RFIMistakes, Myths & Misunderstandings

Tampa Bay Hamfest

By Mike Gruber, W1MG

December 12. 2015

Let’s Start With The Rules

• Important - Only the FCC is empowered to create and enforce rules regarding radio interference.– Federal law– Not state PUCs, local or state police, etc.

• Vast majority of cases involve a Part 15 device.– A small subset involve Part 18 a device

• CFLs, electronic ballasts, microwave ovens.

– Very small subset involve other device types.

Part 15 Devices

• Unlicensed devices• Three basic types you’ll likely encounter

– Incidental radiators• Often arcing or sparking source• No specified limits

– Unintentional radiators• Typically an electronic device• Has specified limits

– Intentional radiator• Rarely an interference problem

– Note: Fourth type called carrier current device.• Thanks to ARRL efforts, not an issue at the moment

Part 18 Devices

• Industrial Scientific & Medical (ISM) Devices– Consumer devices include electronic ballasts,

CFLs and microwave ovens

• Convert RF (at greater than 9 kHz) to some other form of energy.

• Prohibited from transmitting any form of intelligence or data.

The FCC’s Limits

• Absolute emissions limits specified for Part 15 unintentional radiators and Part 18 consumer devices.– Limits are high (Important)

• Interference can occur to nearby receivers• No protection guarantees• Devices can be legally marketed and sold

• And - no specified absolute emissions limits for incidental radiators!

The Bottom Line…• All licensed services (including Amateur radio) is

unconditionally protected from harmful interference caused by a Part 15 device– Part 18 has a similar provision except when an ISM band is

shared with the Amateur Service.• Rules are summarized by the ubiquitous Part 15 label:

– This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

Absolute Protection!So What’s The Problem?

• Devices often meet the limits, especially in Amateur bands.– Only way to tell is to test– Expensive and often not practical

• Limits are set pretty high.– Most cases argued on basis of harmful interference – not exceeding

specified limits.– Defined as a repeated disruption of intended radio communications.– Places burden to correct on device operator – not manufacturer.

• Typically a neighbor or you.• Often creates an awkward situation with neighbor / neighborhood.• FCC historically not sympathetic if you own the device.

• Key Point: Rules don’t help find the source.

Some Common Reported ProblemsA few Statistics…

• Most common problem is an unknown source.• Most common known source is power line noise

– Typically caused by arcing – rarely corona.– Classified as an incidental radiator under Part 15 rules

• No limits but must not cause harmful interference.

• Most remaining cases caused by consumer devices– Usually Part 15 / sometimes Part 18.

• Small percentage of remaining cases caused by intentional transmitters, cable systems, etc.

Some Typical Consumer Sources

• Typical devices include:– Switching mode power supplies & battery chargers– Lighting devices

• Part 15 LED devices• Part 18 fluorescent devices

– Variable speed dc motors• Washing machines, HVAC systems, furnaces, etc.

– TV Sets• Especially Plasma

– Computers, Peripherals & Associated Equipment• Monitors, routers, modems, etc. (Switching Mode Power Supply?)

– Electric and invisible dog fences– Electric blankets– Faulty Doorbell Transformers

Summary of “The Big Three”1) Part 15 Incidental Radiators.

– No specified limits.– Typically arcing sources, such as Power Line Noise.

2) Part 15 Unintentional Radiators.– Have specified limits.– Most consumer electronics.

• Almost Never…– Intentional Radiators.– Carrier Current Devices.

3) Part 18 (ISM) Devices.– Have specified limits (but lower than Part 15).– Primarily CFLs and electronic ballasts.

No Part 15 Immunity Limits

Who Ya Gonna Call?RFI Ghost Busters Not Found in Yellow Pages!

• RFI not your typical problem!– Every case can be different.– Solutions can vary widely depending on circumstances.– Skilled RFI investigators hard to find.

• I’ll just call:– The FCC

• Has enforcement power but lacks resources

– The ARRL• Can help with Cooperative Agreement.• Mostly a self-help resource.

– Power Company• Not responsible for locating consumer devices• May lack the resources to correctly locate power line noise.

