Category Archives: Troubleshooting

Review: The ARRL RFI Book (3rd Edition)

In my never-ending quest to search out useful reference books on EMC, I recently ran into the 3rd edition of “The ARRL EMC Book” (ISBN 9780872590915). First published in 1999, the new 3rd edition was released in 2010. For those unfamiliar with the ARRL (Amateur Radio Relay League), this is the national organization representing amateur radio operators (“hams”) in the U.S. Most hams are members of the league, which also publishes a range of useful operating, design and general radio reference books. Because hams are allowed to operate their two-way radios at up to 1.5kW, on occasion, this may be the cause of local interference to poorly-designed or poorly-shielded consumer products. Thus, several years ago it was decided to publish a reference book on RFI (radio frequency interference). In this article, I’ll describe the most important content and why you might want to buy it. More…

The RF Explorer 3G Released Today

RF Explorer is a handheld digital spectrum analyzer covering 15 MHz to 2.7 GHz. It is based on a highly integrated frequency synthesizer and double balanced mixer which offers high performance, compact size, low consumption and low cost. I’ve been beta-testing the unit for some time now and can confirm it works well as an affordable general-purpose analyzer.

Being battery-operated (chargeable via USB), it makes a great EMC troubleshooting tool. Probably, the major disadvantage is the limited user interface, being just seven push buttons, but there is available freeware PC and Mac remote client software to run and display waveforms. The display is also limited in resolution, but for the price, it’s tough to complain too much!

To read a review of the older model, which is very similar, click here…

The new RF Explorer is available now through SeeedStudio for $269.

Review: The Smart Tweezers Get Smarter

For years, I’ve looked for an affordable LCR meter to measure unknown components–especially surface-mount. I ran into the Smart Tweezers (Model ST3) a couple years ago and wrote up a short review. Since then, Canadian company Advance Devices, has updated the design (Model ST5). This model is very similar, but there are a number of improvements worth mentioning.

The Smart Tweezers in use. When measuring components mounted to PC boards, you need to realize the measurement includes all components connected to the two measurement nodes. In some cases, the component must be measured “out of circuit”. However, by adjusting the new source voltage control lower, it will avoid turning on most semiconductor junctions, enabling more accurate measurements “in-circuit”. (Photo courtesy Advance Devices.)

Most LCR meters make basic measurements, but with limited ranges or inadequate accuracy. The ST5 is calibrated to NIST standards and includes a Certificate of Calibration. In addition, most conventional LCR meters aren’t really optimized to measure today’s SM (surface-mount) components. It’s tough enough working with SM parts…let alone trying to identify them once a few parts on your workbench get mixed together. Read more…

All about current probes

Earlier this year, I published a tutorial on current probes and their application in Interference Technology (3/20/2012). The discussion included how to make your own probes from common ferrite cores, as well as commercial probes and how the DIY probes compared to the commercial ones. I finally wrapped up with how to use current probes to assess common-mode currents in I/O cables and how to predict pass/fail for radiated emissions by knowing the CM current on the cable.

Simple current probes made from clamp-on ferrite chokes.

EMC Troubleshooting Kit – The Complete Series

EDITOR’S NOTE: (Dec. 14, 2017) Test & Measurement World was merged into http://www.edn.com some years later. I’ve updated the links for you.
T&M World has asked me to increase the frequency of postings from 1/week to 2/week. Apparently, the postings are receiving lots of “clicks” from the readership, so they want more. Unfortunately, I couldn’t quite keep up with the blog here, so once the series was completed earlier this week, I thought I’d get back over here and provide the links to the complete troubleshooting kit postings.
I just completed the last installment of the blog series on the EMC troubleshooting kit I’ve been using for several years. I’m hoping it will be of interest and that it might inspire you to start assembling your own kit. While a bit expensive if you purchase one of the better spectrum analyzers, I found it’s paid for itself several times over through the years.
This last installment discusses some low-cost spectrum analyzer options and includes a complete listing of all the tools, components and troubleshooting gizmos. I haven’t really addressed most of the immunity testing (besides ESD), because that generally requires pretty sophisticated gear.
In case you missed some of these, here are the different postings:

Troubleshooting Kit – Part 1a (Emissions)

Troubleshooting Kit – Part 1b (Emissions)

Troubleshooting Kit – Part 2 (ESD Immunity)

Troubleshooting Kit – Part 3 (Detecting ESD)

Troubleshooting Kit – Part 4 (Radiated Immunity)

Troubleshooting Kit – Part 5 (Summary & Parts List)

Or, If you’d prefer, here’s a link to the whole series: http://www.tmworld.com/blog/The_EMC_Blog/index.php
We’ve been receiving a lot of positive comment and I’d love to hear other suggestions of tools and accessories you’ve used – especially for simple-to-use and low-cost immunity testing, but I’d appreciate your posting your thoughts on the blog entires themselves.

EMC Troubleshooting Kit – Part 2 (ESD Immunity)

This is a continuation of a description of my EMC troubleshooting kit as posted in the Test & Measurement “EMC Blog”. In the next few installments there, I’ll describe a few of the tools I use to test immunity of a prototype product to various stimuli. Bear in mind, immunity testing is a lot tougher to perform on the bench, so not all tests will be accommodated. To really ensure immunity levels, the product under test will have to be taken to a test lab.

So, what tests can be performed easily at the bench? These would include ESD, radiated immunity and certain pulse phenomenon. Of all the immunity tests, my experience has been that ESD and radiated immunity tests are the most likely to fail. In this installment, we’ll discuss one method to assess your circuitry or product against ESD phenomenon. There are several more ideas in The EMC Blog.

