HP / Agilent 53181A RF Frequency Counter, 10 digits/s

The HP/Agilent 53181A is a high-performance RF frequency counter delivering 10-digit resolution at measurement speeds up to 200 measurements per second. Built for precision RF testing, it measures frequency from DC to 225 MHz on the primary channel, with optional second-channel capability extending to 1.5 GHz, 3 GHz, 5 GHz, or 12.4 GHz. The instrument combines fast acquisition with low sensitivity—20 mVrms from DC to 100 MHz, scaling to 40 mVrms at 200–225 MHz—making it ideal for weak-signal detection in demanding RF environments.

## Technical Specifications

**Measurement Capabilities**
• Frequency and period with 10 digits per second resolution
• Time interval measurement with 500 ps resolution
• Pulse width, rise/fall time, duty cycle, and totalize functions
• Phase angle and peak voltage measurements
• Ratio measurement when second channel is installed

**Primary Channel (Channel 1)**
• Frequency range: DC to 225 MHz
• Sensitivity: 20 mVrms (DC to 100 MHz); 30 mVrms (100–200 MHz); 40 mVrms (200–225 MHz)
• Input impedance: 50 Ω or 1 MΩ, AC or DC coupled
• Peak input voltage: ±5 Vac + dc (DC to 100 MHz)

**Optional Second Channel (Channel 2)**
• Selectable bandwidth: 1.5 GHz, 3 GHz, 5 GHz, or 12.4 GHz
• Sensitivity: 30 mVrms across rated frequency range

**Time Base Stability**
• Standard: <3 × 10⁻⁷/month (10 MHz)
• Option 010 (High-stability): <1.55 × 10⁻⁸/month
• Option 012 (Ultra-high stability oven): <3 × 10⁻⁹/month; <2 × 10⁻⁹/year

**Performance & Automation**
• Built-in statistics: average, min/max, standard deviation
• Automated limit testing with pass/fail indication
• Digit blanking for streamlined readout
• Operating temperature: 0°C to 55°C
• Measurement altitude: up to 3000 m

## Key Features

• Dual-channel configuration with independent frequency ranges
• GPIB (IEEE-488) and RS-232 standard interfaces; USB optional
• Compact form factor: 89 mm H × 213 mm W × 348 mm D; 7 lb
• Multiple input options including rear connectors for instrumentation racks

## Typical Applications

RF signal characterization, frequency stability monitoring, phase measurement, pulse analysis, and production test automation in RF design and manufacturing environments.

## Compatibility & Integration

Standard GPIB control supports integration into automated test systems. RS-232 talk-only mode provides legacy instrument communication. Optional USB interface enables modern data acquisition workflows. Configurable input coupling and impedance adapt to diverse signal sources and coupling requirements.