Keysight (Agilent) 5245L Electronic Counter

The Keysight (Agilent) 5245L Electronic Counter is a modular frequency and time interval measurement instrument built on transistor-based circuitry with digital memory. Designed for precision metrology from the 1960s–1970s era, it delivers frequency measurements, period analysis, and frequency ratio calculations through an 8-digit Nixie display. The base unit spans 0–50 MHz; plug-in heterodyne converters extend measurement capability to 18 GHz, making it suitable for RF and microwave characterization across multiple decades of frequency.

Technical Specifications

• Frequency Measurement: 0 to 50 MHz (base unit)


• Period Measurement: 1 µsec to 10 seconds


• Period Averaging: 10 to 100,000 periods


• Frequency Ratio & Multiple Ratio: Direct measurement of two-frequency and multiplied ratios


• Decade Scaling: Up to 10⁹ scaling on any frequency input


• Internal Timebase: Oven-controlled 1 MHz crystal oscillator


• Display: 8-digit Nixie tube readout


• Input Impedance: 50 Ω (converter plug-ins)

Key Features Frequency Range Expansion via Plug-in Modules

• 5253B Heterodyne Converter: 50 MHz to 512 MHz; sensitivity −13 dBm to +13 dBm; 50 Ω input


• 5254C Heterodyne Converter: 150 MHz to 3 GHz; sensitivity −13 dBm to +13 dBm; 50 Ω input


• 5255A Heterodyne Converter: 3 to 12.4 GHz; sensitivity −7 dBm (50 MHz–15 GHz), −4 dBm (15 GHz–18 GHz); minimum pulse width 0.5 µs; minimum repetition rate 10 pulses/second; 50 Ω input


• 5255A with Auxiliary Input: 1–200 MHz auxiliary channel extends lower range to DC–200 MHz


• Combined with plug-ins: Measurement capability extends to 18 GHz


• Compatible plug-in units: 5253A, 5253B, 5255A, 5256A, 5258A, 5264A, 5265A, 5267A Metrological Accuracy Calibration is traceable to U.S. National Bureau of Standards. Accuracy maintained by plug-in unit specifications.

Compatibility & Integration The 5245L accepts all 52XX series plug-in modules. Adapter kits enable integration with later mainframes including the 5345A and 5360A. Early serial numbers (335 and below) may require modification kits to operate with certain plug-in units.