EMI RFI Amateur Radio Presentation - VE6TN
Transcript of EMI RFI Amateur Radio Presentation - VE6TN
EMI RFI Solutions for the Modern Ham
Presentation To:Calgary Amateur Radio Association (CARA)April 22, 2002
Barry Middlebrook, P.Eng.Assistant Director, RAC
April 22, 2002 Barry Middlebrook, P.Eng. VE6TN 2
What is EMI/RFI?
Electromagnetic Interference Radio Frequency Interference Do we need to be concerned about
dealing with it? Who is responsible to resolve a
problem? Things we can do to minimize the
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A Bit Of History
1920’s – AM broadcast receivers where the hot topic. No immunity. Amateurs observed “quiet hours”.
1950’s – Television became the hot topic. No immunity. Amateurs established TVI committees to help.
What about in the 21st Century?
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Television. Satellite, cable, amplified antenna, VCR’s, PVR’s, DVD.
Surround Sound stereo systems. 5+1 speakers, multi-zone.
Computers. Powered Speakers. Telephones. Call display, digital
recording, multi-line. New. Home networking, wireless house.
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It IS BETTER Nowdays!
Rules for amateurs, rules for consumer devices.
FCC Part 15 ““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.”
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HUMOUROUS BUT TRUE !
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RAC Activities onYOUR Behalf RABC
The Radio Advisory Board of Canada provides broadly based, unbiased and technically expert advice to the Government of Canada and to the industry on all matters regarding the management and use of the radio frequency spectrum in Canada.
CARAB The Advisory Board is a non profit consultative group consisting of
members of the Radio Amateurs of Canada (RAC) and the Radio Regulatory Branch of Industry Canada (IC). Its function is to provide a consultative forum between Canadian radio amateurs and the regulator. Other than provided herein, CARAB is acknowledged as a consultative entity. It is understood that agreed upon action is not binding on either the RAC or IC.
ARRL and IARU Sit on Boards and participate representing
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The 2 Top Issues Affecting Amatuer Radio Restrictive Covenant Provisions
Municipal Rules for Towers Private agreements from Condo
and neighborhood associations. Interference Complaints
Dealing with Consumers Dealing with Manufacturers Dealing with Regulators
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EMCAB 1 and 2
EMCAB-1 “Electromagnetic Compatibility Advisory Bulletin - Immunity of Electrical/Electronic Equipment Intended to Operate in the Canadian Radio Environment (0.010 - 10 000 MHz)”
EMCAB-2 “Criteria for Resolution of Immunity Complaints Involving Fundamental Emissions of Radio communications Transmitters”
Safety Code 6 – Limits exposure. 1 KW into Yagi at 50 ft. is generally
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This explosion in radio communications has stressed the radio frequency spectrum and increased the risk of disruption in reception and the number of problems encountered when using electronic equipment
The requirement is that both the amateur and the affected party each be reasonable and cooperate to resolve the problem
EMCAB-2 Procedure to be followed Web Reference
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People Need to Work Together to Resolve Issues If there is an interference complaint
…. You have a problem. You cannot bury your head in the sand and ignore it.
IC and a radio inspector does have the authority to impose limits. It is rarely used, and if it is you do have an appeal recourse.
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The Government Powers The Radiocommunication Act provides enabling powers to
the Minister beyond those previously applicable under the Radio Act. Specifically, Section 5(1)(l) states, in part:
".... the Minister may, taking into account all matters that the Minister considers relevant for ensuring the orderly establishment or modification of radio stations and the orderly development and efficient operation of radiocommunication in Canada,... …make determinations as to the existence of harmful interference and issue orders to persons in possession or control of radio apparatus, interference-causing equipment or radio-sensitive equipment that the Minister determines to be responsible for the harmful interference to cease or modify the operation of the apparatus or equipment until such time as it can be operated without causing or being affected by harmful interference"....
