The Keysight (Agilent) 11947A is a passive, solid-state transient limiter with integrated high-pass filter designed to protect sensitive measurement equipment from high-voltage transients and unwanted low-frequency signals. Built around a 50-ohm transmission line, this accessory combines a diode limiter, 10 dB attenuator, and high-pass filter to safeguard spectrum analyzers and similar instruments against accidental overloads and transient events during conducted emissions and precompliance EMC testing.
Technical Specifications
Frequency Range & Filtering
• Operating frequency: 9 kHz to 200 MHz
• High-pass filter cutoff: Approximately 9 kHz
• Impedance: 50 ohms
Insertion Loss
• Below 2 kHz: >30 dB
• 9 kHz to 50 MHz: 10 dB ± 0.5 dB
• 50 MHz to 200 MHz: 10 dB +2.2 dB −0.5 dB
• Calibration accuracy: ±0.2 dB at 25°C
Power Handling & Limiting Threshold
• Limiting threshold: 50 mW (+17 dBm)
• Maximum continuous input: 2.5 W average (+34 dBm)
• Maximum pulse input: 10 kW for 10 µs
• Maximum DC voltage: ±12 V
Reflection Performance
• Input SWR (9 kHz to 50 MHz): <0.13 (1.3 SWR)
• Input SWR (50 MHz to 200 MHz): <0.26 (1.7 SWR)
• Output SWR (9 kHz to 50 MHz): <0.09 (1.2 SWR)
• Output SWR (50 MHz to 200 MHz): <0.29 (1.8 SWR)
– Key Features
• Passive design with no external power requirements
• Diode limiting action reflects input power above threshold
• Fixed 10 dB attenuation below limiting threshold
• SWR specifications apply only below limiting threshold; reflection characteristics become unpredictable when limiting occurs
• BNC (female) input, Type N (male) output
• Physical length: 138 mm (5.4 inches)
– Typical Applications
• Conducted emissions measurements in precompliance EMC testing
• Protection of spectrum analyzers from LISN-generated transients during EMI testing
• Signal conditioning in test setups requiring low-frequency attenuation and transient protection
– Compatibility & Integration
Designed for use with Keysight (Agilent) spectrum analyzers and compatible measurement instruments requiring 50-ohm impedance matching and transient protection during EMC testing workflows.
