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
