Electromagnetic Interference (EMI) Assessments, Findings, & Solutions

Transcription

1 Electromagnetic Interference (EMI) Assessments, Findings, & Solutions 22 February 2017 HF Industry Association Spring 2017 Meeting 1

2 EMI Experience LWI EMI assessment locations over the past 5 to 7 years Various US Military Installations Rio Vista Wind Farm Budweiser Wind Farm Over 50 years of combined experience assessing and analyzing EMI in the HF range. 2

3 Sources of EMI Natural Not Mitigatable Galactic Atmospheric Man Made - Mitigatable Power distribution systems Switching systems Electronic devices Defective insulators HF EMI sources are time varying Magnitude and duration vary over extremely short periods of time. (milliseconds to seconds) 3

4 Approach Methodology Extended signal capture period Day Night Different days of the week (work week vs weekend) Full spectrum of interest capture Iterative Detailed analysis of large amounts of data Studied Characterized Documented 4

5 Man Made Wide Area Discoveries Human activity and interactions with modern electrical devices dramatically affect EMI Receive sites should not be located within Line of Sight (LoS) of public facilities and shopping areas Underground wires, pipes, rebar, or communications lines can affect EMI. Moisture dampens the affects Overhead Power lines act as antennas that radiate EMI produced by various sources. E.G. Bell insulators 5

6 Wind Farm Discoveries Wind Farms produce significant EMI in the HF range The source is the ac-dc power conversion equipment which may be located within the windmill or at a central conversion facility. EMI created by the conversion equipment can then be radiated by the tower and blades. The rotating blades provide a distinctive and periodic amplitude modulation 10 to 12 miles of range from a windmill is require to avoid significant interference. 6

7 Other Discoveries Erratic Interference from various discrete sources are prevalent though highly unpredictable Automobiles Plastic Extrusion machines Air conditioning units Wall Worts Fluorescent lights Uninterruptable Power Supplies Inherently produce a large amount of EMI Can be mitigated by Properly shielded coaxial cables Robust electrical grounding system Carefully engineered and maintained penetrations from the cabinets in which UPS are found Locating receive antennas as far from UPS as practicable 7

8 Techniques Signal Capture Antenna/Filter/Pre-amp Antenna Spectrum Analyzer 3-axis Time History Display Digital Camera Filters Preamp Spectrum Analyzer 3-Axis Display Computer Laptop Digital Camera 8

9 Current Techniques Signal Analysis Time lapse capture and identification of Signals of Interest (SOI) Characterization of SOIs currently a manual process involving snapshots of the spectrum Cross-comparison of Frequency (MHz) vs Strength (dbm) to Frequency (MHz) vs Time (Sec) Use of a digital camera is used to capture images for cross comparison Ray Vincent At work using the equipment and technique he developed over a period of greater than 50 years in signals intelligence 9

10 Future Techniques Current Technique Challenges Intensive manpower Hyper specialized skills in signal identification Leverages off old and near obsolete equipment New Technique Translate signal capture and analysis to Automatic Noise Analysis Tool (ANAT) Record signals Replay/analyze signals using a 3-axis time phased approach Use algorithms to search and identify SOIs for known interferers 10

11 Automatic Noise Analysis Tool ANAT automates existing techniques More accurate results Antenna Less Travel time for SMEs More time analyzing data than collecting data Plots data in real time in three dimensions showing Filters Preamp Spectrum Analyzer the time history Laptop ANAT and software application Eliminates dependencies on unsupported test equipment Replacement for the Develco 7200B 3-axis Time History Display Programmable to work with most modern spectrum analyzers Adaptability to function with older spectrum analyzers Provides the capability to record noise measurement site data for later analysis DVR like functionality Paving the way for automated analysis and cost reductions Enables waveform identification and anomaly detection using a noise signature library Provides the capability to remotely monitor measurement site data Provides the ability to annotate and automatically label plots for reporting 11

12 ANAT User Interface Rotatable in all 3 axis Frequency, Amplitude, and Time 12

13 ANAT User Interface Screen shots showing spectral distribution of six major reoccurring events from MHz to MHz Plots can be printed or tagged for later use can be used without the need for further work Image scaling, logging, plotting, viewing and rotating. As well as compressing, expanding and printing or tagging 13

14 ANAT - What can it be used for? To assess the suitability of a potential new receive site To study signal degradation at an existing receive site due to new sources of noise and/or interference To identify signal presence over any part of the spectrum over time To identify the source of a specific interfering signal or noise source To physically locate a specific interfering signal or noise source To perform automated spectrum occupancy analysis over time 14

15 Example: External Electromagnetic Environment of a receive building - Source analysis Emission from the UPS, 100 khz to 100 MHz Fine scale Structure of UPS Emissions, 2.5 MHz 15

16 Example: External Electromagnetic Environment of a receive building - Source analysis Internal cabinet to Main Ground Bus Current Current Probe at the Ground Stake 16

17 Example: External Electromagnetic Environment of a receive building 17 whip 3 from building Strength of interfering signals vs distance from building 17

18 Recommendations Site surveys are critical for HF receive performance Proper power distribution and shielding is critical for max performance Known wide area sources of man made EMI should be avoided: 18