– State PUC• No jurisdiction in matters involving radio interference.• May not know it.• May take interest if utility fails to respond to legitimate complaints.

• Anyone else has no jurisdiction.

Despite the Rules, Here’s The Reality

• If you want a timely resolution to an RFI problem, much of the burden ultimately falls on the you.– Locate the source or source residence in the case of

consumer devices.– If possible, power line noise sources.– Diplomacy a key ingredient toward success.

• Often no quick or easy solution without cooperation from device operator.– Requires patience!

Recommended Approach• Is it Power Line Noise or a Consumer Device?

– i.e., arcing or electronic source?• If power line noise:

– Distance may be greater– Report to utility– Use RDFing and signature matching.– Power Line Noise FAQ Page:– www.arrl.org/power-line-noise-faq

• If consumer device– Source typically a few hundred feet away or less.– Breaker Test.– “Sniff” approach helps locate residence, especially at HF.

The “Sniff” Method

• Key Point: Noise typically radiated by ac power wiring and cables, especially at HF.

• Consumer devices typically less than 250 feet away from antenna.

• Frequently in a home connected to the same power transformer secondary as the ham.

• Sniff out loudest transformer, then home.– Use minimum signal. – Use attenuation, reduce RF gain, or remove antenna.– Use highest possible frequency.

Ten Common Mistakes,

and how not to make them…

(1) What Is It?Often the First Mistake…

• Identifying source by sound often difficult if not impossible.– Many sources sound alike.

• Same source circuitry may be in multiple consumer devices.

– Too many sources to remember them all.• Number in the thousands.• Vary and change by the week.• Often just a guess.

• Even knowing the source doesn’t help find it.– Procedure still the same.

• Frequently the best practice is to ID source by finding it.– Consider the sound only as a clue.

(2) The Source Must Be IllegalBecause It’s So Loud

• Common misunderstanding – interference can still occur!• Most sources that we’ve looked at meet the FCC limits, especially

in the Ham bands.• Testing is often not an option.• Remember - The limits are high

– S9 plus noise from a nearby source is possible.

• We don’t have the ability to stop the manufacturing or marketing of otherwise legal devices – even if they are causing interference!

(3) Radiated vs. Conducted Emissions

• Surprise - No FCC radiated emissions limits below 30 MHz.– Most RFI at HF is not radiated by the source device!– Wavelength too long relative to device size.– House wiring and power lines act as antenna– Most HF RFI caused by conducted emissions

• More about this later.

• Most RFI above 30 MHz caused by radiated emissions.– Only FCC radiated emissions limits above 30 MHz.

(4) It’s EverywhereJoe Even Hears It Across Town!

• Some scenarios are statewide and multi-state.• Limits typically confine scope of problem to

about 250 feet or less.– Record for (illegal) consumer device is about 1,000

feet.

• Most power line noise sources typically ½ mile or less.– Record is about 8 miles, but…– Extraordinary case involving high voltage facility.

What’s Really Going On?

• Multiple local sources near each reporting station.– Common problem and many sources sound alike.

• Yes - some unsolved cases remain a mystery, but…– Substantial power required over wide bandwidths.– Antenna abnormally wideband.– No apparent intelligence being transmitted.– Seems difficult to intentionally radiate such a signal for

no apparent reason.

(5) It’s Coming From That Pole!

• Poles often misidentified for a variety of reasons.– Can be conducted from home attached to

transformer.– Pole “with more stuff” can be better antenna.– Standing waves…

Peaks & Nulls

(6) It’s The Cable System

• Common Mistake – Noise radiated by cable may not be from the cable system.

• Grounds are all bonded – both at service entrance panel and on pole.– Neutral bonded to ground at service entrance.– Required by code.

• Conducted emissions often common mode, thus may involve a ground path.

• Radiation can occur from outside of cable shield and other ground conductors.

• Don’t be fooled…

(7) It’s Not Me…I’ve Already Eliminated My House As The Source.

• Yet, a very high percentage of consumer devices are ultimately located in the complainant’s home.– Even after they claim to have eliminated it as a

source.

• Always trip the main breaker.– Listen with a battery portable.– If noise goes away, further isolate source by tripping

individual circuit breakers.– Unplug devices on circuit until noise goes away.

