A Practical Guide to EMC

This appeared in the April 2014 issue of IEEE SEM Chapter newsletter, Wavelengths. They’re electrical engineers, so they must know what they’re doing, right?

  • Put everything in metal boxes. No, make that two lead boxes, in fact.
  • Don’t make anything electric, use steam. But not for the European market because of the Simple Pressure Vessel Directive.
  • Don’t make anything with wires which connect to anything else. Communication should be by semaphore, hydraulics, or string.
  • If you must use electricity, ground everything – even signal lines.
  • Use metal connectors, metal shells, metal switches, metal fasteners; solder them all together and ground everything.
  • Put ferrites on everything, even string.
  • Don’t use electric motors. Use mice in little cage wheels. Put ground straps on the mice.
  • Don’t have any ventilation holes. They allow RF energy in and out of the enclosure. I know it’s bad for the mice, but, we live in a disposable age.
  • Bond everything to a ground plane – portable devices have the potential to generate way too
    much interference anyway.
  • Don’t use any removable parts – they compromise the integrity of the enclosure. Mice should be sealed in at the time of manufacture. This stops pooh from getting everywhere too.

2014 Tech study guide: RF interference, common transmitter and receiver problems

There were some substantial changes to this section. More questions were added about how to troubleshoot RF interference problems and a couple of questions were eliminated, including one about alternator whine…Dan

Since Murphy’s Law—the law that states if anything can go wrong, it will—applies to amateur radio as much as it does to any other pursuit, at some point you will have to deal with problems. These may include overload, distortion, feedback, and interference.

Let’s first consider interference. All of these choices are correct when talking about causes of radio frequency interference (T7B03):

  • fundamental overload
  • harmonics
  • spurious emissions.

Any of these could cause interference to a TV set or radio, and you will want to take steps to find and eliminate that interference. If someone tells you that your station’s transmissions are interfering with their radio or TV reception, you should first make sure that your station is functioning properly and that it does not cause interference to your own radio or television when it is tuned to the same channel or frequency. (T7B06)

While it’s not very likely that your amateur radio station will interfere with a neighbor’s cable TV service, it can sometimes occur. The first step to resolve cable TV interference from your ham radio transmission is to be sure all TV coaxial connectors are installed properly. (T7B12)

Your amateur radio station may interfere with a nearby radio receiver if your signal is so strong that the receiver cannot reject the signal even though your signal is not on the frequency to which the receiver is tuned. When a receiver is unable to reject strong signals outside the AM or FM band, it can cause a broadcast AM or FM radio to receive an amateur radio transmission unintentionally. (T7B02) One way to reduce or eliminate the overloading of a non-amateur radio or TV receiver by an amateur signal is to block the amateur signal with a filter at the antenna input of the affected receiver. (T7B05)

Another device that often experiences interference from amateur radio stations is the telephone. The telephone wires act as antenna and the telephone itself demodulates the signal. One way to reduce or eliminate interference by an amateur transmitter to a nearby telephone is to install an RF filter at the telephone. (T7B04)

All of these choices are correct when considering what may be useful in correcting a radio frequency interference problem (T7B07):

  • Snap-on ferrite chokes
  • Low-pass and high-pass filters
  • Band-reject and band-pass filters

Interference works both ways. Your neighbors may have wireless devices, sometimes called “Part 15 devices,” that can interfere with your station. A Part 15 device is an unlicensed device that may emit low powered radio signals on frequencies used by a licensed service. (T7B09) All of these choices are correct when considering what you should do if something in a neighbor’s home is causing harmful interference to your amateur station (T7B08):

  • Work with your neighbor to identify the offending device
  • Politely inform your neighbor about the rules that require him to stop using the device if
    it causes interference
  • Check your station and make sure it meets the standards of good amateur practice

Perhaps the most common problem that amateur radio operators have is distorted or noisy audio when transmitting. There are many reasons for poor audio. All of these choices are correct if you receive a report that your audio signal through the repeater is distorted or unintelligible (T7B10):

  • Your transmitter may be slightly off frequency
  • Your batteries may be running low
  • You could be in a bad location

Reports of garbled, distorted, or unintelligible transmissions is a symptom of RF feedback in a transmitter or transceiver. (T7B11) Sometimes, garbled or distorted audio when operating FM is the result of over-deviation. Talk farther away from the microphone is one thing you can do if you are told your FM handheld or mobile transceiver is over-deviating. (T7B01)

Hams oppose tower project

A recent article, “Radio towers spark high wattage opposition,” in the online edition of All Point Bulletin, the community newspaper of Point Roberts, WA, caught my eye. At issue is the construction of five, 150-ft. AM radio towers. According to the article, “The antennas will produce a broadcasting signal for KPRI Ferndale 1550 AM which bills itself as ‘your number 1 South Asian voice.’ The company currently broadcasts at 50,000 watts during the day and 10,000 watts at night.”

