HP / Agilent 5385A 10 Hz to 1 GHz Frequency Counter

The HP/Agilent 5385A is a dual-channel frequency counter delivering precise measurements from 10 Hz to 1 GHz. Channel A covers 10 Hz to 100 MHz; Channel B extends to 1000 MHz. With 9-digit resolution per second and a stable 10 MHz TCXO timebase, the instrument measures frequency, period, ratio, and time interval with single-shot resolution down to 100 ns and averaging resolution to 10 ps. The 12-character alphanumeric LCD and half-rack form factor support benchtop operation and ATE system integration across telecommunications, aerospace, and R&D environments.

## Technical Specifications

**Frequency Measurement**
• Channel A: 10 Hz to 100 MHz
• Channel B: 90 MHz to 1000 MHz (50 Ω fused input) or 50 MHz to 225 MHz
• Resolution: 9 digits per second
• Measurement Functions: Frequency, Period, Ratio, Time Interval (single-shot 100 ns to 100,000 s; averaging to 10 ps resolution), Period A, Ratio A/B, A By B, Totalize

**Sensitivity & Input**
• Channel A: 15 mVrms (50 Hz–100 MHz), 25 mVrms (10–50 Hz), 45 mV pk-pk (5 ns minimum pulse)
• Channel B: 10 mVrms (100–1000 MHz), 15 mVrms (90–100 MHz)
• Channel A Impedance: 1 MΩ ±, <25 pF (X1); 500 kΩ ±, <25 pF (X20)
• Channel B Impedance: 50 Ω ±
• Dynamic Range A: 45 mV to 4 V pk-pk; B: 10 mV to 7 Vrms

**Timebase**
• TCXO: 10 MHz
• Aging: <1×10⁻⁷/month
• Temperature Stability: <2×10⁻⁶ (0–40°C)
• Line Voltage Stability: <5×10⁻⁸ (±10%)
• Drift: <0.002 ppm over 14 days
• Accuracy: ±Resolution ±Time Base Error × Period

**Signal Conditioning**
• Attenuator A: X1 or X20 (X40 below 50 Hz)
• Attenuator B: Manual X1 to X18 (0–25 dB) or Auto AGC mode
• Low Pass Filter: 100 kHz nominal 3 dB point (Channel A)
• Coupling: AC
• Dual Slope Technique eliminates ±1 count error

## Key Features

• 12-character alphanumeric LCD display
• Automatic and manual trigger control with adjustable trigger level
• Half-rack width for flexible deployment
• AC coupling on both channels

## Typical Applications

• Telecommunications frequency validation
• Aerospace component testing
• R&D signal characterization
• Automated test system integration