2015 Interference 101. Robin Jackman Application Engineer

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1 2015 Interference 101 Robin Jackman Application Engineer

2 Agenda What is Interference Introduction Definitions Spectrum Analyzer Concepts Concepts, Controls, Displays Making good measurements Measuring & Locating Interference Basic Direction Finding Techniques Logging Data Review On-Line Resources 2

3 What Is Interference There are a number of problems that indicate interference Adequate signal, poor reception Adequate signal, no access? No Signal? Interference = Degraded System Performance

4 Is It Really Interference? Understand system level issues Situational awareness what is happening around us 4

5 Suspecting Interference? Impaired signal at mobile? Impaired signal at base station? Where Is The Victim Receiver? 5

6 RSSI Rx Channel Understanding Interference Receiver pre-selector rejects out-of-band RF at input Narrow Bandwidth desired to reject out of channel signals Low Loss desired to allow sensitivity Rx Band Frequency/Channel 6

7 RSSI Interference Rx Channel Receiver De-Sensitization Signals passed by the pre-selector cause a reduction in the gain of the receiver amplifier. Rx is less sensitive, loss of coverage area Rx Band Frequency/Channel 7

8 RSSI Interference Rx Channel Receiver Blocking Strong signals passed by the pre-selector cause the receiver amplifier to go into compression. System is un-usable ie: Co-Channel or Adjacent Channels Rx Band Frequency/Channel 8

9 Fundamental Interference Fundamental interference is when two transmissions are at the same frequency Co-channel frequency assignments Some systems have fundamental interference since all sites use same frequencies. Tx coding reduces the effects Primary cause of cell capacity limitations. It is managed by careful power control 9

10 10 Fundamental Interference Generally speaking frequencies are always re-used, just not in local area. Hills combined with antenna aiming issues can allow coverage areas to overlap. Ionospheric variables = Long range interference

11 Intermodulation Interference Transmitter Involvement An external signal can back feed into a transmitter via the transmit antenna. Transmitters have diodes and transistors Antennas receive as well as transmit Other signals may enter a transmitter via the transmitter s antenna VERY common problem Transmitter 1 Transmitter 2 11

12 Intermodulation Interference Non-linear devices are found in: Diodes Transistors (amplifiers) Multi-couplers Cables Connectors Rust and corrosion Almost anywhere! PIM Tested? VHF PIM? Filters (Traps) often required 12

13 ~ Interference Intermodulation Interference - 3 Rd Order Intermodulation = 2F1 F2 - Most Common Rx Band Tx Band Pager F1 Harmonic 835 MHz 2F1 - F2 883 MHz F1 931 MHz F MHz 2 x F1 13

14 So Which Carriers Can Cause Problems? Mixing Product Calculator Enter F1 and F2 to operate F F F F F F2 2 F2 3 F2 4 F2 5 F

15 What Tools Do I Need? Protocol based tool will tell us our QOS is being impacted, it doesn t tell us WHAT is impacting the system Spectrum analyzers are the go to tool for looking at RF issues Spectrum analyzer categories Swept Low Probability of Intercept Real Time High Probability Of Intercept How long does a signal have to be on to guarantee intercept? 15

16 Agenda What is Interference Introduction Definitions Spectrum Analyzer Concepts Concepts, Controls, Displays Making good measurements Measuring & Locating Interference Basic Direction Finding Techniques Logging Data Review On-Line Resources 16

17 Amplitude Overview Spectrum Analyzer Display A 3 A 1 A 2 f 1 f 2 f 3 Frequency 17

18 Overview Traditional Spectrum Analyzer Block Diagram Frequency RBW # Trace Points Detector Type Span Ref Level Sweep Speed VBW 18

19 Overview Basic Spectrum Analyzer Controls Start Freq Stop Freq 19 Center Freq

20 Overview Basic Spectrum Analyzer Controls Reference Level 20

21 Overview Logarithmic Scaling To display very large and very small signals on the same screen, the spectrum analyzer uses a logarithmic scale based on the decibel. db = 10 log (P/ Pref) -40 dbm = mw -30 dbm = mw -20 dbm = 0.01 mw -10 dbm = 0.1 mw -3dBm = 0.5 mw 0 dbm = 1 mw 3 dbm = 2 mw 10 dbm = 10 mw 20 dbm = 100 mw 30 dbm = 1,000 mw 40 dbm = 10,000 mw When power doubles or halves, it changes by 3dB 21

22 Overview Basic Spectrum Analyzer Controls Resolution Bandwidth Control 22

23 Overview Resolution - RBW Filter level level level freq freq freq Wide Faster RBW Speed Narrow Slower

24 Overview Traditional Spectrum Display Detector RBW Limits # Trace Points POI = ms See Less 24

25 Overview Real Time Spectrum Analyzer Block Diagram Frequency RBW # Trace Points Detector Type Span Ref Level Acquisition Time VBW 25

26 Overview Real Time Spectrum Display Persistence 10,000 FFT/s POI = 100uS See More 26

Overview DPX Color Palettes & Color Scales

Occurrences to Color Raising The Minimum

27 Overview DPX Color Palettes & Color Scales Max. = 100%, Min. = 0% Max. < 100% Min. > 0% Color = How Often The Signal Is Present Adjust Mapping of Pixel Occurrences to Color Raising The Minimum Hides The Infrequent Lowering The Max. Emphasizes The Average 27

28 Overview DPX Versus Max Hold Conventional Spectrum Analyzer Display DPX Spectral Display Max. Hold Trace Infinite Persistence DPX Carrier Leakage Sweeping Trace 28