(8) Nothing In My House Could Cause Something Like That!

• Really? Think switching mode power supplies, battery chargers, wall warts, computers, lighting devices, etc.– Note: Many modern electronic devices have switching

mode power supplies. These are a common cause of RFI.• Please – don’t guess – trip the main breaker while

listening with a battery portable.

(9) I Simply Don’t Have The Equipment…

• Common Misunderstanding: It will take an expert with expensive equipment to find this one…– Spectrum analyzer typically not needed or useful.– Spectral plots can be misleading.

• Often a simple battery powered shortwave receiver is a powerful tool.– Breaker test.– Remove antenna if necessary to “sniff” for loudest source.

• Power meters, etc.

• Additional tools available on ARRL Web, including…– Antenna (Cost approx. $10.)– Attenuator

(10) It Must Be The XYZ CompanyThey were just here last week...

• Scenario: The XYZ Company just installed <fill in the blank> in my neighborhood. Now I hear S9 noise. It must be them! This is the doom of Amateur Radio as we know it…

• Reality: There are potentially hundreds if not thousands of RFI sources within range of a typical ham station in a residential neighborhood.

• Don’t guess or assume!

(Bonus - 11) Multiple Sources

• Scenario: Ham observes noise at 145.250 MHz.– Attributes noise to Cable Company.

• Incorrectly assumes numerous (all) other sources also caused by the Cable Company.– Even if sources drift or sound nothing like cable

leakage.

• Less of an issue with digital cable signals.

(Bonus - 12) It May Be Your Radio…

• IMD Products, Images, Overload, etc.– Beware: Can create phantom signals if nearby

transmitters are present.– The 160 and 2m bands often most susceptible.– Problem appears to be the transmitter(s), but it’s not.– Attenuator test is simple and easy!– The cure is a filter at the receiver – not a complaint

to the FCC.

(Bonus - 13) Power Line Noise Sources Rarely Visible

• Generating laundry list of visible “defects and issues” is a common mistake.

• Most power line noise sources not visible by eye.• Utility may fix many sources but not your

problem.– Utility will typically loose interest after spending time

and money.– RDFing and signature analysis is best approach.

Finally - Never Bang On Poles!

• Common practice by some, but…– Seriously – This can be dangerous.– You could be liable for damage.– May generate additional noises.– Doesn’t pinpoint source hardware

• There are better ways…– Ultrasonic dish– Hot-stick sniffer (Not for hams)

The Radar Engineers Model 250

The clear-plastic parabola is an "ear" connected to an ultrasonic detector that lets utility personnel listen to a power-line arc. Using its pistol-like gun sights, an RFI investigator can accurately pinpoint the offending hardware on a pole once the structure has been found. It is not a suitable instrument for locating the pole, however. It’s only as good as the RFI investigator’s ability to verify the structure containing the source.

Conclusion & Summary• Keep your expectations realistic.• Know the basics.• Roll up your sleeves – the problem often becomes yours by

default.• Don’t over complicate or assume anything. You can do it…

– Don’t skip steps.– Use good practice.– Guessing or speculating about the source often does not help!

• Never underestimate the importance of diplomacy.– Be a good neighbor!– Remember - A cooperative neighbor is often the only timely solution.

• ARRL Provides a pamphlet you can download.– www.arrl.org/information-for-the-neighbors-of-hams

• An ounce of prevention - Listen before you buy…

Additional Help…• See the Power-Line Noise FAQ Page for additional help: www.arrl.org/power-line-noise-faq• See Mike Martin’s RFI services web site for locating tips: www.rfiservices.com• See AC Power Interference Handbook, available from the ARRL. This book is dedicated the subject of finding and fixing power-line noise. Features in-depth coverage of noise signature techniques.

More Information ARRL Web Site RFI Pages

• Source of both technical and non-technical RFI information• Includes FCC information and information for your neighbor• ARRL RFI Home Page:• www.arrl.org/radio-frequency-interference-rfi• RFI@arrl.org

And, Of Course…

The End…QUESTIONS and ANSWERS

(Stump the Speaker!)