These powers permit the Minister to make determinations regarding immunity-related interference complaints involving both Radio Apparatus and Radio-Sensitive Equipment (RSE) and to issue orders to resolve them.
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Tools and Suggestions
Immediately stop operating. Develop the communication and repertoire needed to provide an opportunity to be able to resolve it.
Dealing with people and respecting them is the first part of the solution.
Technical issues are secondary. Your personal diplomacy will be key to your ability to work with them to resolve the problem. Being allowed a future opportunity to fix the interference in a spirit-of-cooperation and living in peace with your neighbor is on the line.
Brochures, educational video, website.
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So What Can You DoTo Resolve Interference? MAKE SURE YOUR STATION IS
CLEAN CONFIRM THAT YOUR OWN
HOUSE IS RFI/EMI FREE DON’T BE CHEAP, GET THE
NEEDED DEVICES TO FIX THE PROBLEM
ASK FRIENDS FOR ADVICE AND HELP
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Things You Can Do In Your Station That May Help.
a) Have a proper matched antenna. Nothing beats a tuned circuit for proper transmitting and reducing RFI problems.
b) Use a transmit low pass filter. If your VSWR at the filter is less than 1.5:1 then the filter will work as intended, but if your VSWR is above that point then it probably doesn’t do anything and may even contribute to your RFI problem.
c) You can install a line isolator similar to the T4 from Radioworks (www.radioworks.com) which will reduce feedline radiation. A poor antenna match, line VSWR, or a ground loop within the shack can result in RF signal on the outside of your coax instead of on the inner conductor. A line isolator is basically a series of ferrite beads that choke any RF that is on the braid eliminating this type of interference. Note that the line isolator should be installed before the lowpass filter to improve its effectiveness. (Rig > Line Isolator > lowpass filter > antenna.
d) Make sure all of your connections are tight and properly sealed against moisture. e) Have all of your equipment grounded together to a common point such as the linear
amplifier. f) Ensure that your own house is RFI free. If you suffer interfere with your own TV or
stereo, then chances are your neighbor will also have a similar problem. Your own house will be the worse-case scenario since it is closest and tied into the same power and ground as your radio.
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Resolving the Problem
Cable/Satellite Television. Make sure all connections are “tight”. 7/16” wrench is your best friend.
Audio Rectification for stereos or computer speakers. Shorten leads and add Ferrite to any cables.
Telephone. Add ferrite to phone line and power cable.
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Ferrite is yourFriend ! Install ferrite on signal line AND on
power lead. 5 Turns minimum 10 turns preferred
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Most audio equipment uses unfiltered MOSFET power devices
MOSFETs are by their very nature a high-gain, high-power and high-frequency device. They have characteristics different from normal bipolar transistors, which allows them to run at the high power and drive speakers directly without filtering circuitry on their outputs. These power devices are biased in the audio frequency range for proper amplifier operation. High frequency RF radio signals are within the operating bandwidth of the device, and the gain at these higher frequencies is actually higher than at audio frequencies. Thus, what is a stable controlled gain stage to audio is in fact an unstable high-gain amplifier that is running in full saturation at RF frequencies. Hence the MOSFET is behaving like any good solid-state device operating in saturation, it has becomes non-linear and acts as a diode-detector and demodulates the radio signal down to speech.
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The old FilterCapacitor trick - Caution Need to be careful. They can bias
a MOSFET into high-current and cause the amplifier to fail.
Use 0.01 to 0.02 uF
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Resources Telephone filters
www.k-comfilters.com and www.coilcraft.com (model TRF-RJ11)
Ferrite Cores www.amidon.com with Material #43,
66, 73, or 77 Amidon FT-240-43 at $9/ea USD www.palomarengineers.com
Radio Shack sells Snap-on filter chokes (#273-104)
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Be nice. Resist an angry response Have proper tools to resolve the
problem. Decide ahead of time who will pay for the ferrite devices.
Exercise common sense practices. Should you really run the amp during the Superbowl?
Don’t go and “ask” for trouble