Towards the bottom of the article, this paragraph appears:

Ham radio operator Steve Wolff told the crowd that Point Roberts’ ham radio club members were unanimous in their opposition to the towers. Citing an objection filed with the FCC, he recounted how one ham radio operator in Ferndale had received burns from the radio energy captured by his radio tower from the KRPI broadcasts.

First, I find it quite ironic that amateur radio operators would actually oppose a tower-construction project. Second, I’ve never heard of anyone getting RF burns from his tower from a broadcast signal. Seriously, how close would the amateur radio tower have to be to the broadcast tower to capture enough power to cause an RF burn?

From the trade magazines, impedance matching, EMI basics, open-source hardware

elelctronic-design-logoBack to Basics: Impedance Matching. electronic design editor (and amateur radio operator) Louis Frenzel is the author of this short e-book on impedance matching. Note: this e-book was intended for engineers and does use a fair amount of math, but nothing you can’t figure out if you work at it.

EMI Basics. This article  comes from the book Signal Integrity Issues and Printed Circuit Board Design by Douglas Brooks. I like the discussion of how twisted pair wire helps prevent radiation.

Interview With SparkFun’s Director Of Engineering. Peter Dokter is director of engineering for SparkFun, one of the major suppliers of open source hardware. SparkFun designs and sells things useful and interesting to the aspiring electronics tinkerer, including microcontroller boards, Bluetooth, GPS, Wi-Fi, LCD displays, e-textiles components, robots and robotic parts, motors, motor drivers, buttons and switches, tools, and books.

Amateur Radio in the News; CERT, RFI, “magic band”

San Ramon CERTCERT volutneers, amateur radio operators ‘leap’ into action
The San Ramon Valley Community Emergency Response Team (CERT) program along with local amateur radio operators participated in a mock communications drill on Saturday. Volunteers placed hundreds of stuffed “CERT green” frogs placed throughout the community to help simulate victims of a major disaster.

Florida resident cited for ham interference
In an unusual case, the FCC cited Ruben Lopez of Pomona Park, Fla. for harmful interference with amateur radio frequencies. He has 30 days to respond to the Enforcement Bureau or risk being fined up to $16,000 for each violation and having his equipment seized. In this case, the subject of the interference is a well pump, according to the agency.

Sweet sound of ham radio
Timaru (New Zealand) radio enthusiast George Boorer is thrilled with the national switchover to digital television. It means after 40 years he can head back out to his “radio shack” and tap into the six-metre international amateur band, otherwise known as “the magic band”.


ARLB008 FCC Seeks to Reassess RF Exposure Limits

fcc-sealI find the topic of RF exposure very interesting. It seems to me that back in the 1960s and 1970s, when I was just getting into radio, we never even thought about exposure. Now, people go crazy over it. Here in Ann Arbor, for example, the power company is installing “smart” power meters that send data via a cellular system back to a system that monitors power consumption. These devices are  low power at a low duty cycle, yet consumers are getting all bent out of shape about it…Dan

ARLB008 FCC Seeks to Reassess RF Exposure Limits

ARRL Bulletin 8 ARLB008
From ARRL Headquarters
Newington CT April 4, 2013
To all radio amateurs

ARLB008 FCC Seeks to Reassess RF Exposure Limits

On March 27, the FCC released a First Report and Order, Further Notice of Proposed Rulemaking and a Notice of Inquiry (ET Docket Nos. 13-84 and 03-137). The documents seek to reassess the FCC’s RF exposure limits and policies, as well as to propose changes to the FCC’s rules regarding human exposure to RF electromagnetic fields. These proposed changes would affect the Amateur Radio Service (Part 97) rules. The First Report and Order can be found on the web in PDF format.