29 Overview Spectrogram The spectrogram shows how an RF signal changes over time It s basically a strip chart recorder for the spectrum information

30 Overview Swept Tuned vs. Real-Time Swept Analyzers Real-Time Analyzer Span = 40M RBW = 1 MHz 801 pts Span = 40 MHz RBW = 300kHz 801 pts 40ms 4629 Frames 2ms + 18ms = 20ms 18ms 2314 Frames 2ms Retrace + Process Time Frequency Frequency 112 MS/s 1 Frame = 8.64us

31 Overview Spectrogram Record your spectrum for long periods of time Playback problem periods

32 LAB Time! Lab Exercise #1 Monitor FM Broadcast Frequency Span Amplitude Reference Level Multiple Measurements

SignalVu-PC Benchtop Spectrum Analyzer features Optional

Wireless features like Wi-Fi, Bluetooth, P25 Mapping of

Real-Time Spectrum Analysis Real Time display showing WLAN

33 SignalVu-PC Benchtop Spectrum Analyzer features Optional Vector Signal Analysis (40 MHz Demod BW) Optional Commercial Wireless features like Wi-Fi, Bluetooth, P25 Mapping of multiple measurements for geolocation of signals Standard Real-Time Spectrum Analysis Real Time display showing WLAN signal Vector Signal Analysis of a QPSK signal FM signal analysis: DPX, Spectrogram, Freq. vs Time Wi-Fi Signal Analysis Mapping of signals to locate an interfering signal Signal Strength and Spectrogram

34 Agenda What is Interference Introduction Definitions Spectrum Analyzer Concepts Concepts, Controls, Displays Making good measurements Measuring & Locating Interference Basic Direction Finding Techniques Logging Data Review On-Line Resources 34

35 Measuring & Locating Interference Frequency Band Plan(s) Modulation Spectrum Shape System Level Issues Sound 35

Receiver Interference Spotting Hookup If interference is severe Disable traffic on that sector or channel Hookup an instrument receive antenna Make measurements This is the preferred measurement

36 Receiver Interference Spotting Hookup If interference is severe Disable traffic on that sector or channel Hookup an instrument receive antenna Make measurements This is the preferred measurement solution: it s faster If interference allows traffic to continue Hookup to redundant receive antenna Wait for traffic to slow down to make measurements Not the preferred measuring solution: it s slower 36 March 15

37 Rx Splitters Hookup Locations Location A Watch Out for DC Power! Location B and D Likely more sensitive than C Location C What the radio sees Easy to spot any BTS fault Less sensitive than B or D Diversity Antenna Rx 2 only Mast Mounted Preamp? Preselector & Power Insertion Rx Splitter 1 N Rx 1 A B Duplexer/Splitter Main Antenna Rx 1 Path Shown C Radio D Rx 2 To/From Switch 37 March 15

38 Logging Data: Spectrogram Log signal activity Remotely Long time periods When & how often is problem happening? 38

39 Logging Data: Action On Trigger User Defined Mask helps when staring in a span Mask Violation DPX Trace Combination DPX and Mask Test Actions on trigger: screen shot, record RF,

40 Logging Data: Basic Drive Testing 6 measurements can be measured and mapped automatically 40

41 Logging Data: Basic Drive Testing Log files can be mapped with simple, low cost software Mapping Received Signal Strength Indication aka channel power 41

42 Logging Data: Signal Parameters Frequency Occupied Bandwidth Crest Factor What Does It Sound Like? 42

43 Triangulation (Theory) To locate a signal need at least 2 good measurements We need to correlate signal strength Collect measurements from multiple locations Basic understanding of antenna patterns Keep Moving 43

44 Triangulation: Antenna Types Directional Antenna 44

45 Triangulation: Antenna Types Simple Dipole can be very effective Use NULL of antenna to locate weak or no signal Inverse Tone Use body as shield Add attenuation to reduce the effects of ambient signals 45

46 Triangulation: Target Zone Visible Source? Map and Compass Beware of reflections Beware F/B Ratio Beware of antenna pattern Beware of POI More LOB s the better! Area of Uncertainty 46 March 15

47 Triangulation: Antenna Types Once inside the target zone switch to monopole or nearfield antenna Use body as shield Add attenuation to reduce the effects of ambient signals 47

48 LAB Time! Lab Exercise #2 Monitor Wifi/Bluetooth DPX/DPX Ogram Masks Triggering eguide To Signals More Examples Download yourself

49 Agenda What is Interference Introduction Definitions Spectrum Analyzer Concepts Concepts, Controls, Displays Making good measurements Measuring & Locating Interference Basic Direction Finding Techniques Remote Monitoring Logging Data Review On-Line Resources 49

50 Interference 101 Understand your system Understand your spectrum Understand your interference Spectrum signature? How often is it occurring? Where is it coming from? What does it sound like? 50

51 Additional Resources Good Starting Location Interference Types Advice Lot s of Information

52 Additional Resources Search for licensed operators Spectrum frequency lists Lot s of information Technical Administrative Frequency List

Additional Resources Spectrum Management @

53 Additional Resources Spectrum Tektronix Videos eguide to Signals

54 Additional Resources Radio standards Info Transmission Theory Antenna theory transition.fcc.gov/cgb/consumerfacts/interference.pdf FCC Interference Industry Canada Interference 54

55 55

Understanding RF and Microwave Analysis Basics

Understanding RF and Microwave Analysis Basics Kimberly Cassacia Product Line Brand Manager Keysight Technologies Agenda µw Analysis Basics Page 2 RF Signal Analyzer Overview & Basic Settings Overview