FieldFox Handheld Education Series Part 4: Techniques for Precise Time Domain Measurements in the Field FieldFox Handheld Education Series • Interference Testing • Cable and Antenna Measurements • Calibration and Alignment • Time Domain Measurements • Precise Power Measurements www.agilent.com/find/FieldFoxWebcasts Tom Hoppin Business Development Engineer Co-sponsored by © 2012 Agilent Technologies January 23, 2013 Techniques for Precise Time Domain Measurements in the Field Outline • Frequency and Time Domain Testing • Instruments with Time Domain Capability • Frequency to Time Transformation • Time Gating • Masking Effects • Distance to Fault Calculations • Optimizing Time Domain Measurements Frequency Domain Response Measured VSWR of complete system SPEC Frequency Which component is causing the problem ? Where is the fault located ? Time Domain Response Coaxial Line Coaxial Line Termination Input Connector Adapter Observe individual discontinuities as a function of time or distance Time or Distance Equipment Types with Time Domain Capability Time Domain Reflectometer (TDR) Vector Network Analyzer (VNA) Cable and Antenna Test (CAT) Analyzer N9918A FieldFox 30 kHz to 26.5 GHz 86100D DCA with 54754A TDR Module • True time-sampled measurements • Swept frequency measurements • Step Generator with fast rise time • Transform to time domain • Oscilloscope-based • High dynamic range receiver • Measure band-limited devices Measured Frequency to Time Transformation FieldFox VNA or CAT Measured Frequency Response Device under test (DUT) Measure S-parameter (e.g. S11 shown here) Activate Time Transform on VNA Calculated Time Domain Response Perform Time Transform on any S-parameter S21 S11 S12 DUT S22 Time Domain Example Amplitude Coaxial Transmission Adapter Line Metal Plate Horn Antenna distance t=0 Time 1 Time Domain Display 3 2 1 2 3 Time • Identify discontinuities • Large reflections are typically the problem • Time delay is round trip Measured Frequency Response Begin with the frequency response of S11 No Plate #2 #1 S11 Plate at position #1 Plate at position #2 Reflections from environment create additional ripple in frequency response Time Domain Transform – No Plate Transform into the time domain Coaxial Adapter Horn Antenna Environment • Locate discontinuities as a function of time • Time resolution is proportional to pulse width Time Domain with Environment Reflections #2 #1 Metal Plate Introduce the plate No Change distance Plate at position #2 Plate at position #1 Horn Antenna Time Gating Original TD Response 2 Filter responses in the time domain 3 1 Time Time Filter Time Bandpass Notch Time 2 Filtered Eliminate peaks outside filter Time 1 Time Examine frequency response of time filtered signal 3 Time Gating in the Time Domain Filter unwanted reflections Adapter Horn Antenna Environment Metal Plate Time Gate (bandpass) Gating in the Frequency Domain Return to frequency domain with gate active Original (no gate) Time Gate Applied Remove undesired reflections from the frequency measurement Masking in Coaxial Lines FieldFox VNA or CAT Lossy Coaxial Cable Open Cable insertion loss reduces the amplitude of the measured signal Enter average cable loss factor (db/m) or Select cable loss file (CAT mode) Time Domain with Filter FieldFox VNA or CAT Bandpass Filter Coax Coax Frequency Domain: S11 Load or Open Time Domain: S11 Input Filter Open Terminated with 50-ohm load Terminated with open Masking Effects with Filter FieldFox VNA or CAT Bandpass Filter Coax Coax Open Gate this reflection Time Domain Gating Frequency Domain with Gating Time Gate • Reflection from open includes masking effects of BPF • Cable loss entry will not compensate for filter masking Relating Time Measurements to Distance What is the physical Distance to Fault (DTF) ? Distance ? S11 measurement Damaged Cable