In the 201-page document, the FCC noted that “[p]eriodic review of the government’s rules and regulations to ensure they have kept pace with current knowledge and changing needs is an important characteristic of good government, and we here will advance the process of providing a comprehensive review and modification, where appropriate, of this Commission’s various rules pertaining to the implementation of the National Environmental Policy Act (NEPA) requirements for environmental reviews, specifically those reviews related to health and safety of radiofrequency (RF) emissions from radio transmitters. Our actions herein are intended to ensure that our measures are compliant with our environmental responsibilities and requirements and that the public is appropriately protected from any potential adverse effects from RF exposure as provided by our rules, while avoiding any unnecessary burden in complying with these rules.”

The document is divided into three parts: a First Report and Order (First R&O) and a Further Notice of Proposed Rulemaking (FNPRM) in ET Docket No. 03-137, and a Notice of Inquiry (Inquiry) in a new docket, ET Docket No. 13-84. In the R&O, the FCC looks at several technical and semantic issues — initiated in 2003 — to be revised and updated; in the FNPRM, the FCC proposes to further update and revise its procedures and treat all services equally.

In the Inquiry, the FCC seeks comments to determine whether its RF exposure limits and policies need to be reassessed. “Since consideration of the limits themselves is explicitly outside of the scope of ET Docket 03-137, we propose with the Inquiry to open a new docket to consider those limits in light of more recent developments,” the FCC said. “The Inquiry is intended to open discussion on both the currency of our RF exposure limits and possible policy approaches regarding RF exposure. We look forward to developing a complete record to determine whether the current rules and policies should remain unchanged, or should be relaxed or tightened.”

According to the FCC, mitigation matters are “post-evaluation procedures to ensure exposure limits are not exceeded, such as labels, signs, barriers, enforcement and occupational issues.” In its Notice of Inquiry, the FCC included clarifications related to the application of occupational exposure limits for devices and at fixed transmitter sites. The FCC noted that it “should be helpful to licensees to codify our earlier adopted policy with regard the use of occupational/controlled limits at Amateur Radio stations.”

This policy was first established in the RF Report and Order of 1996, but it was not incorporated in the rules at that time. It allows amateur stations to be evaluated “with respect to occupational/controlled exposure limits, as long as appropriate training and information has been provided to the amateur licensee and members of his or her immediate household. Other nearby persons who are not members of the amateur licensee’s household must be evaluated with respect to the general population/uncontrolled exposure limits.” The FCC will codify this policy by adding a paragraph as a new sub-section in Section 1.1310 — radiofrequency radiation exposure limits — to its rules.

The FCC pointed out that one goal of the general exemptions from routine RF exposure evaluation proposed “is to avoid specific exemptions for particular services and ensure a consistent set of rules without exceptions.” With this in mind, the FCC is proposing to delete the special exemptions from evaluation in the Amateur Radio Service in Section 97.13(c) of its rules.

“We appreciate that Amateur Radio operators are knowledgeable about the appropriate use of their equipment, such that separation distances are likely to be maintained to ensure compliance with our exposure limits,” the FCC said. “However, since the existing amateur exemptions are based only on transmitter power and do not consider separation distance or antenna gain, exempt transmitting antennas that are unusually close to people could potentially lead to non-compliant exposure levels.” The FCC said that a separation distance of at least 24 feet would meet its proposed exemption criteria, “considering a currently exempt 50 W transmitter at VHF in accord with Section 97.13(c) and assuming an antenna gain of 6 dBd.”

The FCC noted that existing classification of amateur exposure as occupational “is consistent with use of our proposed general exemption criteria based on general population exposure limits because awareness of exposure greater than the general population limits is required in all occupational settings, including amateur households. Application of the general exemptions proposed here to Amateur Radio installations would preclude the possibility of overexposure and require further evaluation only when necessary, giving guidance for both fixed and mobile transmitting antennas.”

The FCC invited comments on how this would affect the amateur community: “Parties that support maintaining the current exemption based on power alone are requested to explain how it provides adequate assurance that the public is protected against exposure to RF energy in excess of our limits and the extent of the burden imposed by this proposal. We encourage interested parties to comment on the relative costs and benefits of the proposed changes in this section, as well as those of alternative approaches.”

