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Interference Interference HuntingHunting

TechniquesTechniques

In Association with

RF Interference – What is it and Why all the Hype?

•As Wireless services grow, Interference (previously Uncommon) is on the rise•Interference naturally affects reception first where signal levels are normally small.•First Indicators include Noisy Links (Analog), Dropped Calls, Low Data-rate, High RX Noise Floor (Mobile Cellular), Poor Reception (Broadcasting)•All of the above problems equate to loss of revenue to the service provider who often pay a premium for their allocated spectrum.

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Types of Interference

•On-Band Interference (Antenna tilts and reflection)•In-Band Interference (Carriers from Other Services, Intermodulation Products, Harmonics of other Signals)•Impulse Noise (Lightening suppression devices, Motors, Ovens, Welding, Electric Fences, Power Lines, Light Dimmers, Diode Display Screens)•Harmonics•Passive Intermodulation (PIM)•Near-Far Problem•Intentional Interference

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Spotting Interference in the field

•Once the tell-tale signs are established from First indicators it is now time to bring out a spectrum analyser to take a look.•Once an interfering signal is characterized and detected using the tower antenna the next step is to use a ground level antenna to find the same signal. •This allows us the opportunity to search for the signal source by direction finding and signal strength.•For burst-type interferers the use of a max-hold or waterfall feature on a spectrum analyser which aids in determining the transmission pattern of a signal.

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Spectrum Max-Hold Display

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Spectrum Waterfall Display

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Spectrum Waterfall 3D View

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Locating the source

•After determining the frequency of interest we use our spectrum analyser with settings on the desired frequency we need to track using an Omni-directional antenna. Reason being that we determine the signal strength without direction. (Due consideration should be given using any gain factors)•We then use a directional antenna at the same input we used the Omni- directional antenna and note the bearing of the strongest signal strength using a signal strength meter.•Plotting this bearing on a map over multiple points (at least 3) will point to the source at interception points. (Care should be taken in built up areas where possibility of reflections can distort results).

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Locating the source

•Modern spectrum analysers have built-in mapping software electronic compasses and GPS receivers that can aid in time saving and plotting direction on maps easily.

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Fixing The Problems

•Once interference issues are identified. We propose resolution to the party breaching the spectrum.•In most cases the party in breach are unaware of their infringements and are willing to compromise especially if the methodology in determining the interference is properly documented. •Often lowering signal strength, filtering, cleaning/re-torque of connectors, removing environmental diodes, adjusting tilt and removing illegal TRX’s can immediately resolve issues.•Reporting the issue to authorities for resolution or legal action is often the final recourse.

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Conclusion

•With the push for modern society to go wireless, it brings with it more challenges as we struggle to maximise the spectrum at our disposal.•The advancements in digital technology and filter design allows us to maximise on the spectrum usage.•To determine and locate failure fast and accurately in modern systems is crucial for harmonious usage of our spectrum resource.•It is therefore most important to adopt the latest technology at hand to maximise on benefit in tracking down interferers.

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Thank You

Q&A

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