Marker value = round trip travel time, tRT t DTF (m) RT vcable 2 where vcable VFc VF Enter Velocity Factor (VF) on VNA,CAT 1 r ( 1) c speed of light r relative dielectric constant of material Estimating the Velocity Factor (VF) FieldFox VNA or CAT 3 meters VF = ? Open Configuring the Frequency Range and Points Frequency Domain Sampled Data Df = Freq. Span (Points-1) Freq. Span Time– Frequency Relationships Pulse Width ~ 1/(Freq. Span) Max. Time Span ~ 1/(2Df) Not to scale Points = 101 10,001 Frequency Span and Pulse Width Pulse Width ~ 1/(Freq. Span) Coaxial Line Coaxial Line Termination Connector Adapter Time Domain using 500 MHz Span Time Domain using 4 GHz Span Adapter Connector 500 MHz Span Termination 4 GHz Span Frequency Span and Time Span Max. Time Span ~ 1/(2Df) = (Points-1) 2(Freq. Span) What is the max. cable length that can be measured? Copyright J M Briscoe and licensed for reuse under the Creative Commons License. VF=0.66 10,001 points Span (GHz) Max Time (ms) Range (m) 2.5 2 395 5.0 1 198 Configuring the Time Stimulus Lowpass Mode Bandpass Mode • Coaxial Cables • Coaxial Adapters • Waveguide Components • Couplers • Filters • Antennas Extrapolate to DC Mirrors the data S-parameter Data Bandpass Mode uses this data Lowpass Mode uses this data Other Applications Using Time Domain • Filter tuning • Transmission line impedance • Mixer group delay • SAW filter leakage • Calibration verification using airlines and shorts • Optimize time domain measurements using Window function • Optimize gating using Window function Conclusions • Introduced the relationship between the frequency and time domains • Discussed time domain as a verification and troubleshooting tool • Discussed time gating for isolating discontinuities • Investigated masking effects in the time domain • Introduced instrument configurations for proper DTF testing • Listed other interesting applications FieldFox VNA and CAT Analyzer Characteristics • Carry precision with you - Agilent-quality measurements • Full amplitude accuracy of ±0.6 dB at turn-on, -10oC to +55oC • Weather resistant, MIL-PRF-28800F Class 2 design • 6.6 pounds (3 kg) • Built-in GPS • 3.5 hour battery life N9912A 4/6GHz RF Analyzer N9923A 4/6GHz RF Vector Network Analyzer (VNA) N9925A 9GHz Microwave VNA N9926A 14GHz Microwave VNA N9927A 18GHz Microwave VNA N9928A 26.5GHz Microwave VNA N9913/4/5/6/7/8A RF and Microwave Combination Analyzers For More Information Web: www.agilent.com/find/FieldFox Literature: - Techniques for Precise Interference Measurements in the Field, application note, literature number 5991-0418EN - Techniques for Precise Cable and Antenna Measurements in the Field, application note, literature number 5991-0419EN - FieldFox Handheld Analyzers, brochure, literature number 5990-9779EN 4th in a series of monthly application webcasts • Sept 26, 2012: Interference Testing • Oct 24, 2012: Cable and Antenna Measurements • Nov 28 2012: Calibration and Alignment • Jan 23 2013: Time Domain Measurements • Mar 27 2013: Precise Power Measurements Check Back Co-sponsored by Registration: www.agilent.com/find/FieldFoxWebcasts Thank you for your time Questions? © 2012 Agilent Technologies References • Agilent Application Note 1287-12, Time Domain Analysis Using a Network Analyzer, Literature Number 5989-5723EN, May 2012 • Agilent Application Note 1304-2, Time Domain Reflectometry Theory, Literature Number 5966-4855E, May 2006 • Agilent Application Note 1287-8, Simplified Filter Tuning Using Time Domain, Literature Number 5968-5328E, July 2000 • Agilent Application Note 1287-10, Network Analysis Solutions Advanced Filter Tuning Using Time Domain Transforms, Literature Number 59802785EN, March 2001 • Agilent Application Note, Techniques for Precise Cable and Antenna Measurements in the Field, Literature Number 5991-0419E, August 2012.