“The ARRL has an RF Safety Committee, consisting of experts in the field,” explained ARRL Chief Executive Officer David Sumner, K1ZZ; “The committee members, as well as Board members and staff are reviewing the lengthy document and will formulate a response.”

Comments will be accepted until 90 days after the R&O, FNPRM and Notice of Inquiry are published in the Federal Register (this can take up to six weeks after its release by the FCC). Reply comments will be accepted until 150 days after publication in the Federal Register.

From my Twitter feed: WWV, smart meters, freeDV

History of WWV and the NIST Time Stations http://t.co/xKWgOX0mwj #shortwave #swl #dx

Concerned about RF effects from smart meter? Check out http://t.co/mht0hvGSrP for technical analysis of meter signals

Been playing with FreeDV? Looks like some very recent improvements have been made. http://t.co/4MtGko4U75 #hamr #DV

Found my 20m noise source

About three months ago, I finally put up another 20m antenna—an end-fed, half-wave antenna. Right off the bat, I was flummoxed (I love that word) by the high noise level. It was nearly S9, obliterating all but the strongest signals.

I thought it had to be something to do with the antenna. I was not experiencing any noise on any of the other bands, after all.

As it turns out, though, the source of the noise is the laptop power supply. I had taken the laptop somewhere on Wednesday, and when I returned it to the shack that evening, I switched the rig over to 20m before connecting the power supply back to the laptop. No noise! When I plugged the power supply into the laptop, the noise jumped up to S9 again.

What’s really confusing about all this is that I don’t hear this noise on any other band. They’re all completely quiet. Like I’ve said before, sometimes 40m is so quiet that I wonder if the antenna is even connected.

At any rate, the last couple of days, I’ve been working 20m with the power supply disconnected, running the laptop off the battery, and the results have been quite good. This evening, for example, I worked several DX stations, including 6W/HA0NAR in Senegal.

Minutes of the January 2013 ARRL Board Meeting

ARRLThe annual meeting of the ARRL Board of Directors was held January 18-19, 2013 in New Orleans, and the minutes of the meeting were recently published. You can download and read the entire minutes yourself, but here are a few items that I found particular interesting:

  • #16. Mr. Kramer presented the report of the Chief Operating Officer. Finding appropriate ways to support the growth and activities of ARRL-affiliated clubs was an issue highlighted during discussion of the report. As chairman of the Programs and Services Committee, Mr. Norris advised the Board that the committee has established a subcommittee to address the issue.
  • #21. Mr. Carlson, as chairman, presented the report of the EMC Committee and entertained questions. There was a discussion of how to stimulate electric utilities to resolve cases of power line interference to amateur stations.
  • #25. The board adopted seven legislative objectives for the 113th Congress. To read them all, download the minutes, but in addition to the usual items such as, keeping and defending our frequencies, #6 aims at ensuring that two-way radio communications be exempt from distracted driver laws, and #7 supports legislation authorizing the FCC to appoint an electrical engineer to their staffs to provide technical expertise.
  • #28. The ARRL has created “the ARRL Amateur Radio Service to Scouting Award, to be administered consistent with the Community Organization Award program of BSA.”
  • #32 The board will appoint an ad hoc committee to look into the recent Logbook of the World problems and provide some recommendations at the July 2013 meeting.
  • #37. Lucy Ann Lance, a local broadcaster here in Ann Arbor, MI was awarded the “Bill Leonard, W2SKE, Professional Media Award, developed to honor professional journalists whose outstanding work best reflects the enjoyment, importance and public service value of the Amateur Radio Service.”

As I was club president here in Ann Arbor for several years, and for several years served as the Michigan Section Affiliated Club Coordinator, I’m especially interested in #16. I’ve e-mailed my director and vice-director to get their takes on it, and I would encourage all of you to do likewise for any of the items that are of interest to you.

From my Twitter feed: Ontario Science Center demos ham radio

Ontario Science Centre Demonstrates Ham Radio Digitally Remastered http://t.co/sU2HgoYO

My catch-phrase! RT @K5KVN: New meme! @K5PO says: Put A Ferrite On It! http://t.co/CxrqFIMY

Amateur Radio Quiz: A Log of dBs: By H. Ward Silver, N0AXn0ax@arrl.netI f there is a single unit of measurement b…http://t.co/lkdKX9cb