While you can’t beat an actual ESD simulator for pre-compliance testing, there are a number of simple ESD generators that will work well to at least give you a general feel for whether your circuitry is immune.

Here is a sample from the Test & Measurement “EMC Blog”:

One simple DIY ESD generator includes this BBQ grill igniter. You can purchase a replacement kit for a few dollars and the included wiring makes a good loop antenna. Holding this near your circuit board or close to the I/O and input ports to your product can indicate quickly if there are ESD issues. I’ve measured several volts into a simple UHF dipole antenna connected to an oscilloscope input. Edge speeds can be in the 50 to 200 ps range.

A simple piezoelectric BBQ starter is the heart of this ESD generator and can create large fields with 50 to 200 ps edges. The included wire makes a good loop antenna.

EMC Troubleshooting Kit

My EMC troubleshooting kit is packed into a Pelican 1510 roller case. Contents include a spectrum analyzer and various probes.

I’m currently describing the contents of my EMC troubleshooting kit in the Test & Measurement World EMC Blog. The first two postings (Part 1a and 1b) include detailed descriptions of the tools and accessaries I use for radiated emissions. The future postings will include a description of some tools used to assess radiated immunity and ESD. The kit is useful for limited pre-compliance testing, but it’s most useful for assessing radiated emissions. The kit also includes the usual range of resistors, capacitors, inductors, ferrites, copper and insulated tape and antennas.

Please feel free to add your own tools for troubleshooting in the comments below, or on the T&M World blog. Cheers, Ken

Troubleshooting Radiated Emissions at your Bench – Part 1

What do you do after returning to your workbench with a product that has just failed radiated emissions? In this multi-part series, I’ll describe simple and low-cost ways I use to help my own clients solve these issues. Most of the time, it’s possible to set up a simple 1 to 3 meter “measurement range” and determine whether a potential fix is required, or not.

PHILOSOPHY

First, a little troubleshooting philosophy. In many cases, you’ll run into more than one emission source causing the same harmonic frequency. The result is that you might apply a fix and the harmonic will do three things – either get reduced, have no change or better yet…get larger! It won’t be until you apply fixes to ALL the sources that you’ll yield positive results. This is what makes chasing down emission problems such a joy(!), I mean “challenge”!

There is also the issue of “balloon effect”; that is, you’ll beat down one frequency, only to have one, or more, pop up higher! It’s like squeezing a balloon in the middle – both ends get bigger! Often times, this is the result of resonances within your cabling or on the PC board.

In this installment, I’ll describe some simple reference antennas I use (you’ll be surprised) as well as setting up an area on your workbench where you can troubleshoot and apply potential fixes and really see whether you’re making progress, or not.

ANTENNAS 

The antenna you select should ideally be somewhere near resonance for the frequencies of concern, however, it’s not really that critical for troubleshooting purposes. So long as the antenna is fixed in length and fixed in place on the bench, you’ll receive consistent results. During troubleshooting, it’s more important to know whether the fix is “better” or “worse” or “no change” and as long as the test setup doesn’t change, the results should be believable.

Low-cost EMC antennas I use for troubleshooting, based on television "rabbit ears" and a UHF folded dipole.

Now, EMC antennas are not inexpensive, as you might imagine, so for general troubleshooting, I tend to use a couple television antennas – a pair of “rabbit ears” and a UHF “bowtie” (with TV balun to match 50-ohm coax). If the workbench is wooden, I’ll extend the antenna to approximate resonance (if possible) and tape it down to the bench with duct tape. If the bench is metallic, I’ll find a non-conductive support and position it some distance away from (or above) the bench. I usually use a test distance of about a meter, but as long as you can see the product’s harmonics on a spectrum analyzer, you’ll be able to determine your progress. Sometimes I need to insert a low-noise wide-band preamp between antenna and analyzer.

Now, obviously, ambient signals from broadcast radio, television mobile phones and two-way radio services will tend to interfere with observing the product harmonics. You may need to bring the antenna closer or set up the troubleshooting measurement in a basement or building interior away from outside windows. I usually record the known harmonics of concern and try to characterize them in relation to other nearby ambients.

CURRENT PROBES

If I know that one, or more, cables are the dominant radiation source, I might use a current probe to monitor the common-mode currents flowing on the cable, rather than an antenna. This also helps reduce the ambient signals, because current probes are generally shielded against e-fields and tend to be poor antennas. I’ll attach the probe to the cable with dominant emissions, moving it back and forth along the cable to achieve a maximum, and then fix it in place.

Commercial current probes can measure rf currents flowing on I/O cables - a very typical issue for radiated emissions issues.

BENCH

Next, I’ll clear off the workbench and (assuming the product is small) find a convenient place for it where I can work on it without moving it around much. I also place reference marks on the bench with tape, so I can reposition it for repeatable measurements. At that point, I’m ready to begin the troubleshooting and fixes while watching the emission levels.

Now don’t make the mistake of assuming that a 10 dB reduction on the bench with a one-meter test distance translates to the same reduction when measured at the test facility at a ten-meter test distance! During troubleshooting, we’re likely working in the “near field” where test distance is determined by terms of 1/r squared and 1/r cubed. At ten meters, we’re likely in the “far field” (plane waves) and the distance factor is closer to 1/r. Where “r” is the test distance. You can be fairly confident, though, that a reduction on the bench will equate to some reduction at the site.

More in the next posting!