Stanford Research SR844 200 MHz Lock-In Amplifier

The Stanford Research SR844 200 MHz Lock-In Amplifier delivers high-performance signal detection across RF frequencies from 25 kHz to 200 MHz. Built on proven Digital Signal Processing architecture, this instrument combines exceptional sensitivity with dynamic reserve up to 80 dB, making it suitable for precision measurements in noise-rich environments.

– Technical Specifications

Signal Input
• Single-ended BNC connector with selectable input impedance: 50 Ω or 1 MΩ + 30 pF
• Bandwidth: 25 kHz to 200 MHz
• Damage threshold: ±5 V (DC + AC)
• Full-scale sensitivities: 100 nVrms to 1 Vrms, spanning –127 dBm to +13 dBm
• Gain accuracy: ±0.25 dB below 50 MHz; ±0.50 dB below 200 MHz
• Gain stability: 0.2 %/°C
• RF attenuation/gain: 60 dB attenuation or 20 dB gain in 20 dB steps
• Input noise floor: 2 nV/√Hz typical (50 Ω); 5 nV/√Hz typical (1 MΩ)
• Coherent pickup: <100 nV typical below 10 MHz; <2.5 µV below 50 MHz; <25 µV below 200 MHz

Reference Channel
• External reference: 25 kHz to 200 MHz with 50 Ω or 10 kΩ + 40 pF impedance; accepts 0.7 Vpp pulses or 0 dBm sine waves
• Internal reference: 25 kHz to 200 MHz with 3-digit frequency resolution and ±0.1 accuracy in the 3rd digit
• Harmonic detection at 2F from 50 kHz to 200 MHz
• Front panel reference output: 25 kHz to 200 MHz square wave, 1.0 Vpp nominal into 50 Ω
• Rear panel TTL output: 25 kHz to 1.5 MHz, 0 to +5 V nominal

Output Filters
• Time constants: 100 µs to 30 ks with selectable rolloff: 6, 12, 18, or 24 dB/octave

– Key Features

• Low zero-drift for stable dc-coupled measurements
• Precise RF phase shifting capability
• Digital output filtering with multiple time constant options
• Automatic reference acquisition below 10 s; sub-1 s within same frequency octave
• Dynamic reserve supports measurement of signals masked by noise up to 80 dB stronger

– Typical Applications

Optical heterodyne detection, phase-sensitive RF measurements, weak-signal spectroscopy, and precision impedance characterization in the 25 kHz to 200 MHz band.