciprocal measurement architecture, it achieves precise low-frequency characterization through period inversion. The instrument executes over 9000 measurements per second across the HP-IB interface and provides 2 ns single-shot time resolution, improvable to 2 ps with averaging. Dual input channels accept 50 Ω or 1 MΩ impedance selections with continuously variable gate times from 100 ns to 1000 seconds. Applications span metrology, calibration, and research environments requiring frequency, period, time interval, ratio, and totalization measurements.

Technical Specifications Frequency Measurement

Direct range: DC to 500 MHz

Extended range: Up to 40 GHz with HP 5355A converter (to 1.5 GHz) or HP 5356C converter head (to 40 GHz)

Reciprocal method for accurate low-frequency measurements via period inversion

Resolution: Up to 9 digits per second Time Interval Measurement

Single-shot resolution: 2 ns

Averaged resolution: 2 ps

Gate time: 100 ns to 1000 seconds continuously variable, or one signal period minimum

Measurement speed: Over 9000 measurements per second via HP-IB Input Characteristics

Dual channels (A and B)

Impedance: 50 Ω nominal or 1 MΩ (shunted <45 pF)

Sensitivity at X1 gain - 50 Ω: 25 mV rms sine, 75 mV peak-to-peak pulse; 1 MΩ: 25 mV rms to 300 MHz (50 mV rms to 500 MHz), 75 mV to 150 mV p-p pulse

Maximum input 50 Ω: ±7 V DC, 7 V rms below 5 MHz, 3.5 V rms above 5 MHz

Trigger level: Adjustable ±2.0 V DC

AM tolerance: Any modulation index above counter sensitivity

FM tolerance: 50 MHz peak-to-peak chirp in Auto Mode Common Input

AC coupled 50 Ω: 4 MHz to 400 MHz

AC coupled 1 MΩ: 300 Hz to 400 MHz

DC coupled: 0 to 400 MHz

Key Features

Reciprocal measurement architecture for superior low-frequency accuracy

Selectable input impedance matching diverse signal sources

Continuously tunable gate time accommodates both fast transient and long-term stability measurements

Modular expansion via industry-standard plug-ins extends frequency capability

Typical Applications

Precision frequency and period characterization in R&D and production

Time interval and jitter measurement for signal timing validation

Ratio and totalization measurements in calibration workflows

Metrology support for standards laboratories

Compatibility & Integration

HP-IB interface for automated measurement sequences and data logging

Compatible with HP 5355A and HP 5356C frequency converter modules